Engine: Turbo                                                                                                 FAQ Home

Volvo Maintenance FAQ for 7xx/9xx/90 Cars                                                                                                                     Version 5.0

Turbo Preventive Maintenance

Turbo Idle and Shutdown

Turbo Performance Problem Solved by Checking the Little Things

Turbo Replacement

Turbo Rebuilders

Turbo Blows Black Smoke; Poor Acceleration

Turbo Blows Smoke: Overfill Oil

Slow Throttle Response After Turbo Replaced; Diagnosis

How Does Wastegate Operate?

Turbo Wastegate Adjustment

CBV Valve Operation

Excess Crankcase Pressure in B230FT

Normal Oil Consumption for Turbo

Oil in the Intercooler

Gasoline Recommendations for Turbo Engines

Turbo Expiration

Turbo Oil Leaks

Turbo Oil Return Pipe Seal Replacement

Remote Oil Filter O-Rings

Lack of Turbo Boost

Turbo Overboost

Turbo Loses Performance at Boost

740T Has Weird Deceleration; Anti-Stall Valve Hose

Turbo Has Power Loss and Cherry Manifold: Knock Sensor

Poor Idle: Turbo Intake Gasket Leaks

Intake Manifold Gasket Leaks

Exhaust Manifold Gasket and Studs

Broken Turbo Exhaust Stud

Turbo Exhaust Stud Replacement

Turbo Hose Preventive Maintenance

Turbo Hose Sources

Turbo Hose Clamps

Turbo Preventive Maintenance. [Query:] I'll be ripping the turbo off the exhaust manifold soon. Is there any bench top inspection I can do on the turbo? Any turbo tips while the turbo is off the car? [Suggestions:]You can do a little pm work here. Take the oil return tube and make it spotless. Any blockage from oil gunk has to be removed. Some turbo shops recommend replacing it; their warranty is void if you don't! Do the same with the oil supply line. An automotive machine shop vat is a good way to make sure they're clean, or a good soak in carb cleaner. Check the rotating assembly by spinning it by hand; it should rotate freely. Look for any obvious signs of contact, or any damage by debris. You'll need to look as far up in the housing as you can. If you are really industrious, match mark the housings and remove them to expose the impellers. Word of warning here: stripped and broken bolts are common here. Also check for radial clearance in the bearings by moving the shaft perpendicular to its axis. There will be a fair amount of play, but it should not move more than maybe a sixteenth of an inch at the end of the shaft (this is a very rough estimate, use good judgment or get someone with experience on this to check it for you). Another area to examine is the waste gate section. Cracks radiating outward from the hole are common and considered to be normal. Only if they have really opened up, or if there are other cracks through the housing, should this piece be replaced. Depending on the mileage and your wallet thickness, consider a new water-cooled center section and ease your worries. For around $400 you can put your housings on a new cartridge; or they will do it for you (recommended). A shop I would recommend is Turbo Engineering Consultants in Colorado; friendly, easy to deal with. Phone number available if you're interested.

Also check out http://www.alliedsignal.com:80/turbos/sitemap/index.html for a sitemap and good general information and pictures related to turbo operation and maintenance.

[More on Turbo Wear Inspection.]  [Query] I currently have the Turbo off.  The Turbo has 100,000 miles and had no problems before taking it from the car.   What can I inspect (without tearing the Turbo apart) to see what the condition is of my Garrett Intercooled Turbo unit. Any information is appreciated.  [Response:  Thomas] Make sure the compressor wheel has a small amount of play (turbo's have full floating bearings) Check for excessive wear on the compressor blades(not likely), Carefully clean out any coke or sludge in the oil galley's, oil return pipe and oil feed pipe. Check the internal horn passages for cracks. I have a 130K on my turbo, I hope I can get more then that out of it. I wish I knew what exactly makes a turbo last the longest.  Any how just make sure its all intact.

Turbo Idle and Shutdown.   [Query:] The figure of a minute or two before shutdown was relevant for the older, non water cooled turbos. Yours ('86) should have water cooling, and thus only require a few seconds.  Is this so? [Response:]  Yes, it is.  The reason the two minute cool down period was required is that so called 'first generation' turbos had oil cooling, but no water cooling. The effect of oil cooling is less, and thus these units ran MUCH hotter than later, water cooled turbos - after a long drive they could be glowing red! This is hot. And it can burn the oil. This does not cause a problem while the car is running, because the oil pump keep recirculating the oil around, so it doesn't stay in the turbo long enough to burn (and it has that nice oil cooler next to the main radiator as well). The problem is that as soon as you shut down the engine, the oil pump stops. If the turbo is still spinning, it has no pressurized lubricating oil.  The oil that sits in the turbo stays there and can burn and coke. If solid sludge particles form in the turbo bearing (which is an oil bearing), they can score the bearing journals - kind of like your very own grinding machine inside the turbo.

Enter second generation turbo.These units have the same oil cooled bearings, but they also have water cooling - much like an engine has oil bearings and water cooling. The
effect on the turbo is two fold: One, it runs much cooler - doesn't glow red or anything (the exhaust manifold might (read: does...), though - but that's a different story). Aside from that, the water keeps recirculating even after the engine is switched off, due to convection (i.e. hot water rises).  Hence, the danger to second generation turbos is considerably reduced.

So, one would ask, what is the reason for the few seconds of idle after starting and before switching off? Simple. In the first few seconds after starting (even after the oil warning light is off!) the oil pressure is lower, and fresh oil may not have reached the turbo yet - and if you race the engine, the turbo will spin fast with insufficient oiling of the bearing - not good. Likewise before switching off:  when the engine stops the oil pumps stops immediately. The turbo, however, may keep on spinning for a few more seconds if the engine was racing just before being switched off - simply because of inertia. So again the turbo would spin fast with insufficient oiling.  This (and the 1st generation problems mentioned before) is the reason behind the different 'turbo pre- and post- oiler' systems.

This is also why a synthetic oil is best for a turbo car (bearing (sorry) in mind the drawbacks of synthetics) - apart from any other  qualities they may have, synthetic oils maintain their properties MUCH better in high temperatures - and while a normal engine normally  wouldn't have such high temperatures in it, the turbo does.

[Response:  David Farrington]  Basically your "Idling down" is merely sitting at idle for 30 seconds or a minute before shutting down the car. The turbocharger can literally get red hot during spirited driving. Naturally we don't normally do that, but depending what our drive has been like - 70 miles at 80 on the freeway is not the same as 5 miles at a steady 25 mph. This idle time gives the turbocharger time to cool down a bit, both with some water cooling and more importantly some oil cooling and circulation. One can purchase and install automatic oil timer pump kits that circulate the oil automatically, but good habits are far cheaper.
First word on owning a turbo engine - change the oil & filter! I'm religious, every 3k miles and the turbo seems fine at 190k miles although I'm starting to think of a pre-emptive turbo cartridge replacement.

Turbo Performance Problem Solved by Checking the Little Things. [Symptoms:] 740T experienced a number of problems:  occasionally hard to start, with intermittent rough idle and stalling out; frequent stumble under boost once motor was warm; lack of power.  On a cold start, it ran flawlessly, but I never run much boost on a cold motor, so I don't know if it would have stumbled under boost when cold.  Despite many FI and ignition components being checked or replaced, the problem continued. Everything had been checked out or replaced (fuel pumps, relays, ignition system, ECU, etc).
[Response 1:] The problem turned out to be caused by a VACUUM LEAK in a rubber tube under the intake manifold.  The tube only leaked when it was hot, and subject to vibration/movement of the motor.  My mechanic has been elevated to "saint of motors."  The bright side is we now have all new ignition, wires, ECU, fuel pumps, etc.   There is a moral here:  "Go ahead and get your hands dirty...really dirty."  Unless you know the car's history fully, remove every rubber hose and inspect it closely, even if they are hidden below the intake manifold and throttle body (yes Virginia, that may be a very oily area).  A minor vacuum leak there seems to have major consequences with the injection system.  The way-high boost TB guys have already found that the main boost hoses can give out and cause poor driveability.  I am here to tell you that even with stock boost getting to the local grocery store can be risky if the various minor vacuum hoses develop hidden cracks.
[Response 2:] I had a poor driveability problem with my 87 760t on take off. Turned out to be a vacuum leak on the big hose from the air box to the intercooler.....and a big dent in the pocketbook since the thing is a preform with a couple other hoses molded into it......$130 or so. I just replace all the vacuum hoses every 5 years or so.

Low Oil Pressure.  See Oil Pump: Wear and Replacement for more information.

Turbo Replacement.
Removing the Turbo Unit.  [Tip from Rob Bareiss]  Repalcement of newer turbos is not bad as the older ones. There are water lines to deal with now, but they don't get in the way much. You might get real lucky and have a Mitsubishi turbo, which will make you happy. They're pretty easy to replace due to the way the studs face. If not, even with the Garretts, its' not as bad as it was. I always recommend replacing all the exhaust nuts, and to try to save the studs I split the nuts with a chisel. This can save a great deal of aggravation (it's an old VW trick- the studs on VW heads always broke).  To identify if you've got a Mitsu or not, the Mitsu turbos have a big clamp in the center between the compressor housing and the exhaust-driven outlet housing. It's like a huge hose clamp made of stainless steel. If it's loosened up the two housings can rotate relative to each other (and it'll leak there). If you don't have this clamp it's not a Mitsubishi.  They started using it in 89, and a good many replacement turbos are Mitsubishis.  Any case, good luck, hope you don't break any studs, and if you do, get ready to pull the head. Don't try to fix exhaust studs in place.

[More tips]  I'm writing now to say that I have completed the turbo replacement on my '84 240. Replacement was purchased from IPD and included everything needed (plus some duplicate gaskets with the watercooling conversion kit). IPD sent instructions, plus I had the Bentley book, and things were relatively straightforward except some hassle getting bolts off and back on in tight places. (It seemed to me I needed to have two hands plus my head/eyes plus a light all in a space that was only big enough for any two of those at a time!) Another hassle was my error in putting the O2 sensor back in before the support bracket (mine's on the bottom); had to take the O2 sensor back out, then do this bracket, which also had spacers between it and the block. I finally figured out I could use masking tape to hold the spacers on the bolts in the bracket while I moved it up into position one-handed and got the bolts started. I've been driving it to work again this week, with no leaks, no smoke, and notably improved power. Should note also that doing it myself saved considerable money; counting new oil pipes (I reluctantly got both, but probably only really needed the "to" pipe) and the IPD costs, I had ~$900 in parts. Local dealer quoted a cost for the job at ~$2100, and one independent shop quoted ~$1400. You'll need the range of basic hand tools, PB Blaster or equivalent if there is one (I used it often, including on exhaust manifold and exhaust flange studs and did not break any of them), and I think a sturdy vice is a must as well to get the manifold and turbo separated, but it was overall not that difficult (at least now that I'm done with it!!) I did have to move the exhaust flange studs to the new turbo, but PB Blaster and the two-nut method worked OK. I at first put the propane torch to the old turbo intending to loosen the studs, but in retrospect it wasn't necessary, once I got the hang of the two-bolt method.
The parts and instructions left me with a pretty good feeling about IPD also (although they apparently just buy the turbo from a different company in Colorado and put it and a watercooling kit together in a bigger box).I don't mean this as an advertisement or a criticism; I'm glad I got the IPD kit and if an ordinary mortal like me can do this replacement, probably alot of others can too!

Installing a Rebuilt Turbo.  [Tips from Dave Schermbrucker]
Just installed my rebuilt turbo (745); thought I'd pass on a couple of hints.

1. Installation should take about 2 hours.  You will need to get under the car.

2. Try to install the oil drain line before dropping the turbo/manifold unit into place; it's real pain to connect the flange to the turbo core from below once the unit is in place.  I say this because most turbo rebuilders and Haynes says to crank the engine a bit after installing, prior to connecting the oil drain, to make sure oil is running through the unit.  Forget it.  Just hook it up.  If you're worried about oil feed, undo the top supply line adter installation to check that oil is getting through.

3.  Alternative to 2:  use small studs instead of bolts to connect the oil outlet; that way you're only struggling to mount some nuts on a couple of studs rather than trying to feed the bolts from below in an impossible location.  I had to remove the wastegate actuator to get the bolts in; tricky and time-consuming.

4. Use new banjo bolts if you possibly can, since they make it so much easier to snug up the new copper o-washers on the oil and water lines.

5.  If you have the oil filter sender assembly (most do) you'll need a 36mm socket.

6.  You should remove the lower stud from the turbo exhaust-to-downpipe fitting; otherwise it's impossible to line up the turbo unit.  After you locate the unit on the two upper studs, you can simply hand-thread the lower stud, then tighten all three.

7.  Otherwise it's a total breeze.

Turbo Rebuilders.
Rebuilding Turbo at a Shop.  [Query:] The wife's 940 Turbowagon will require a turbocharger replacement in the near future due to oil leak from the turbo itself and the presence of oil in the ductwork into the intake manifold. I found a shop in Rancho Cordova, CA called Volvo & Saab Auto Dismantlers (http://www.volvosaabparts.com). They have a complete turbo replacement for the above car with a 3 month warranty. They are asking for $350.00 and $35.00 deposit for the returned unit. This price looks pretty good in comparision to a new unit from IPD at $1000.00 and approximately $800.00 from Stillman Volvo. [Response 1: Philip Bradley] Your existing turbo can be rebuilt unless the bearings have worn so much that the shaft wobbles and the blades have worn or scraped the sides. The typical rebuild price is around $300. Numerous shops can do this. Check your Yellow Pages. There are also mail order shops that advertise in Turbo and Hi Tech Performance Magazine.
       Oil in the intake hoses is not uncommon. In fact, there is a drain plug in the bottom of at least the pre-1992 intercoolers. Oil drips at the turbo could be due to the oil feed or return connections. The gaskets or copper o-rings can be replaced. On the other hand, your bearings could be slowly going.  Sometimes changing to a thicker oil helps. The most definitive test is the shaft wobble test. Remove the rubber intake to the turbo, grasp the center of the shaft and try to wobble it side to side. Anything over about 1/16 inch is a sign of wear. The more the wobble, the worse the wear.   [Response 2: Gary DeFrancesco] I would agree with Philip. Make sure the turbo is not loosing oil due to dumb leaks. The oil supply and return lines can leak and make a mess. A common leak is where the oil return lines goes into the block. The o-ring here will degrade with age and heat, and leaking can be pretty bad. Sometimes poor crankcase ventilation will cause this o-ring to prematurely fail. So make sure the vent system is working properly. (Do the oil filler cap jiggle test.) A film of oil in the intercooler and associated plumbing is not uncommon. A thick/runny film is too much.
       If it is determined your turbo is dying, there are a number of options to consider. I talked with Volvo&Saab Auto Dismantlers last fall when I was looking for a transmission for one of my 740s.   The people I talked with seemed knowledgable. The used turbo they are willing to sell you sounds interesting. Do they know how many miles are on the turbo? Don't want to get a high mileage unit and face this problem again in the near future.
        There are a few places that do turbo rebuilding. I talked with a place called United Turbo in New Hampshire last year when I thought I was about to loose a turbo. They are a Garrett distributor and rebuilder. They indicated they can usually turn around in two days. Cost for a rebuilding my unit would be $300.   $400 if they felt an exchange was the better way to go. Sure beats dealer and IPD prices. The catch is, you have to R&R the turbo yourself or work with a cooperative shop.

[Response 2: Thomas] Noticing the recent messages of people rebuilding there turbo's. I thought everyone would appreciate some info on an excellent turbo builder out of Golden Colorado. I have dealt with them and also I know that the local Volvo shops use them as there turbo supplier. What you may say is so great about these guys? There turbo builds are inexpensive. I have been quoted $200-350 (roughly) for a cartridge, and $350 to $450 new complete,(don't forget your core) depending on year model and if you want to convert to water cooled.Call them for a quote to get an exact figure. I have found they are about half of what everyone else is and I know they give quality products and are the nicest people! Anyways there names are Turbocharge Engineering Corp,(303)271-3997. Hope this is helpful!  [Response 3] Try Turbo City California

Rebuilding Turbo Yourself.  [Editor]  See a complete, illustrated article showing the procedure for a Volvo turbo rebuild (in this case, a Garrett unit) at Import Car Magazine, December, 1999:  http://www.underhoodservice.com/ic/ic129934.htm

See also http://www.turbocity.com for repair kits, cartridges and rebuilt turbos.  See http://www.turbocharged.com/main.htm for upgrades and service.   Try http://www.majesticturbo.com/

Turbo Blows Black Smoke; Poor Acceleration. [Query:] While my 740T used to have great pick up with the Turbo engine, now when I push down on the gas pedal, black smoke comes out the exhaust pipe and it feels like the car is dragging or being pulled back and it stops accelerating. One of the hoses between the turbo and engine has oil in it. Any ideas?  [Response:]  Check the hoses and fittings to and around the turbo to be sure non are loose or have leaks. This can cause poor acceleration or running rich. The breather box on the intake side of the engine which is hard to get at, if clogged can cause the turbo to blow oil through its seals. If the turbo has lots of miles on it you may have a bad turbo which is blowing oil also. Don't drive with the turbo blowing oil as it will clog the cat converter! When the engine is cold you can take the rubber hose off the intake side of the turbo and see if the shaft has excessive play, or is frozen.

Turbo Blows Smoke: Overfill Oil.  I have received several messages from Volvo neophytes relating the same or similar stories: "I went to the quickie lube, where they proceeded to overfill my Turbo-engine oil by [1-2-3] quarts. Just after I started up and drove out, thick clouds of blue/black smoke came out the tailpipe. Now my mechanic says I need a new turbo. What gives?"

I am not exactly sure how to diagnose this, but let me throw out a couple of hypotheses for comment:
 1. It would appear that anything restricting the turbo oil drain would cause the unit to overfill and blow oil into the exhaust pipe. If the car were seriously overfilled with oil, this may have an effect on crankcase ventilation, probably starting at the oil breather box drain. So overfilling might clog the breather box, interfere with crankcase ventilation, stop the oil drainage from the turbo, cause the turbo to overfill, and allow this extra oil to be forced out past the turbo seals.
 2. Similar hypothesis but the unrelieved blowby increases the oil pumped to the turbo and not drained, causing excess oil in the turbo, increasing crankcase pressure, and forcing this oil out the exhaust.
If either of these are correct, then fixing the problem merely means draining the oil, replacing with the correct amount, and cleaning the crankcase breather system. Oil burning should then stop at once. Why would the turbo unit be damaged? If indeed it was damaged at all (another dealer boat payment due?) Thoughts?
[Response: Abe Crombie] The seals used in turbos are a single piston ring type seal and a labytrinth seal system. The labyrinth deal is simply slinger washers in a cavity through which the oil would have to travel against centrifugal force to leak out.  If you overfill engine the oil is restricted in draining back to the hole in side of block because the hole is now covered by oil being splashed up into the drain tube. With no easy path to drain the oil out of the piston ring seal area the oil can be passed through both the intake housing seal and the exhaust housing seal.  The flame trap/crankcase breather system being plugged has similar results.  [Response: Jim Stephenson] I believe this is the answer. My turbo was overfilled and would blow clouds of smoke. The oil was being burped up through the breather box and would run in to the turbo. Under heavy boost it would drag the turbo impeller down and shortly after that a BIG cloud of white smoke would billow out the back. After I changed the oil no more problems. But what a mess!!!   [Response: Rob Bareiss] This experience shouldn't result in a damaged turbo. Mechanical parts don't usually fail due to TOO MUCH oil...  The turbo might not pump oil very efficiently, and it could conceivably do something strange if a lot of oil hit the vanes as it was spinning at a high speed, but they're pretty tough little units.  I could see damage to a catalytic converter resulting from this. [Contrary Opinion: John O] I've rebuilt my original turbo using IPD's kit and there's a direct oil feed line running line pressure directly into the turbo unit, which then feeds the bearings. The only thing that keeps the oil in there are the seals. I've honestly never seen this happen, but I think it's possible that if too much pressure got to those seals, maybe one blew out, like the exhaust side? [Response: Dick] You may have messed up the O2 sensor at this point which will generally cause lots of black smoke, at least in my experience.

Slow Throttle Response After Turbo Replaced; Diagnosis.  [Query:] Told that my turbo was indeed in a sad state, I opted to have it rebuilt, figuring I'd save some cash. BUT, when I got it back I noticed that the car was slower. I couldn't peel out if my life depended on it.   I later found that the turbo was set very conservatively at 5.5 psi, apparently, it was sent out of town to be rebuilt, and the wastegate came back set low. The stock is (or so I have read) 7.5 psi, so I had it pumped up to 8.0, and it hasn't helped. The car is still slower than when I sent it in. When I accelerate the turbo spins all the way up past 2000 rpm, like it used to, but doesn't seem to give any boost until about 2500, at least nothing you can feel. If I start at the bottom of a hill from a dead stop and punch it to the floor, I find myself creeping uphill at a measly 10 miles an hour with the turbo spinning like mad at 2000, and suddenly I am squished into my seat at 2500.  Does anyone know what could be causing this delay between the spinning up of the turbo and the acceleration boost it provides? [Response 1: Kevin] I was told by a very reliable source (Garrett)  that the reason for a slower car with a new turbo is as follows. The old turbo probably had a lot of play, slop in the bearings, enabling it to spin up very fast, had you been running higher than stock boost, say 12psi, you probably would have noticed poor performance at the top end bacause of the slop. The new turbo is nice and tight, and there is not nearly as much slop, therefore it takes longer to reach boost, tatke it on a long fast trip, thats what I did.   I was told that a turbos bearings have to "break in" just like any other engine component. On the way there go 65, on the way back you'll be going 120 uphill.  [Response 2: Hunter] I had the same problem. My problem started one day when I was coming home and I had boost one second and the next it was gone. It was like driving a GEO!  It turned out that the actuator rod cotter pin had fallen out. My wastegate rod was just sitting there. I attached the rod back onto the bolt and put in a new cotter pin. It solved the problem. Just reach under the turbo and feel, or climb under the car and see if the rod has come off. If this is not the case it is your wastegate, or vacuums. Check all vacuums to the wastegate. You can remove the vacuum from the wastegate and plug it temporarily with a screw. Then try driving it, be very careful with boost. It could be the APC module. My problem started one day when I was coming home and I had boost one second and the next it was gone. It was like driving a friggin GEO!

How Does Wastegate Operate?  [Query:] This is the first turbocharged vehicle I have owned. My question is how can you tell when the wastegate opens and dumps excess exhaust? Does it open right before the boost gauge goes into the red? Can you actually feel a diffence it when it happens?
 [Response:] The wastegate is operated by an air actuator. The actuator gets its air from the discharge side of the turbocharger. The waste gate has a spring and a diaphragm - the spring acts to keep the waste gate closed and the diaphragm acts with pressure to open the waste gate.  The waste gate itself is simply a round hole with a cover that allows exhaust to bypass the turbine wheel when it is open.   The actuator actually has a range of pressure where it starts to open, and will be fully open at a higher pressure. You are not likely to see or feel its effects, except that it limits the maximum boost you can get out of the turbo. As boost pressure increases, the air pressure overcomes a spring pressure within the actuator, and via an adjustable rod, the wastegate begins to open.  When the wastegate opens, exhaust gasses that have been driving the turbine wheel, are diverted around the turbine, allowing it to slow down. The transition is relatively subtle, so one doesn't really feel it.
 If the actuator fails to open the wastegate, the turbo will continue to boost, and the pressure it achieves will exceed what the engine can use. The fuel system has a failsafe built into it that cuts the ground signal to the fuel pump relay during an overboost. The cause of the overboost is usually caused by the actuator hose failing.
 There is a difference between what your gage reads and what the waste gate sees for pressure.  The dash gage is connected to the engine side of the throtle body. That means that it reads the pressure/vacuum in the intake manifold. When the throttle is wide open, it will read pretty much want the turbo is putting out, however at any other position, it will read a lower pressure. The waste gate sees the pressure at the turbo outlet (for non intercooled cars) or the outlet of the intercooler for intercooled cars.

Turbo Wastegate Adjustment.  [Query:] Before I start out on my own experimenting, maybe someone can get me going in the right direction. Do you lengthen or shorten adjustment rod? How many turns in or out equates to approximately how much boost? I don't want to grenade the motor just looking for a little more kick.   [Response 1:] Shorten rod. That preloads the spring that diaphragm is working against inside wastegate actuator. If a rod comes out of the block then lengthen it a couple of rounds when you put in new engine... A couple of turns is about all you should do to not have too much stress on head gasket and other drivetrain parts. The best way would be to adjust so that the max boost in a higher gear at 3500 RPM full throttle is not more than 10 psi (70 KPa).  [Response 2: Caveat] The actuator can normally only be adjusted about +3psi. If you try to get more from it the preload on the spring will be so high that the remaining travel can´t open the wastegate properly. [Response 3:] I think that you will get about 1/4 psi per turn of the rod. However, on the 90- cars, there is a good chance that what you really need to do is adjust your throttle plate. Because the system measures the amount of air flow with the Air Mass Meter (AMM), anything that restricts the maximum air flow will limit the power at full throttle. I have found that many of the throttle plates do not open fully when the accelerator is floored.
Have someone sit in the car while you watch the throttle spool (engine off). The spool should be at the idle stop with foot off the accel. Floor the accel and check that the spool moves to the full open stop. If not, investigate to see that cable is adjusted properly and that there is nothing interfering with the accelerator pedal like carpet, mats, etc.
Remove intake hose from throttle body and inspect with strong light and mirror - it should be absolutely clean inside. If not, remove it and clean it. Check that when closed and held up to light, there is a nice even ring of light around the throttle plate.  With throttle body installed, floor accelerator from inside the car, and inspect to see if throttle plate is EXACTLY parallel to the bore - i.e., fully open. Even a slight deviation from this position will rob a lot of power at full throttle.
If it is not fully open, remove the throttle link and carefully bend the throttle shaft lever toward the front of the car. Just a little! This will effectively shorten the length of the lever and the same amount of movement of the throttle link rod will move the plate further. Check it again and repeat until it opens fully. Note that if it opens more than full, it will rob power just as if it didn't open fully. Dirty injectors are another source of lost power. All injectors must have good patterns and equal fuel flow to keep the power balanced between cylinders for best power, performance, and fuel economy.
Lastly, if you wish to increase boost, I highly recommend that you either use the Volvo "Turbo +" kit which will adjust the boost curve so that you do not get too much boost at low rpm, and give you higher boost overall, or install the Saab APC system (see the directions on the Turbobricks site). Simply increasing the boost with the control rod will increase the tendency to predetonate or ping, and the control system will back off the spark advance  negating any gains you might have made. There are also lots of other things that might be going on that can be mis-interpreted by the knock sensor as predetonation with the result that the timing is backed off and you get less than maximum power. It would be wide to check the engine thoroughly to make sure that everything is working properly. Also, be sure to use high octane gas, and if your area adds methanol or MBTE, I recommend use of a fuel additive like AMSOIL PI to keep the fuel system clean and improve the performance of the fuel.

CBV Valve Operation. Garrett Turbos.   [Query:] I was working on my engine last night and I thought I should check the one way valve on the CBV  (compressor bleed/bypass valve)for proper operation. I checked the operation of the oneway valve and it was on backwards, meaning boost pressure was being forced into the CBV. I turned the valve around and took it out for a drive. It bleeds now, but it does it almost all the time while in normal aspiration mode.

1. Is the valve destroyed?
2. I noticed I can adjust the valve. Is it worth doing this or should I go buy the Bosch plastic valve and replace it?
3. How should I adjust the valve to get it to only open at max vacuum?
4. One the one-way valve has been opened and vacuum has opened the CBV, how does it close back up? The one-way valve would seal off and not allow air to go back in to re-pressurize the CBV, right? I am having a difficult time understanding how air would re-pressurize the thing.
[Response: Abe Crombie] That check valve should be installed so that it can pull vacuum on the bypass valve. This is so that on deceleration when the manifold vacuum goes up it opens valve and allows the diaphragm to be moved upwards opening the valve and allowing the boost trapped on lifted throttle to in effect re-circulate in outlet
 plumbing of turbo.  The valve would prevent the boost from reaching the diaphragm of bypass valve when installed properly. The check valve allows vacuum to be pulled and the check valve has a controlled bleed in the reverse flow direction to allow the diaphragm to close in a dampened manner.  Reverse check valve and see if all is okay. If it is then nothing else needs to be done. If not you will have to replace the bypass valve.
Mitsubishi Turbo Note. [Query]  Does my '89 740 Turbo Wagon with Mitsubishi turbo have this "check valve"?  I know it has a "valve" on the turbo (Bypass valve) but I'm assuming that there's also supposed to be a vacuum check valve on the line between that bypass valve and where it connects to the intake manifold?  [Response: John Armero]  The Mitsubishi turbos on the late 700 cars do not have the "vacuum check valve".

Excess Crankcase Pressure in B230FT.  [Query:] There seems to be excessive crankcase pressure in my engine (B230FT) I've checked the ventilator under the intake manifold, it is not plugged. Is this the only relief the engine gets from the pressure buildup. What is causing this pressure, the only reason that comes to mind is bad rings. From reading postings it seems that a negative pressure is the norm.
[Response:] I have seen plugged oil traps. Make sure that the oil trap isn't plugged by blowing through it with the oil cap off. Hook a hose to the oil trap where the flame trap goes. Any compression loss into the head or crankcase will cause excessive pressure.  [Response 2:] Excessive crankcase pressure is often the result of bad/worn piston rings, or worse; broken piston ring lands (ring lands is the part between piston ring cutouts on the piston).  The main reason of this fault is detonation/knocking...  To diagnose this problem; take a dynamic combustion pressure check.
Turbo Oil Breather Box Notes:  See the link for more detailed information.  Also see Michael Ponte's excellent description and illustration at http://www.mikeponte.com/volvo/oiltrap.htm

Normal Oil Consumption for Turbo.  [Query:]  What is the normal oil consumption for a turbo engine?  [Response 1:] Based on a highly non-significant sample size of 2: my friend with a 245 Turbo says that he levelled out at one quart per 2,000 miles, and that this rate of consumption remained the same from 80,000 miles until he sold the car at 150,000-plus miles. This is the same rate of consumption as my 744 Turbo with 91,000 miles, so I say that 2,000 miles per quart is healthy for a Turbo motor.  [Response 2:] My 87 764T w/187k miles uses zero quarts amsoil synthetic 20W/50 in 10,000 miles, I change the oil and AMSOIL ASF-42 filter every 10,000 miles.   My 90 744T w/83k miles uses zero quarts amsoil synthetic 20W/50 in 10,000 miles, I change the oil and AMSOIL ASF-42 filter every 10,000 miles.
I also ran a spectrometric oil analysis comparison on wear metals using dino oil at 3,000 mile change intervals and oil samples with synthetic every 3,000 miles to the 10k oil change interval I have settled on. On my engines, the dino oil accumulated more wear metals, had lower residual alkalinity (total base number or TBN for any lube engineers out there), and increased it's original SAE rating by 5-10 points with regard to the synthetic at 10,000 miles. The only reason I change the synthetic at 10k is that I do get carbon particulates (soot) buildup to .5%, the buildup curve turns the corner at around 10-11k (it runs 0-0.4% for the first 8-10k but then climbs quickly...I chose to dump at .5%----BTW, this stuff is so fine that a micron bypass filter won't clear it out past 15k...I've tried AMSOIL bypass filter and while it clears the oil it won't take out the soot.) I believe the soot/carbon particulate buildup is characteristic of the turbo gas engines, inasmuch as my experience is duplicated on my Saab 900t, both the 84T (RIP) and the current 87 900T. I have no experience with turbo diesel engines, but maybe their soot particulate size is somewhat larger than gas engines.
That's not to say either engine has NOT used oil....but when they do, I have invariably found the problem to be an oil LEAK, front or rear main or cam cover gasket. Once the 740t leaked at the turbo oil return gasket at the block and also at the oil filter adaptor. Have also had oil leaks at the distributor on the rear of the hear....but all fixed relatively cheaply with Volvo O-rings.  Point is these engines are really good on oil control IMHO.....but they are also b!^&hing leakers!
[Response 3:] my '87 740T with 178,000 miles runs on dino oil. Lately the oil consumption has been 1 quart in about 2700 miles. Since I usually change the oil at 3000 miles, I don't bother adding the oil. I have been just changing instead.  Can't tell you anything on how much my '88 740T consumes. It has been a leaker since I bought it last spring. The oil return pipe from the turbo leaks at the block. Maybe 1 quart in 400 miles. I can see it leaking and dripping when the engine runs. Just recently cleaned the throttle body and crankcase vent system. Maybe this will help the problem. If not, I will have to repair the leak with a new o-ring. OTOH, with all that oil dripping and blowing under the car while driving, a good part of my undercarriage is coated with oil, it will never rust.
[Response 4:] My (brief) experience has been 0 quart consumption. I run Mobil-1 10W30 on my 1992 944T with about 80k km (50k mi).
[Response 5:] My wife's '91 940 Turbowagon that has 102,000 miles on it goes through a quart of Castrol Synthetic 10W-30 every 2000 miles. This number seems to coincide with what you have stated. The Turbowagon is in mint condition without a single spot of oil leak on the garage floor. I have pulled all the plugs to check their condition and there is no evidence of oil in the combustion chamber. The exhaust pipe is also quite clear without any residue or smell of burned oil. I am just amazed with this 940 Turbowagon and the ride fells like new.
[Response 6:] I change my synthetic oil as close to every 3k as I can. The longest interval was just over 5k. I'm not into the turbo a lot, generally I nail it once a day getting on to the highway. This is an '84 with 160k and it uses no oil worth writing home about. Honest.

Oil in the Intercooler.  [Query:]   When changing my radiator (91 940 137,000 miles and new to me)I noticed black oil in the air hose from the turbo to the intercooler. Is this normal? Or do I have problems?  [Response:  RandyS] It's normal, don't sweat it! Unless it spewed out a quart, I'd say you are doing OK.

Gasoline Recommendations for Turbo Engines.  See the link to the Fuel and Lubricants file.

[Other related comments:]  . I could pick up some pinging on 87 octane when boost was up, thus switched to 89 and things are much quieter. I'll even go to 92 octane when I know I'll be up on the boost gage.  [Another Response] My 1990 745T runs fine on 87.

Turbo Expiration. [Query:] Does anyone know what a turbo sounds like when it starts to die? does death usually come slowly, or suddenly. will the car run without it, and if so, for how long? [Response:] Some die slowly, losing output gradually as the engine ages. Others begin to make noise (scraping or rattling), especially under load or when very hot, that may signal that the impeller blades are touching the housing (or have been bent through the introduction of a foreign object), or the bearing is about to go south. Others fail through seal failure, dumping oil out the exhaust. I have been told that turbos can fail without any warning whatsoever, but I would not expect that. Your car should run without the turbo, but you will be driving a car with something like 80-90 horsepower because of the reduced base compression ratio on the turbo cars. In other words, maybe okay to limp to a garage, but no for everyday use unless you are a glutton for punishment. If the car is throwing oil out the exhaust, do not drive it at all. You may be able to clear a little out, once the turbo is rebuilt or replaced, but if you get too much into the exhaust you will be buying that as well.

Turbo Oil Leaks.  [Query:] 740T leaks oil out the oil filter adapter and turbo return line

Flametrap and Crankcase Pressure:

[Gary DeFrancesco:]  Before going too crazy, make sure you have good crank case ventilation. Do this by running the "jiggle test". Loosen the oil filler cap with the engine idling. If it feels like it is being sucked down on to the valve cover or is only slightly jiggling, then you are probably okay. It the cap is dancing, then you have some positive pressure in the block which needs to be corrected. [Editor's Note: See  Excess Crankcase Pressure ]

Sources of Leaks:

[Tips from Gary DiFrancesco] Turbo cars do have some common leak points when the age and mileage build up. There are two places I would check right off. First check the oil return pipe going between the turbo center section and the block. Where the pipe goes into the block, the o-ring at this junction can and will break down and oil will blow out here (even with good crank ventilation) and run down the side of the block. The other leak point is from the oil cooler adaptor. You know about the o-ring between the adaptor and the block, but there is another o-ring in the adaptor assembly. One or both of these o-rings will also start to leak eventually.

[Query:] I have a 88 760 Turbo with 226,000KM on it, losing oil.  I am going to look at it this weekend and would appreciate any suggestions on what tends to leak most on these engines. I don't really notice any oil onthe driveway from where I park and it doesn't seem to burn oil. .  [Response from Michael Jue:]  Oil leaks on B230FT -

    Oil blowby due to worn valve seals OR clogged flametrap housing (no actual flametrap, just the housing - part of the EGR system; located directly beneath #2 & #3 intake runners. A real knuckle buster.)
    Oil leaking (weeping) from oil filler cap - Either bad gasket on cap and/or clogged flametrap housing. The clogged flametrap creates high crankcase pressure forcing oil by the gasket.)
    Oil leakage past turbo bearings - a fairly likely cause at 226k Km; imperceptible in exhaust (absence of blue smoke).
    Rear main seal - not as likely but possible (changed mine twice in 255k miles); check for inordinate build-up of oil on transmission
    Front engine seals (cam, crank, idler) - pull the top half cam cover and inspect timing belt for oiling; change if any sign of oil contamination and replace the seals at the same time. (Recommend changing them as a complete set with your timing belt change as the belt must come off for replacement of any of the seals anyhow.)
    The old oil filter gasket was left on the oil filter adapter *face* when installing a new oil filter.
    Any combination thereof or all of the above.
    [Christopher Rowat:] One other possibility for oil leaks is the oil filter adapter gasket, a little O ring that seals the oil filter adapter to the block.
Oil Cooler Adapter Leak Repair:

[Response 1:]  The o-rings in the oil cooler adapter will compress and harden with age and mileage. They are only a couple of bucks a piece and should be replaced when they start to leak. They are not hard to replace, but it will take a little time in order to move things around so that you get access to the big bolt holding the oil cooler adapter to the engine block.  [Response 2:] The oil cooler adaptor had 2 large o-rings that compress and get hard with age. After awhile, they start to leak. The o-rings cost about $2.00 each but are a bit of a PITA to replace. You have to remove the whole adaptor, and the best way I have found is to remove the power steering pump from its mounting bracket. The pump can be left in the car, just remove it from the bracket. This will allow you to move the pump out of the way so that you can get a big wrench on the big bolt that holds the adaptor on the engine. Once off, the two parts of the adaptor are separated with the removal of the big nut just below where the oil filter screws on. You need a deep socket of large diameter to do this, but I forget the socket size. (Make sure you mark the adapter parts so that you can reassemble it in the same orientation.) Replace the two o-rings and put everything back together and this leak is no longer a problem assuming the o-rings don't slip out of place during reassembly (use some grease to hold them in place).

Oil Return Line Leak Repair:

The leak in the turbo oil return line again is due to a failed o-ring. The oil return pipe in the turbo will start to leak where it enters the block. The proper way to fix this is to remove the pipe from the turbo center section and remove the pipe. The ring is cheap, but replacing it can be a real PITA. Before attacking the turbo oil return line leak, I would check your crank case ventilation. If the ventilation system is not working perfectly, the pressure build up can force oil out the turbo oil return o-ring. Replacing the o-ring may not solve the leak entirely, so fix the ventilation first. Once fixed, you may find the leak is gone or at least greatly reduced. In which case, it may not be worth going through the pain of replacing a cheap o-ring. Maybe a good cleaning and degreasing of the pipe and surrounding area followed by a careful application of Permatex blue sealant will hold the oil at bay until such time the turbo needs attention. The o-ring can then be replaced as part of the turbo servicing.

Unless you are successful in removing the two screws/bolts that hold this pipe to the turbo center section, the only other way to replace this o-ring is to remove the exhaust manifold/turbo assembly. Unless you have to repair the turbo, I don't like to go there.

Replacing the gasket at the turbo end and the washer at the block end should do it. However, this too can be a real PITA since the bolts on the turbo end can be sticky and there is not much room to work. Also if the pipe is not inserted into the block properly, it will leak again. But if you can get the two screws off, you have to twist and turn the pipe to pull it out of the block and off the engine. Once off, clean up the parts and install a new o-ring and gasket. Put a little grease on the o-ring to help it go back into the block. Now twist and turn it to get it to back into position. (Probably want to practice this without the o-ring and gasket before actually doing it.)

Quick and Cheap Fix. If you can't get the pipe out (since some previous grease monkey stripped the socket on one of the cap screws on the turbo end), then you can always seal up the leak like I did.  I completely cleaned the area around where the pipe goes into the block. I used a strong degreaser to clean the pipe and the surrounding area. I even used Q-tips soaked in degreaser to get inside where the pipe goes into the block. Once everything was surgically clean, I dried the area with a warm heat gun. I split the new washer so that it could be placed around the pipe. The washer was coated with Permatex Ultra Blue sealant, and some of the sealant was also injected into where the pipe enters the block. The coated washer was then pushed into this space and sealed into place with even more sealant. It is a bit of a patch job, but it is working just fine. No leaks in the year since I did the job and it is cheaper that screwing up the turbo.  Before I fixed this leak, I was loosing a quart of oil in less than 500 miles. Since the repair, I am estimating over 5000 miles per quart. Hard to tell for sure since I change oil at 3000 mile intervals.  Those are the leaks I am familiar with on the B230FT engines.

Turbo Oil Return Pipe Seal Replacement.   [Query:] Just replaced the turbo in my 740 wagon. Everything seemed go smooth except the turbo oil drain on the bottom of the unit. After I first drove it, I noticed oil all over the bottom of the car, as well as a huge puddle on the ground. For those who don't know, the return pipe just sits in the block against a rubber gasket/washer. Since then I tried using RTV gasket maker from Permatex, past day seems to be fine. Anyone know of a way to assure that the oil return pipe sits tight in the block?
[Response 1: Paul S.] Sounds like the rubber seal wasn't centered/seated properly. It happens. I assume you used a new seal.  I coat the rubber thing with synthetic grease and have an assistant position the turbo, whilst I guide the return tube nicely in the hole. Seems to work for me, but I think it's a lousy design.
[Response 2: Don Foster] The pipe doesn't really sit against a gasket on the block. The O-ring, on the pipe, fits INTO a hole in the block (and can get distorted, bent, cut, skewed, screwed, blued, and tattooed) in the process. As Paul pointed out, maneuvering the turbo, pipe, and O-ring into position can be a challenge.  Here are three thoughts: That tube is only a gravity-fed drain -- there's really no oil pressure there, so there's almost no driving force to push oil out. O-rings get there sealing properties from the "squeeze" against opposing surfaces. In this case, those surfaces are the tube and ID of the hole in the block. You shouldn't need to push it down solid to achieve a seal. Even so, you might get a few thousandths extra insertion, but I'd guess the manifold and turbo is already down all the way. After all, it weighs a lot, so would have sat low during installation.  Also, does your engine have very high crankcase pressure?
[Response 3: Johnb]  The O-ring must be inside the hole in the block and BELOW the ridge on the tube.  I've found the easiest way to do this when doing a turbo replacement is to bolt the exhaust manifold up loosely, and THEN install the drain tube to engine block and drain tube to turbo lightly. Torque up the manifold and then tighten the turbo drain gasket bolts.  Replacing the gasket/O ring with the turbo bolted down tightly can be done but it's a close thing.
[Response 4:] How to deal with oil leaks on the turbo oil return pipes? The '88 leak is worse than the '87 and I did get the new sealing ring and gasket to repair this leak.  Replacement involves removing the oil return pipe from the turbo.I have replaced several of these oil return line seals - never had a problem getting the tube flange bolts out of the turbo housing. You will have to jocky the tube around a bit to get the bottom end out of the block. Be very careful getting it back in with new seal - it is easy to pinch the new seal even after lubing with synthetic grease. I usually keep an extra seal in my tool box in case I pinch one during install. And after install, use inspection mirror and strong light to check to make sure that it went in properly!

Turbo Oil Return Bolts.  [Query:] I removed the turbo oil return tube the other day to replace gasket & seal. Got the parts, went to install them, now it seems the bolts that go into the turbo are too long, they bottom out.  [Response:  Paul Kane] The bolts in that area LOOK the same - but they ain't. Just a 1 or 2 thread difference can cause a 'bottom out' .  You may have swapped 1 or 2 and didn't realize it.

Remote Oil Filter O-Rings.  [Query:] What should I be prepared for with regards to a leak where the remote  oil filter mount mounts to the engine block?  [Response: Nick Choy] I just went through this little "challenge" myself. Evidently, the rubber o-rings (there are two) that are sandwiched between the filter adapter and the block crack as they age. I tried to remove the adapter myself to replace these pesky seals only to find that once I was past the large threaded tube/filter-mount fitting, I was blocked by a press-fit return tube to the front of this adapter that runs out of the side of the block. At the time (about a year ago) I was able to only fit my finger between the adapter and the block, and so I cleaned the rings as best I could, loaded them up with RTV sealer, then tightened the whole thing back up again.
About a month ago, I noticed it leaking again, so rather than face the same frustration of last year, I just gave in and dropped it off at my local Volvo-specialty mechanic. Two hours and $86 of my money later, he had changed both o-rings, and the two crush washers on the oil cooler lines. They told me that these o-rings need to be inspected periodically, and replaced every so often due to extreme heat and constant oil baths shrinking and cracking the rubber (duh!).
Needless to say, if you're willing to fight with the tubes and lines down there, and get the two o-rings and brass crush washers for the oil cooler lines from your local auto parts store ahead of time, then I say go for it! Otherwise, you can wimp out like me and just drop it off at the mechanic!
[Tip from DaveS]  The wrench for removing the oil filter adapter/mount from the engine is 32 mm, and the wrench needed to separate the halves of the mount is 30 mm DEEP. I cheated and used 1-1/8" (don't ask) for the latter and it worked.

Lack of Turbo Boost. [Problem: Lack of Turbo Boost.] Thanks to Steve, Paul, George, Doug and Robert for giving me the help in troubleshooting my lack of Turbo Boost.

The Turbo itself spins smooth and there is virtually no end or lateral play. The Oil Accumulator that has been on this thing since day one. The tests made with the new boost gauge placed in-line before and then after the throttle plate confirmed the problem and it was seconded by the removing of the plug in the catalytic converter housing. The cat is plugged tighter than a crab's ass. So now I need a new cat and with that new pipes.

[Another comment:] That's exactly how I got my turbo wagon cheap -- the PO had a new turbo installed (lucky me!) and then, 5000 miles later, it wouldn't go into boost. She thought the new turbo was toast and junked the car in frustration. [Another comment:] I am experiencing similar problems with no turbo boost on my 83 240T. When I bought the car, the turbo was leaking oil like a sieve. I replaced it, and boost was a little better, but just a little. All the other usual things were done such as new plugs, wires, filter, vacuum lines, etc. Still barely getting boost. After reading the posts on BrickBoard, I began to suspect the catalytic converter. I removed the test plug and noticed a lot of pressure from the opening. Drove around for about a mile without the plug, and had a little more boost. I then had car checked a reputable independent Volvo garage, and they confirmed that cat was so plugged it almost "broke their gauge".[More diagnostic comments:] Before you get too carried away, note that at steady state - i.e., constant speed on level ground at 3K in second gear, there will be relatively little boost measured at the MANIFOLD. If you are measuring the boost on the high side of the throttle plate, then it is likely that you have a problem. But if you are measuring the MANIFOLD pressure, then try starting at 3K and flooring it. You should see the boost climb to ~8.5psi until you pass 3700 rpm. Then the boost should jump to about 10.5 psi as the IBS valve opens. IF the boost does not climb smartly and jump quickly at 3700 while you have your foot to the floor, then you have either an intake obstruction, turbo going south, stuck/broken waste gate or waste gate controller, or clogged cat.

Remove the plug at the top of the car, just behind the turbo exhaust housing. Try it again:

noticeable difference indicates clogged cat. No difference indicates turbo, waste gate, or intake plumbing obstruction.

Remove intake line from front end of turbo. Use your fingers to wiggle turbo shaft and spin it. Should spin freely and smoothly, there should be SOME lateral play, but NO contact by impellers on housing.

Turbo Overboost.  [Query:] Today I experienced something strange, the turbo seemed to be overboosting. I was on the freeway and accelerated to pass another car, it felt as though I had gained 50 more HP. I looked at the boost gauge and the needle was past the end of the boost indicator.  Worried I would toast something or send parts flying, I kept off the accelerator for the most part. It definitely felt and acted like the turbo was working overtime. The car was parked for about two hours, and did not misbehave again. I have no idea what my boost pressure is running, but my last gas mileage check was at about 21mpg(mixed hwy/city driving).   Anyone have any suggestions on what to expect next, where to look, what to do?  [Response:] Check to see if the actuator hose is split or broken off. That will not allow the actuator to open the wastegate, causing the overboost.

Turbo Loses Performance at Boost.  [Query:] In my 760 with turbo and intercooler, when trying to accelerate quickly or when  driving up a large hill I lose performance the more gas I give it and it blows black smoke out the back. The turbo needle is about at 11:00 when this starts  and never seems to get past 12:00. I have not been able to get more that 4000 RPM's out of this car at all except maybe in park.  [Response:] Find the leak in the pressure side of the turbo.   Mine happened to be in the bypass valve...allen screws back out.   It could also be a leaky hose or clamp or leak/hole in the intercooler ...somewhere your engine isn't getting all the air being blown into it and your dash gauge is showing it! The AMM thinks 9 lbs of boost is being fed to the engine and gives the ECU/Injectors the fuel...since a lot less than boost is getting to the  engine, you blow black smoke/overfuel.   Could also be fuel pressure regulator, but unlikely since it idles, apparently.

740T Has Weird Deceleration; Anti-Stall Valve Hose.  [Symptoms:] Our '87 740 turbo has recently begun behaving very strange.  Acceleration is fine, normal running is fine, but if you lift off the throttle after
acceleration (with boost), the car jerks once and a "hiss" can be heard from the engine.
[Response: John Binford]  '87 7xxT's had an anticompressor stall valve......about a foot beyond the turbo, close to the fan.  If the hose to the valve is off, it won't release and you'll get compressor stall and maybe the excess pressure can 'hiss' somewhere. The diaphragm in the valve can also die/hole, in which case it won't release either. Check the valve for proper hose to it and operation.

Turbo Has Power Loss and Cherry Manifold: Knock Sensor.  [Query:] My 740t intermittently looses power and the exhaust manifold turns bright red.  I don't know if the two are related but when the car was in the loss power mode I opened the hood one night to check for arcing wires and I noticed the manifold glowing.  [Response: Abe Crombie] Those are the symptoms of a knock sensor problem. The knock sensor may be bad but more likely the connector is the problem.  When the ignition control unit detects no input from sensor the timing is retarded which is the safety from excessive spark knock but this does make engine power suffer and the delayed timing sends exhaust gas temp skyward.

Poor Idle: Turbo Intake Gasket Leaks.  [Query from Joel Eisner:] Rough idle with some lean backfiring but it holds at 900RPM.   Diagnosis steps: I am about to give up and part the thing out if I can't fix the idle. I would like to keep the car but it is driving me crazy.  Clues?  [Response 1:  Joel Eisner] I found the problem. I pulled the intake manifold and about an inch of the gasket around the #4 cylinder is missing with obvious signs that it has been gone for a while. That area was black.  {Response 2: Warren Bain] The gaskets go quite often on the turbos. Mine went and the idle was very rough. A quick replacement and all was well. It's quite easy.

Intake Manifold Gasket Leaks.  The turbo is prone to intake manifold gasket leaks, (so I hear) and mine was no exception. The WD-40 spray test showed much leakage. I used a cheapo gasket (stiff type), put it all back together and voila - NO difference. I tried again with a high quality (rubbery (nitrile?)) gasket and used permatex liquid gasket sealer (although there are various views on sealer use) and voila - BIG improvement at idle. Lesson - use high quality gaskets.

Exhaust Manifold Gasket and Studs.  [Query:] My 744ti currently has 184,000k mi. It is leaking a little at the exhaust manifold so it is time to replace the gasket. I have noticed that it looks like it is the original gasket. I am thinking about replacing the studs and the on the head when the gasket is replaced. Is this a good idea or am I wasting my money. I want to do the job right from the beginning.  [Response: Rob Bareiss] I always recommend replacing all the exhaust nuts, and to try to save the studs I split the nuts with a chisel. This can save a great deal of aggravation (it's an old VW trick- the studs on VW heads always broke).  [Another philosophy from: Onkel Udo] You might want to spray the studs w/apenetrating oil repeatedly for the preceding days.  When you reassemble, use antiseize compound on the new studs and coat the exposed areas with a silicone spray or a grease of some type.  There is nothing more annoying than trying to remove rusted-in-place nuts on exhaust flanges knowing that at least one stud is going to shear off no matter what you do.   [Response: Don Foster] If the original studs appear "eroded" (rusted away) and you think you can remove them without snapping even one, then new studs would be a cheap investment. I dearly love my oxy-acetylene torch. Every time I use it, I kiss it. You might also consider replacing the big O-ring in the oil cooler adapter at the same time -- they age, dry out, crack, and start leaking at about the 10-year point with your mileage, and are a B*ITCH to get to -- but with the turbo out, the area's wide open, and access is much easier.  [Response 3:  John B ] wouldn't fix the stud problem if it's not a problem.   OTOH, if you break one stud in the process, might as well replace them all.   I think IPD has a stainless steel stud/bolt kit?
When you pull out the manifold/turbo, then's the time to replace the turbo/tube and tube/block gasket and O-ring.  Even if you don't pull the entire manifold/turbo out to replace the exhaust gasket (best case) the turbo oil tube is a lot easier to reseal with the manifold loosened (and the two bolts holding it onto the turbo removed).
How's your 02 sensor? It's easy to get to with the manifold out.

Broken Turbo Exhaust Stud.  [See also the section under Exhaust:Exhaust Manifold Gasket and Studs Replacement] [Query:] I have an 86 760 Turbo that was rebuilt about 15,000 kM ago. The problem is that one of the exhaust manifold bolts has snapped off and when the turbo is under boost, it whistles.   I think it is on number 3 cylinder and of course the bottom bolt. Is this leak going to harm the exhaust valve over time?  I was also thinking about the doing the work my self and was wondering if anybody out there has had success with replacing exhaust studs with the head on? I really do not want to pull the head but I think it maybe the easiest way to get the stud out. My biggest fear is breaking off all the studs in the head. The head was rebuild when the engine was rebuilt so I am hoping all the studs have anti seize on. What should I use on the new bolts for anti-seize?  If I remove the head do I need new head bolts??? I got the specs on torques for the head but what torque do I torque the exhaust manifold too, I think they recommend only about 30 Ft-Lbs? Is this right?
[Response 1:] Look at the bolts that hold the bypass valve on the pressure side of the turbo. This is the valve on top and in front of the turbo unit with the vac. hose leading to the intake manifold. These bolts can loosen slightly and allow boost pressure to leak. It sounds like a whistle when under boost. When I first heard this on my car, I thought I had a turbo starting to die.  Fortunately an honest service manager at my local Volvo deal went straight to the bypass valve and showed me the loose bolts.
 [Response 2:] A broken exhaust manifold stud and failed gasket usually make a significant exhaust "putt-putt-putting" sound. I would never describe it as a "whistle". You might have a failed hose or coupling on the high-pressure side of the turbo, and you're hearing air escaping.  A broken exhaust manifold stud can absolutely be drilled out and tapped without pulling the head -- and I would certainly try drilling/tapping in-place before taking that next expensive, difficult, and time-consuming step. I did exactly that on my '82 240 turbo (non-intercooled) which had two broken studs (from totally incompetent repair shops). A very useful accessory was a right-angle attachment for my electric drill and several shortened drill bits.  Drilling and tapping in these conditions assumes some experience. Incidentally, if you try an "easy-out" you'll likely break it, then you'll be grinding out the very hard piece with a Dremel, probably with the head off.  You probably want to soak the nuts/studs for 3-4 days to loosen the rust. Kroil or PB Blaster seem to work well. An oxyacetylene torch is an almost essential tool for this job.  BUT..... This is a job only for the experienced shadetree mechanic. Pulling the turbo is not difficult, but reinstalling it is a task.  [Contrary Philosophy from Rob Bareiss]  If you do break a stud, get ready to pull the head. Don't try to fix exhaust studs in place.
Stud Removal Tips [Paul Seminara]  PB Blaster.....soak, smack area near thread with hammer, PB Blaster, soak, wipe, heat, PB Blaster, hammer smack, extract with two nut method, tighten a bit, then loosen a bit, more PB Blaster...etc, ...repeat..patience is really the key, because you do want to save the stud!! When you have it out soak again in PB Blaster, clean and brass brush it, smear with a good Ni or Cu antiseize for future removal. If one is broken (I really hope you didn't install the turbo with broken stud(s)...it just would have been sooo much easier on the bench)...do the above if there is stud sticking out, if no threads use locking pliers..
If in deep first try a left hand cobalt drill bit, a "cinching stud remover", diamond bits,etc GOOD LUCK.  Under no circumstances should you use an Easy-Out or other stick in hole and simply twist stud remover (unless of course you know the stud is loose, but in that case your left hand drill bit would have taken it out) Why cobalt? Normal hardened HSS, or even the TiNi drill bits won't touch that stud!!

Turbo Exhaust Stud Replacement. [See also the section under Exhaust:Exhaust Manifold Gasket and Studs Replacement] [Query:] Is there any reason not to install 3/8" exhaust stud in lieu of the 8 mm that seem to sheer off. Are there higher strength 8mm studs available?   [Response] Stainless studs are an excellent idea for aluminum heads.   Try to find a local fastener supplier that offers high-strength metric studs  (8mm x 46mm: (std pitch, 1.25mm), 45mm long with approx. 15mm thread on one
side (head side), 25mm on the other and 5 mm of no thread.).  Always use anti-seize on all studs.  Search yellow pages under nuts & bolts.
[Response: Jeff] Open up the manifold holes and the holes in the head. Retap the head for 10m-1.5 size bolts. Use 10mm Allen Head Cap Screws to secure the manifold to the head.  You will have to open up the holes in the gaskets as well to make them fit. This is about as bulletproof as you can get.

Turbo Hose Preventive Maintenance. [Tip from Simon Eng]  If your car is equipped with a turbo, please inspect the rubber air hose from AMM to turbo. This is the one that is about 3" in diameter and is in the form of an elbow about 12" total length with two small connections on the side.  Pay particular attention if your car is over ten years old. (Mine is 15 years. The hose is original.). Inspect the end that is connected to the turbo inlet. Due to the extreme temperature at this location, the rubber deteriorates and actually melted in my case. It is probably leaking air into the turbo (free air!).  Cost is over $100 for parts. [Response: Rob Bareiss]  Any and all of the air hoses on a Volvo turbo can leak, with two rather unpleasant consequences:
 1) The car will run like crap
 2) You're going to have to spend some money
The usual cause is oil attacking the rubber from the inside out. Some of the hoses are REALLY expensive. The large S shaped one is about $180 list price. The one just before the throttle body is $80-$120 depending on which model you've got. The little one right at the intercooler is only $10. The silicone high-temp L-shaped hose at the turbo is over $100.
It's probably a good idea to periodically look inside one of these hoses to see if there is any evidence of oil. If they're wet inside, you've got a turbo leaking oil, AND sooner or later you're going to need to replace these hoses.  The only good news in this is that you'd be pleasantly surprised at how well duct tape can seal up one of these, and how long it can last...  And it's a LOT less than $180....

Turbo Hose Sources.  [Query:] I'm looking to replace the original turbo hoses. All are either really soft and/or showing signs of interior deterioration. The only problem now is that my dealer's prices are about ten times what I'd expect to pay for these hoses. Does any one know of a cheaper source for such hoses? I'm thinking of just buying some straight 2" ID silicone hosing from one of the many turbo outfitters for the short hoses that come off the intercooler. However, what should I do about the 90 degree bent hose that comes directly off the turbo outlet?  [Response 1: Don Willson] I just bought a set from an independent parts house for my '89 760Ti.  The short silicone was $24.25 pn 127-6963   The fresh air hose air filter to turbo input was $127.42 pn 138-9648  The slight "S" outlet turbo to intercooler was $47.12 pn133-6815  Mine were failing, not from turbo heat but from exposure to the radiated  heat from the exhaust. I found some aluminum tape with high temp silicone adhesive and wrapped around them to reflect some of the heat.
Silicone Hoses.  [Tip:]  For a source of silicone hoses for turbo intercoolers and other applications, see: http://www.bakerprecision.com/silicone.htm
[Tip: Robert Haire]  Baker silicone will fabricate (long lead time) the super fuel resistant fluoropolymer lined stuff. Paul S. and I use the regular Samco stuff from Pegasus Racing with fine result. Prices for elbows are $35 vs. Volvo $150 and for short straight pieces, cut them of your old elbow.  High temp RTV does a great job of gluing pieces if you have to extend elbows or make reducers, etc. Alternatively, go to a truck facility and ask for their turbo and heavy duty coolant hoses. They cover the sizes you need at much lower cost.

Turbo Hose Clamps.  [query] I really have no problem with ordinary hose clamps for the cooling system. As long as they are not overtightened and they are monitored, they seem to work fine and the hoses will "go soft" or otherwise croak before the ends are damaged by the clamps. Not so for the turbo hoses unfortunately both the silicone and rubber hoses and that infamous "oil mist"..seem really hard on hose ends. Cheapie clamps chew the crap out of these expensive hoses. My one gripe about the Volvo hose is: they are rather narrow.  [Response: SRinglee] The ONLY clamp to use is the Breeze Liner Clamp, all stainless with a smooth liner under the perforations to avoid the common cut hose phenomenon.  They are especially made for silicone and softer hoses, but work well for cooling system hoses as well.  See:   http://www.breezeclamps.com/prodline.html  for product line information.
Costs around $1.50 per clamp in the common Volvo sizes. I just bought some from DNA Parts at: dnaparts@dnaparts.com

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