Exhaust                                                                                                                  FAQ Home
  Volvo Maintenance FAQ for 7xx/9xx/90 Cars                                                                                                                     Version 5.0
Oxygen Sensor Replacement

Exhaust Manifold Leak

Exhaust Manifold Gasket & Studs Replacement

Catalytic Converter Diagnosis

Replacement Converters

Exhaust Replacement: Brands

Exhaust Replacement: Procedures

Exhaust Brackets Keep Breaking

Exhaust Smell: Leaking Injector Seals?

Oxygen Sensor Replacement.
Opening Caution. [JohnO] If doing it yourself, do it with a cold engine as many O2 sensors are more likely to cross-thread if done hot (although not so much so with Volvos). If you doubt your skills with this, just take it to dealer and pay them to replace it as it won't be that much for the labor (about 1 hour).

Tool Notes.  Which tool do I use to remove the O2 sensor?  [Paul Seminara]  Us a crows foot or special slotted O2 sensor socket or "adapted" open/closed end wrench.

Replacement Procedure.  [Editor: Tom's notes apply to a 960 but the procedure is similar for 740/940]  [query] I'm planning to change my O2 sensor on my 960 wagon.  Where is that thing? How tough of a time will I have in removing it because of heat-related seizing.   [Response: Tom Irwin]  OK, if you are w/o a shop and hydraulic lift, I recommend the following...  FOUR JACKSTANDS Rated to 3,000 pounds apiece or better. I've been lifting the car under it's mid-chassis reinforcement with a large wide-saddle jack. A skinny jack will damage the underside of your car...  Lifting the whole side, place 1 jackstand each under the corner lifting points, at FULL-EXTENSION... do the drivers side first...  Ditto the passenger side, BUT LEAVE the jack in place and lower it maybe 0.5" so it is a back-up, in case the jackstands fail, but it is NOT bearing any load... (could cause they whole deal to shift.)  Lay down a HEAVY piece of corrugated cardboard... Let's you SLIDE in and out from under the car real nice.
The O2 sensor is screwed in to the CAT, up on top, there are four wires.  FIRST! Go open the hood and locate the O2 connector... it's kinda near the oil dipstick tube, about half-way down. It should be clipped to a metal standard...release it...there is enough slack to lift the whole assembly up higher for a better look.   It is a BLUE plastic connector with a RED slide-Lock passing through it's mid section. Use a small thin screwdriver under the looped bail of the red slide lock and pry it gently to the side, extend it as far as it will go.   Separate the 2 blue plastic halves make sure that the end of the harness that goes down below to the O2 sensor is not wire tied anywhere.
Go back Down Under the car, pull the wire down and cut any cable ties holding it to the dipstick or elswhere.  Now on the left side of the transmission there are 3 plastic snap-lock clips holding the wires to the transmission pan.  Squeeze them from the inside with a thin nosed plier and release all three.  On the UPPER, TRAILING EDGE of the transmission tail bracket, there are 3 10mm headed bolts holding the wire to the bracket. Remove all three.   A small 1/4" drive ratchet is great for this.   Then remove the ONE speed nut holding the wire up on a heatshield in front of the CAT.   Follow the wire... THAR she IS... sticking out of the top of the CAT, in front of the honeycomb.   It is a 22mm facet on the base of the sensor. Get a 22mm socket with the sidewall slotted out for the wire to pass thru (Editor: known as an "oxygen sensor wrench")... if you can... but I just squirted a bit of PB Blaster on the base and let it sit for a few minutes.
I ended up using a 22mm spanner wrench open end to the sensor.. It cracked free quite easily... you may be so lucky..  Then you just un-screw it.  I know this is trite....but...."Re-Assembly IS reverse order". REALLY!  [Note from WBain] Use an anti-seize compound on the threads (if the sensor did not come with any.) It will make any future disassembly easier. [Caution from David Hunter]  Also make sure you are not cross threading it - easy to do on the O2 sensor.

Exhaust Manifold Leak. [Problem:]I own a 1990 740 wagon with the B230F with an exhaust leak at the manifold. Is this a common problem? Do the exhaust manifolds warp easily? [Diagnosis:] The exhaust manifold gaskets on the B230F tend to blow out every once in a while. Mine has a leak next to #1 but since it's not major or real noisy I'm waiting for the rest of it to go or get worse. If you have to change the gasket be prepared to get new bolts/studs and keep a stud extractor handy as they always break off.

Exhaust Manifold Gasket & Studs Replacement. [See the section Turbo: Broken Turbo Exhaust Stud[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.

Applying Penetrants.  [Response 1: 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.

Using Heat.  [Response 2: 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.

In the Event of a Broken Exhaust Manifold Stud.   [Query:]  How do I remove a broken exhaust manifold stud, broken off below the surface.   [Response: Paul Seminara] Got a right angle reversible drill? Got a moto or air grinder tool? Got some diamond bits?  Got a locking collar type stud remover? Got the appropriate size left hand cobalt drill bit? Got the appropriate drill and tap?  With the above tools it's actually not that bad (BTDT).
Start with the left hand drill bit (smaller than the stud in question, correct size for stud remover) with the drill in "R". Maybe the stud will come out maybe not. If not give the stud remover a shot. DO NOT, I REPEAT DO NOT EVEN THINK OF USING AN EASY OUT.
If the stud remover fails or doesn't cut it you must go into full dentist mode with your high speed tool and diamond bits. Just follow the stud and don't go outside the envelope. When most is gone simply drill the hole to the correct size for the tap. Clean hole. Tap, clean and insert stud. Done.
[Cautionary Note] I have fixed broken head studs three times before, on different cars.  On all of them I pulled the head and used a drill press and "easy-out" to remove the stud, also lots of heat.  You can buy an easy-out/drillbit set at most autparts and machinist places.  The drill press ensures an accurate hole (remember, the head is softer than the bolt; you don't want to miss!)  It was pretty easy.

Removing a Broken Stud with a Right-Angle Drill.  [Tip: Bob Mohr] Been there, done that.  A right angle drill will work just fine. I'd suggest using a diamond bit in a Dremel rotary tool to put a nice, centered starting "dimple" in the middle of the broken stud to prevent the bit from walking once you start. You shouldn't have to buy a special diamond tipped drill bit. I went down to the local industrial supply and purchased a cobalt bit that went through that old stud like a hot knife through butter. Have a bottle of cutting oil nearby and squirt a little in the hole every quarter inch or so to cool the bit and flush out the shavings. I ended up drilling it out oversized and installed a helicoil. It worked great.
   Another tip if you don't have a right angled drill. I used one of those fiberglass reinforced cutoff wheels in a dremel to reduce the length of my cobalt drill bit. You have to be careful chucking the drill bit, as it's tough to get it in straight. Cutting down the drill bit gives you just enough clearance to get a straight shot at most of the studs with a plain jane 1/4" drill.
  DANGER, DANGER, DANGER! Do not attempt to drill a hole in the stud and use an extractor/easy out. The extractor can and probably will break off in the hole. Then, your available options are reduced to pulling the engine and having a machine shop mill out the extractor/old stud or spending 24 hours and a dozen diamond bits to hog out the broken extractor millimeter by millimeter. It ain't fun! Both Seminara and I both went through this torture!   [Tip 2: Dick Riess] Have done it with the 90 degree drill, unfortunately w/o diamond bits and kinda made a mess, but my machine shop friend let me use his Time Cert outfit to fix it. Evidently the Time Cert is used extensively on hopping up the old aluminum VW engines. They just don't come out. So if you mess up the threads, there is still hope.  BTW, I am going to have to get some of those diamond bits from Paul---they sound like a life saver and you can count on needing them eventually.

Replace All with Stainless.  [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?

Turbo Notes.  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.

Painting the Manifold. [Tip from Tom Irwin]  Don't paint your exhaust manifolds, even with hi-temp paint, no matter HOW COOL it looks! The paint burns off under the bolt heads and relieves bolt compression. Almost ALL were under torque spec. [Editor] Probably OK to paint IF you don't paint under the bolt heads.

Catalytic Converter Diagnosis.  [Tip from Fluke Corporation:] Using a Fluke Digital Multimeter with the 80T-IR/E Extended Range Temperature Probe, you can easily and quickly assess catalytic converter efficiency. For this test, first run the engine until the engine is warm and stabilized. (For engines with electric cooling fans, let them cycle a few times prior to the test) Then shut off the engine and disconnect a spark plug wire on one bank of cylinders. (Note for V engines: If there are dual converters, you will need to perform this procedure on each bank of cylinders.
Restart the engine and block the throttle to maintain 1000 RPM with the one cylinder not firing. Measure the inlet temperature of the converter and compare it to the outlet temperature. You should see a differential of 50 degrees F. or more if the converter is working properly. If the temperatures are less than 50 degrees apart, then the converter needs to be replaced. Before replacing a converter, be sure to determine why it may have failed. If it is a very high mileage vehicle, it is probably just expired. If it is low mileage, you should perform a thorough check of the vehicle to determine the cause.   For normal engines with a misfiring cylinder at 1000 RPM, you can expect that the temperatures observed will be in the 600 to 900 degrees F. range.

Replacement Converters. The cat thread was my doing since I raised the question regarding my '85 740 GLE. To sum up all of the advice I received, replacing the cat should be done if it is indeed in faltering condition--although people seemed to vary in their senses of urgency for having the replacement done. The reason for having it replaced--besides making passing emissions dicey in some states--is that the cone in the converter can come loose and plug the exhaust or can break up into pieces and shoot back through the exhaust into the muffler, etc.

I also called around about aftermarket cats and found one for $100. Herzog-Meier 800-858-6608 sold the VCNA aftermarket for $305 since I'm a IPD customer (you have to tell them this to get the 20% discount!) If you can replace it yourself maybe that would be a good idea (I can forward you the email I received from the car parts place). If you can't then I suggest taking it to Midas or somewhere that specializes in that stuff and replaces them on a regular basis. My Volvo guy was quoting prices of up to $350 installed. Based on some advice from a list member, however, I went to Midas two days ago and had it done in an hour for $208 not including tax.

[Another Query:] The catalytic converter on my 1989 740GL Wagon needs to be replaced. One shop said that they do not recommend after-market parts, since the performance is never as good as with the manufacturer's parts. Another shop didn't see any problems with using an after-market catalytic converter for about $350, compared to manufacturer's (Volvo's) price of $1300. To me this is a large difference. I am wondering if anyone else has any experience with replacing the catalytic converter  [Response: Zee] Euclid Foreign Auto Parts, near Cleveland, OH can sell/ship a decent aftermarket cat. for about $150 (Euclid"s tool-free number: 1-800-837-5110.  You must ask for Tina and mention the Brickboard bulletin board for the discount.)  I have had a good buying experience with them over Christmas when I ordered a Bosal downpipe (it's the one just in front of the cat. that goes between the cat. and the exhaust manifold). $69 +$10 tax and shipping, sent to my door within two days from Rochester, NY. (I live in PA)  What you want to look for when buying any after-market part is that the part meets or exceeds O.E.M. specifications (Original Equipment Manufacturer). You have to ask, or tell parts suppliers you want this, or they can sell you cheap, Asian look-alikes.

Exhaust Replacement: Brands [Editor: Numerous questions about which brands to buy are addressed below.]
[Response 1:]  I replaced the exhaust system on my '87 740 Turbo last summer with a Volvo kit. The kit which includes all the hangers and clamps for the car was about $285 and only took me about an hour to install. The kit includes everything from behind the cat.
[Response 2:]  I bought the Volvo kit because I have heard that they last longer than the muffler shop kits. Having had a few 240s over the years, I have visited the muffler shops a lot. However, the 240s have so much exhaust plumbing compared to a 740, I would expect the 240 to go through them faster. I figured that at $285, it would cost me about that much to have a muffler shop do the work. Then I will have to deal with the periodic returns to have the system replace under warrantee. Figured it was worth a try.
[Response 3:]   I bought a replacement system mfg. by Starla, just received yesterday. All parts made in Sweden. EVERYTHING from the rear of the cat back, including clamps and hangers, was $245 including shipping. Bought from RPR.
[Response: Vladimir Kordac] Stay with Volvo or a quality after-market system. Forget Walker, Maremont etc. with their 2yr "lifetime" crap unless you want to eek out a few more years out of the present system!  I put in a complete Bosal system recently from down pipe to tail pipe including cat, that went in flawlessly. Total cost was approx. $325. Bosal is supposedly comparable to OEM. We'll see.
[Response: Rob Bareiss] Either the IPD system or the factory Volvo exhaust kit will make you happy. You will also find parts stores which stock "Starla" brand original fit exhaust components. The stuff is great quality.  Goes on just like Volvo's. Lasts as long as your originals did, and costs about the same (a bit less). We use a lot of Starla and Volvo brand parts at our shop, and the difference between those, and the "M" or "W" brand junk we throw away is amazing.  Get the real stuff, you'll be much happier you spent your money WELL and ONLY ONCE.

Exhaust Replacement: Procedures.  To remove the front muffler pipe from the cat. pipe, I put a reinforced cut off wheel on my Dremel tool and slit the muffler pipe just deep enough so as not to cut the cat. pipe. Pried open the slit on the muffler pipe and everything came apart. (Also need to slit the joint behind the front muffler so that it can be separated from the over-the-axle pipe, but here you don't have to be so careful with how deep you cut.)
Installing the Volvo kit was a dream. All the parts FIT! None of the pipe ends were dented requiring hammering to make them go together. The pipes had smooth curves, not ribbed curves as often found on after market kits. Furthermore, the system is probably better sized for the car which hopefully will result in less trouble for us turbo owners.
[Response:  Gary DeFrancesco]  These hack muffler shops are more trouble than they are worth. I have not had the pleasure of getting into the exhaust system of a '89 740, so I don't know what the differences are with the earlier 740s. Assuming the basic design and arrangement is the same, and speaking from experience with my '87 and '88 740Ts, I would go with the Volvo exhaust system. The kit Volvo sells has everything you need behind the cat. It even includes the hangers. My dealer hit me just less than $300 for the kit, and it went in like a dream. It took me less than an hour to do the job.
In your case, you have to deal with the muffler pipe being welded to the cat. One approach  would be to cut the muffler pipe off several inches down stream from the weld. Then using a die grinder, remove the remains of the muffler pipe from the cat pipe. A Drummel tool will also work, but it will take longer. The first thing to do is slit the muffler pipe open length wise. Then carefully slit the muffler pipe next to the weld to free it from the cat pipe. The idea is to not cut into the cat pipe while doing this. It will take a gentle touch and some time. Once the muffler pipe is off, then the weld can be removed with a grinder wheel. However, if the weld is far enough onto the cat pipe, you may have little or no need to remove the weld bead if the new muffler pipe does not go on the cat pipe as far. This will be a PITA job. But the cost of a new Volvo cat may convince you to get creative. (Don't know what a cat for you car cost, but Volvo wanted over $850 for my '88 740T!)
This leads to another approach to the job. Replace the cat with a good quality after market unit. There are some decent ones out there for reasonable cost. Just make sure it is a direct fit unit and the pipe diameters are not restrictive entering or exiting the cat chamber. With a new cat and the Volvo exhaust kit, you should be able to replace the exhaust system in an hour or two.
[Response: Vladimir Kordac]   You'll have a small problem with that welded cat. May have to cut back beyond the weld and use a small adapter piece to mate cat and front muffler (resonator). What kind of shape is the rest of the exhaust?  Unlike hunting an electrical problem that may take me hours-years, changing an exhaust is a no-brainer. And results are dramatic. Usually the worst part is getting the old stuff off; however, since I was replacing everything, I didn't have to mess with cat connections or any
other frozen areas. In the past I would get out the Dremel or rotary cutoff tool to slice through clamps and pipe ends. It would help a great deal to elevate car on all fours.
[Response: Warren Bain] On installation, don't forget the Permatex anti-seize compound on the threads,  it makes removal a dream. I use it on all my exhaust systems and the bolts just turn right off with out any problems.

Exhaust Brackets Keep Breaking.  [Query:] 've replaced the exhaust bracket about three times during the past 5 months every since I replaced the system.  The bracket keeps on breaking/splitting at the same exact point all the time.  Does anyone know why this is constantly occurring?  [Response: Paul Grimshaw] Check your motor mounts.  Bad mounts can put greater torsional strain on the pipes. If they're sagging or twisted, replace both of them.  Also suggest changing the tranny mount at the same time.  Next, loosen all of the pipe joints, replace your bracket.  Now lightly wiggle the pipes to find their (untensioned) resting point.  Make sure that no areas of the pipe are touching the chassis.  Make sure that at full droop, your 740's rear axle is not hitting the cross-over pipe.   Now tighten things up carefully.  [Response 2: Dana] Make sure you still have the spacing ring in between the two pipes and that all the exhaust flanges are in place and not stretched out to far.  I had a problem with my bracket and clamps loosening up every 1000 miles or so.  Turned out the bracket was a manufacturing defect and the clamps I used couldn't hack it.

Exhaust Smell: Leaking Injector Seals?  [Query:] I have a problem with my 760 Turbo that my mechanic can't solve: when accelerating hard, with the ac and the fan on, a strong smell of exhaust comes out of the vents. when the fan and the ac are off, there is no smell. Can anybody help with this? The mechanic says that it can not explain why there should be any smell of exhaust coming in, which, by the way, happens also with the recirculation button turned on.  [Response: Steve Seekins] I suspect that what you smell is not exhaust, but raw gas. I had this problem on a couple of turbo cars.  The source was injector seals. When they get bad on a turbo, they suck air into the manifold at idle and off throttle (whenever the turbo gage is in the vacuum zone). However, under boost, the manifold is pressurized and fuel mist from the injectors is forced out past the injector seals and then gets sucked into the vent system by the intake at the front of the windshield. It is worst under heavy load when manifold pressure is highest and more fuel is being injected, and you only get it when the vent system is operating or the windows are open.
Check at idle with can of spray carb cleaner or unlit propane torch jet. Spray or direct jet at each injector base in turn. Any change in engine rpm indicates leaking seal. Also check intake manifold gasket area and look for combination of bad hose from fuel pressure regulator and leaking pressure regulator.

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