Engine: Fuel Injection                                                                                        FAQ Home

  Volvo Maintenance FAQ for 7xx/9xx/90 Cars                                                                                                                     Version 5.0
Throttle Body and Throttle Position Switch Adjustment

Injector Cleaning

Injector Seals

Injector Diagnosis

Radio Suppression Relay

Oxygen Sensor Diagnosis

Testing or Repairing Bad Fuel Injection Relay

Fuel Pump and FI Relay Diagnostic Tests

Technical Notes on AMM Calibration

Air Box Thermostat Change

Exhaust Smell: Leaking Injector Seals?

Homemade Fuel Injector Cleaner

Engine Storage/Used Engine Notes

Throttle Body and Throttle Position Switch Adjustment. [Adapted from Volvo Service Manual 32043/1]

1. Checking the Throttle Body (Plate and TPS) Adjustment

Connect an accurate tachometer then warm up the engine.  Let it idle in Park with a/c off.  Pinch off the hose between the air intake and the IAC valve (donít damage the hose with something sharp!)  Idle speed should drop below 500 rpm, or the engine may stop: both are normal.  If idle speed does not drop, adjust as below.  First remove the hose clip.

2. Adjusting the Idle Speed

On the side of your throttle body, there is an adjustment screw.  Loosen the lock nut.  Start the engine and turn the adjustment screw until idle is 480-520 rpm.  Switch off the engine and tighten the lock nut while holding the adjustment screw so it doesn't turn.

3. Checking the TPS Adjustment.

Check the gap between the adjustment screw and the throttle lever with a feeler gauge.  Insert a .45mm feeler gauge.  There should be no click from the TPS when the throttle is closed. Then insert a .15mm feeler gauge.  There should be a click from the TPS when the throttle is closed.  If these are incorrect, then adjust as below.

4. Adjusting the TPS.

Loosen the TPS adjustment screws.  First turn the TPS clockwise (away from the electrical connector) until it stops.  While keeping your finger on the throttle disk so it won't move,  turn the TPS counter-clockwise (toward the connector) until you hear or feel a "click".   Continue turning until it stops, then tighten the screws.  Go back to step 3 above to check the adjustment.

Injector Cleaning. [Editor's Tip: see Michael Ponte's excellent illustrated discussion of injector cleaning at http://www.mikeponte.com/volvo/injectors.htm]
[Query: What is the best injector cleaner?] I've tried a few kinds but I found that removal and flushing of the injectors and replacement of the injector seals really is the best. I removed the injectors in my 85 245 Turbo (K-jet) and took them to a shop and they pressure tested and flushed them. Even with all the injector cleaner I ran through (some of it was pretty expensive), they were still really crudded up. After the flush they were like new. The flush and test cost $13.00, the seals (for my brick there was a thin one on the injector holder, and a fat doughnut one on the injector itself - not sure what your brick has) were $3.00 (?). Total cost is much less than bottles of injector cleaner that are (in my case) of limited help. I guess in really bad cases a new injector may be required, but not with my brick. Injector removal and installing was pretty straightforward - and I'm not all that handy with tools

[Response 2:] I used expensive injector cleaner with marginal success - so I did an injector overhaul. There are some shops that do a "complete flush" without removing the injectors using some technique, but I decided to do it myself. Removing injectors was straightforward - just keep things clean. I took the injectors to a shop and they did a pressure flush ($15). There are other home ways to do this like using bicycle pump with pure injector cleaner - but after a few attempts I decided not to try. They were badly crudded but after a bit of flushing, were good as new. After 220 K km, the shop said they were just fine. I also replaced the 2 rubber o-rings. One around the injector (fat doughnut type) and one around the injector holder (skinny ring type). The o-ring around the injector holder was brittle - so the new rings sealed a big vacuum leak. Use silicon lubricant to ease the o-ring replacement. All this took a couple of hours. Made a big difference at idle.

[Tip from Ed O'Briant] My experience with a rough idle still present after a tune up and TB, IAC cleaning, etc., on higher mileage cars has been this (assuming no vacuum leaks, etc.):  dirty, clogged, sticky, leaky, and otherwise compromised fuel injector operation. If you haven't done it, pull the fuel rail and the injectors. Either bench clean them yourself or send them off to the proper folks.  Chemicals in the fuel tank don't cut it! They may help somewhat but in no way replace pulling those bad boys!  On our '90 745T with 115K miles, I found that all four of the injectors had LOUSY spray patterns-streaming fuel instead of atomizing it. Also, two of the injectors were leaking-when power alone was applied to the leakers, without compressed air, the injectors just dripped cleaner when they should, of course, be tight. Leaking injectors cause a very lumpy idle! Hard, brittle, cracked injector o-rings are also antithetical to smooth engine operation.
After cleaning, none of the injectors leaked and they atomized the cleaner so well that the vapor hung in the air for a minute or more. Idle is now incredibly smooth. Smoother and faster acceleration/deceleration, no hesitation, as well. A testament to this is my wife's attempting to start the car TWICE since the injector cleaning, which is not normally a problem, except the car was already running!
Remember this if nothing else: There is NO such a thing as a clean, optimally performing fuel injector on a high(er) mileage engine, despite whatever the injector manufacturers/oil refinery folks may say about modern injectors and fuel blends, making injectors all but impervious to getting crudded up. It just ain't true.

Injector Seals.  [Tip from Tim Curry] These seals are very simple to install. Disconnect the battery, this will shut off the fuel system completely and reduce chances of an impromptu BBQ under the hood. Disconnect the fuel line and allow any gas to drain into a container. Mop up spills and put towels away from the car.

The fuel rail is the thing that holds the injectors in place and provides fuel pressure, unbolt it. The metal rings which go from the injector body to the fuel rail just act as snap rings. They are pushed on from the side and lock the fuel rail to the injector. Most likely, the rail will have to be separated from the injectors before you try removing them. They just push into place with finger pressure (into the rail and manifold), but can become stuck with age, grunge and dried rubber. Carefully, wiggle pry or pull the injector out of its hole in the intake manifold (one at a time please).

Use the seals in the kit (Bosch injector kit, import parts house, o-rings) with a small dab of grease, vaseline or lubriplate and install them where the old ones were. There is a plastic cap that protects the injector's tip which can be replaced as well. The old one will be stuck so you may need to gently break it loose with a pair of vise grips, adjusted to just barely crush the cap slightly. Make sure to use a dab of vaseline on the end of the injector before putting the plastic cap back on, or it may split. I used a block of soft wood (pine scrap) with a hole drilled in it so the injector needle wouldn't be damaged when
pushing the tip back on. Don't bugger the end and needle, or you will be buying a new injector ($$$).

Put the injector back in its hole (again, small dab of grease) and go to the next one. Do all of them or you will cause leaks. Put the rail back in place, set the clips, tighten bolts, attach fuel line. Make sure no parts are left over. Check everything again for tightness. Attach battery. Start car. Check for leaks.

Be careful, take your time. Its not hard to do, just think and keep parts in a container as you go.

Injector Diagnosis. To verify operation of the injectors, measure the spray pattern and throughput of each using a graduated plastic beaker. Should one or more injectors be inoperative, and if your engine has considerable mileage, replace all injectors & fuel filters (including the small catch screen in the main fuel pump). Those on a budget may try to clear the injectors using concentrated cleaner, but this method has hit-and-miss results, especially if there is a foreign object clogging the injector. Don't expect a disconnected injector on # 2 or # 3 cylinder to result in a change in engine note (at idle). Your Volvo's engine uses "port fuel injection" with some cross-over occurring within the plenum. The injection pulses can vary considerably, and Volvo FI set-ups fire the injector twice per revolution (keeps the valve wet between intake cycles) to prevent hardened deposits from forming on the valves. This often results in enough fuel being present for near-normal engine operation on three injectors. That being said, use a volt meter to measure the voltage being supplied to the injectors. Lacking a volt meter, one may ensure injector opening/closing by placing a screwdriver against the base of each injector when the engine is running. Placing an ear close to the handle of the screwdriver should allow a faint "clicking" to be heard. This is the injector solenoid opening and closing. To obtain a better appreciation on combustion conditions within each cylinder, one may pull the plugs for observation. Dark grey/brown indicates normal "burn". Light grey/white indicates lean "burn". Black and oily usually means a rich "burn" or oil control problem.

Radio Suppression Relay. [What is the Radio Suppression Relay and where is it?] The radio suppression relay (as it's called) is in actually a fuel injector relay. The pre 1986 injectors were supplied constant + power to one terminal and supplied a timed ground to the other terminal via the ECM. The constant + power used to come from the fuel pump/injection system relay. In 1986 Volvo decided to isolate the fuel injector circuit because of some radio interference created by the pulsing circuit. The solution was to energize a relay (the radio suppression relay) with the pump/system relay feed instead of using it to power the injectors directly. The radio suppression relay then supplies the + power to the injectors. The timed ground still comes from the ECM. The reason Alex can't find his radio suppression relay is because it's located on the other side of the engine compartment behind the power steering reservoir, (relay closest to the engine of the two relays mounted there Alex). For the most part the non-turbo engines had the radio suppression relay mounted on the right side (pass) of the engine compartment on or near the coolant reservoir as Alex mentioned. The turbo engines had the radio suppression relay mounted on the left side (drivers) of the engine compartment on or near the shock tower. Not set in stone just as a general rule. The radio suppression relay was used from 1986 until 1995 on almost all LH injected 4 cyl and V6 engines. There may be a couple of exceptions. The 5cyl and straight 6cyl engines do not use one. When it's bad or missing, the radio will work fine, but the engine will not run. Remember even though it's called a radio suppression relay it's function is to supply + power to the fuel injectors.
Problem diagnosis:  If you suspect that your radio suppression relay is faulty (causing hot start problems, etc.) try switching the leads with the electric cooling fan relay if your car is so equipped.  This relay is identical and in many car lines is located right next to the radio suppression FI relay.  If your fan stops and your engine starts, then you've isolated the problem. See also Hot Start Problems.

Oxygen Sensor Diagnosis. [Question: How do I diagnose oxygen sensor problems?] This is from Bosch information:

Test for a rich mixture as follows:

Test for a lean mixture as follows: Test dynamic performance as follows:

Homemade Fuel Injector Cleaner. An article in performance engineering recommends 1,1,1 trichloroethane and a stiff bristle brush to clean the outside. Don't immerse the injector, just scrub at it. An ultrasonic pen or jewelry cleaner and fuel injector cleaner (Chevron Techron) to clean the outlet. Stand the injector up in the cleaner so the outlet is in the solution and run the cleaner to 10 minutes. Run a half n half mixture of mineral spirits and injector cleaner thru the injector on the bench to clean the inside. [Another:] He showed me a very interesting way to clean the injectors while in the car. We took an air compressor line water filter with the filter removed, and filled it with straight fuel injector cleaner (like what you would buy at K-mart). We then tripped the inertia switch on the fuel pump to shut off fuel flow and connected one end of the 'water filter' to the schraeder valve on the fuel rail. The other end of the 'water filter' was connected to a simple air compressor regulator which we regulated to around 35 psi and then turned on the air. We started the car and ran the straight fuel injector cleaner through the injectors. Apparently, this is in essence the same way garages and dealerships use to clean the injectors while on the car (using perhaps slightly less kludged equipment). Although it doesn't account for backflushing or screen replacement, it did make an excellent difference in the idling and off-idle performance of my car. Not so much in power but in smoothness. All done with probably $15 worth of hardware (providing you already have an air compressor).

[Another:] A two line flush system is a must. I was selling and training the CarbonClean unit way before Motorvac hit the street. The Motorvac is a spin off the carbon clean . Any unit that uses the two line flush method is worth having done. The GM top engine cleaner and the Ford factory stuff is great chemical and should be used at a 5 to one mixture rate with the gasoline. We have done tons of reasearch on the chemicals and these passed with flying colors. Keep watching our web site for my article " fuel service of the 90's" will post at : http://www.lindertech.com/

Testing or Repairing Bad Fuel Injection Relay. I had a similar no-restart problem on my '89 780, and the problem was, in fact, the fuel injection relay. Try this. If the car quits and won't restart, try banging your fist on the left side of console, at about ash tray height while cranking the engine. If it starts, the relay is probably flaky. It sounds weird, but that's how I found my problem. If you want to be more sophisticated, use a volt meter to check the voltage to ground at the injection ballast resistors. You should see 12 volts when you turn the key on. If not, thump the console. If the voltage comes on, it's the fuel injection (pump) relay.   [Response 2:] The Bosch relays can be resoldered very easily by anyone handy with a soldering iron and soldering gun. And a little experience. Remove the plastic relay cover and examine the foil side of the printed circuit board (on the flip side from the electronic components). With a magnifying glass you'll probably see the solder cracked, crystallized, and overheated around the heavy connections to the actual relay -- they look like little "buttons" coming through the silvery solder.  I use a soldering gun the heat & resolder these heavy connections, and a small 25 Watt iron for the other connections. Be very careful not to form a "solder bridge" between adjacent foil traces. You might consider drilling several holes in the plastic case for ventilation -- a good idea.
[Tips from John O] What I've seen occur with some of those relays isn't cracks but sticking contacts, like any electrical contacts do with time and use. That's why I just replace the relay. Otherwise, try soldering it and filing the contacts if possible but for $50, I don't think it's worth the gamble in my humble opinion. Also look at the terminal at the relay box for discoloration as they sometimes get so hot that they melt the plastic.

Fuel Pump and FI Relay Diagnostic Tests.  Here is a procedure to test the operation of the fuel injection relay and the operation of both fuel pumps.  The 3 main things to check in the fuel circuit are the fuel pump relay, and the 2 fuel pumps. CAVEAT: The main fuel pump is not designed to be run without the in-tank pump "on", so get the second part of this test over quickly.  You should not need to keep it running in this condition for more than a few seconds to complete this part anyway.

Technical Notes on AMM Calibration. This is a response from Python Injection (rebuilders of AMMs) to a question I had about testing AMMs.
From:  Joe Evert,  Director of Engineering,  Python Injection
Subject: Re: Technical Question about AMM
The reason the OEM doesn't give a test procedure for the air mass is two  fold.   First of all BOSCH Hot Wire Air Mass sensors are not linear devices like a throttle position sensor. The output does not change the same amount for a given air change. To make it short, most linear sensors will give you say... 1 volt for 100cfm air flow, 2 volts for 200cfm air flow, 3 volts for 300cfm airflow etc. This is a linear device. For every 100cfm of air flow the output changes 1 volt. This is just an example of a linear device. Bosch hot wire sensors are not like this. They change a great deal at low air flows but once the air flow increases past a certain point, say 50% of what the engine can draw, they change very little. This makes the sensor very accurate at low to moderate air flows and good enough at high air flows. Just a small amount
of inaccuracy at low RPM and the vehicle will run terrible. If the voltage for a given air flow is off by 100 milli volts at low RPM the car will barely run.   At high RPM A 100 milli volt deviation will not even be noticed. Because of this it makes it next to impossible for the technician to accurately diagnose the air mass in the field. We use a calibrated flow bench that measures the exact CFM air flow to then compare the voltage to. This is not pratical in the field because temperature, altitude, humidity and the mechanical condition of the engine will will affect how much air the engine is drawing in. So just to say that the Air mass should have xx.xx volts at idle would be completely false since all these parameters must be accounted for. Also even if a range is given just a small amount of deviation in the output causes poor
performance. So what are you to do?   Well we calibrate our sensors on our flow bench so that every one of them is perfectly calibrated. For on vehicle diagnosis the best way to diagnose it is just unplug it at idle, if the vehicle runs better it is most likely bad.
This is because if the air flow sensor is off voltage at high RPM it will also be off at idle. Also if you are experiencing repeated failures you probably have a defective air box thermostat. This little thermostatic bulb is located in the air filter box and controls the hot air into the engine. When this fails it fails in hot air mode and routes hot air from around the manifold into the air intake. This will destroy the air mass meter in no time.

Air Box Thermostat Change.  [Query:]  Can I change the air box thermostat in 7xx/9xx cars with an integral lower air box/thermostat combination?  [Response: Steve Seekins] You can change just the thermostat element on any of the cars that are equipped with it. Only need to change the flapper if the hinges are worn or broken, or if the gaskets are destroyed. It will require a bit of fiddling to compress the spring to get thermostat element out/in - helps to have 4 hands - it is difficult to compress the spring with one hand.

Engine Storage/Used Engine Notes.  [Tip from Linder Injector Services]  If you have installed a salvage yard engine, depending on how long it has sat it may have clogged injectors or fuel rail.  The ones that I have seen require the injectors to be serviced off the engine.  This will ensure that the inlet filters are clean (new) and their flow is correct with the  appropriate spray pattern.  The rail was flushed or ultrasonically cleaned.  The pressure regulator had to be replaced on a couple of systems due to a lot of sediment.  Most of the time this was a simple process that was fairly inexpensive.

Volvo Maintenance FAQ for 7xx/9xx/90 Cars                                                                                                                     Top of Page