Maintenance FAQ for 7xx/9xx/90 Cars
Body and Throttle Position Switch Adjustment. [Adapted from Volvo Service
1. Checking the Throttle Body (Plate and
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.
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.
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
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.
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.
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
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:
Disconnect the sensor lead to the control
Run the engine at 2500 rpm
Artificially enrich the fuel mixture on
electronic fuel injected engines by removing and plugging the vacuum line
to the fuel pressure regulator.
If the voltmeter rapidly reads .9 volts,
then the oxygen sensor is correctly sensing a rich mixture. But, if the
voltmeter responds sluggishly, or if it stays below .9 volts, try running
it at 3,000 rpm for a few minutes, then check again. No improvement means
you buy a new sensor.
Test dynamic performance as follows:
Induce a small vacuum leak
If the voltmeter rapidly drops to .2 volts
or below in less than a second, then the oxygen sensor is correctly measuring
the lean mixture. But if the voltmeter responds sluggishly, of if it stays
above .2 volts, give it the 3,000 rpm treatment and try again. If
no improvement, then the sensor should be replaced.
Reconnect the sensor lead and tap your
meter into the signal wire
Set the mixture to specification.
Run the engine at 1500 rpm.
You should see rapidly changing readings
that average somewhere around .5 volt as the computer keeps adjusting the
blend. The sensor output should fluctuate around .5 volts. If it
doesn't, replace the sensor. Deciding whether or not response is
slow enough to justify replacement requires some judgment. A common rule
of thumb for minimum activity is eight trips across the rich/lean line
in ten seconds, and sometimes you can find specs for cross-counts.
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/
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.
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.
1. Fuel Injection Relay Test.
There are 2 relays inside the fuel injection/pump relay. One of them should
turn ON when the ignition is turned on (without turning over the engine),
and the other relay (which actually turns the fuel pumps) should come ON
when the engine turns over/runs. You can check the 1st relay by putting
your fingers on the relay module and turning the ignition on and off repeatedly.
You should feel the relay click on every time. If it doesn't, that relay
isn't working. And you'll find the car doesn't start if the relay did not
[Tip:] To check for possible fuel pump
relay failure go between center of cig lighter plug and fuse 11, should
be less than .5 V (<500mV). Excessive resistance creates voltage drops
that will exceed these values. The volt drops will be high due to poor
contact points in relays or the solder joint problems. It is best
to check these volt drops after it has run for a while as that is when
the failures usually occur.
2. Fuel Pump Diagnostic Tests.
On the 740, the fuse-box + relay box can be pulled out a little to facilitate
inserting/removing relay modules. So pull it out as much as the wires will
allow. Pull out the fuel injection/pump relay module. Now take a small
piece of wire to jumper terminals 30 and 87/2 on the relay board (the terminals
are identified on the relay module pins. The 2 terminals are the nearest
left and middle right pins on the relay board). This should make the car
act like the fuel pump relay is ON.
Now turn the ignition ON (without turning
the engine). You should hear a whirring sound right from where you are.
That will be the main fuel pump. Now go to the gas tank and unscrew the
cap. Put you ear to the hole and you should hear a smaller whirring sound.
That will be the in-tank pump. If you hear both noises, the fuel pumps
should be OK.
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.
To check the pumps individually, you can
pull out the in-tank fuel pump fuse after you do the above test, and repeat
the test. You should not hear any whirring at the tank, but you should
be able to hear the main pump.
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
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
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
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.
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.
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.
FAQ for 7xx/9xx/90 Cars
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