Hi Brickboard readers

Learned a lot from reading this board and I have a question regarding my sister's car. a classic 1991 740GL.

we were driving over a moderate incline today and my sister gave the car a little more throttle as she usually does when she felt a loss of power[ we were slowing down half way up and other people were passing us]. I did not feel the car surging forward. as a matter of fact, we were still slowing down. suddenly, we saw a large cloud of blackish gray smoke emitting from must have been our car's tailpipe through the rear and side mirrors.

both of us panicked and my sister gun the throttle again to make sure and sure enough it did it again. just a large cloud of blackish gray smoke.

the smoke went away as she eased up on the gas pedal. we just limped over the incline thereafter. when we got to the top the car ran just fine on the flat and decline part of the road.

is this a sign of trouble ahead for this car?

would a compression test tells us anything?

thanks
I asked my sister to


felt a

Almost certainly you have a rich mixture, due to a failing fuel pressure regulator, an intake vacuum leak, or a sensor problem. Start with the intake system and look for hose splits, leaking gaskets, etc. per the FAQ instructions.

I agree with Steve, here are my best guesses at your problem:

1. Fuel Pressure Regulator has a burst or tearing diaphram. Replacement cost is about $40-$50 and they can be ordered from FCP Groton. Typical life expectancy is 150,000 miles, and they can be checked with a standard vacuum pump and seeing if it holds 20"HG on the gauge for a minute or so.

2. Air Mass Meter Failure (if you have LH-2.4 Fuel Injection). The Air Mass Meter (Bosch 016) is having problems correctly measuring the amount of air entering the engine and thus the Fuel Injection Computer can not match the proper amount of fuel with it (overshooting and causing a rich mixture).

3. Fuel Injection Computer Failure (if you have LH-2.4 Fuel Injection). I have a pile of dead 561 ECUs (computers) and have even seen two of the later/improved 951 computers fail.

4. Vacuum leak in tube between intake manifold and MAP sensor or failing intake temperature sensor (Bendix-Rex/Regina Fuel Injection System only).

5. Clogged Air Filter. If the air filter is clogged, and you put your foot to the floor, the Wide-Open-Throttle Switch would be tripped and the computer would put the maximum amount of fuel into the engine that's permitted in it's programming. If the Air Filter is clogged, this would restrict the flow of air and cause the mixture to be very rich and you would be loosing horsepower rather than gaining it.

God bless,
Fitz Fitzgerald.

Yes, the compression test will tell you something. Sometimes it is that compression is OK, which rules out a lot of possibilities.

Black/gray smoke is often the result of a too-rich mixture. Not all the fuel is being burned. Why? Lots of possibilities there, too.

When you do the compression test, check each plug. Mark each with its cylinder.
Inspect for color, wetness, burning, etc.

Put in new plugs. Maybe ignition wires and a dizzy rotor, too.

After the episode, how did the engine run? Same as before or what?

Good Luck,

Bob

:>)

How low was the gas in the tank? There could be a fuel pickup problem if this only happens when the tanks getting empty. Try it again with a full tank. Going up a hill puts more strain on the engine that may cause piston ring blowby if the rings are worn. Not usually a Volvo problem unless the engine has not been maintained properly with regular oil changes. What's your mileage? A compression test may show you something. All the readings should be within 10% or so.

How low was the gas in the tank? There could be a fuel pickup problem if this only happens when the tanks getting empty. Try it again with a full tank. Going up a hill puts more strain on the engine that may cause piston ring blowby if the rings are worn. Not usually a Volvo problem unless the engine has not been maintained properly with regular oil changes. What's your mileage? A compression test may show you something. All the readings should be within 10% or so.