1990 740gl 200k miles. Sitting in drivethru, then engine starts running ruff like it wants to stall but doesnt. Exhaust fumes become really bad, smells rich and comes in cabin of car. Car does run and will get up to speed but engine vibrates at idle. Engine seams to smooth out at 3000 rpm. Once u shut car off it will restart only if u press gas pedal half way and leave it there as u turn key. Its a Rex Regina and timing belt, tensioner were replaced 6 months ago by mechanic. Where should i start?

 

I'm thinking, fuel pressure regulator. It might leaking gas into the vacuum hose. if that is good, then engine coolant temp sensor "the one closest to the oil separator box".

 

Thanks, i got code from computer for the temp sensor after i posted. Ive ordered part from ipd, will let u know how it turns out

 

just fyi there are 2 temp coolant sensors on the cylinder head, both are on the intake manifold side. the one closest to the timing belt is for the temp gauge. The other nearest the oil separater box is for the engine fuel and ignition timing computers.

 

ECT problems are as likely to be corroded/crumbling wiring as the actual ECT sensor.

 

Fratoright, did you have any luck fixing the problem? I have a similar problem. Rough idle, and stalls out. I thought it was the fuel pressure regulator relay. But I am having trouble getting to it. The cubbie box wont come out to get to the regulators under the dash behind the ash tray and fuse box.
It did have a problem with a shorted out fuse box on the radio fuse. Burnt the fuse and fuse box holder around the fuse to the radio. I can wiggle the fuse box while driving and that seems to correct the problem. May be a grounding problem.
When they build these Volvo's, they build them well. But this car being 29 years old is not doing to good recently.

 

to remove that cubbie box between the ashtray and radio, you remove the square plastic bezel thats around the cigar lighter opening, and this exposes a long skinny phillips screw, remove that screw, and the box should come right out (take the ashtray assembly out first, of course).

to remove that bezel, just stick your finger a little ways into the ashtray hole, and wiggle/pull the bezel from the bottom right quadrant, and it should come unsnapped.


p.s.. if wiggling the fuse/relay panel is fixing things, the problem is as likely wiring under the relay panel as it is the relay itself.

 

Thanks Pierce. But I done broke it. Got it out though. No bad wiring except the radio fuse plug in. I thought it might be a bad ground. But I'm not sure which is the ground wire. I tried the big green wire, but then the car would not start. I found a site on the web that claim the yellow/black wire is the ground. Do you know which wire/lead is the ground for the fuel relay?

 

I don't have a wiring diagram for anything older than a 1991 740 (which is virtually a 940) and is LH 2.4 rather than LH 2.2

grounds are almost always brown or black wires (but not all brown or black wires are grounds!!).

on the 91/92 740's, under the fuse panel there's a main brass strip labeled 31/31 in the wiring diagrams which is connected to the ground near the right A pillar (down by the right front door lower hinge). most all the other grounds in the fuse/relay panel come off this 31/31 strip.

the LH 2.4 main fuel relay has no direct connections to ground. it has two relays internally, the main and the fuel pump relay.

both relay switches get power from fuse 1 via a brown wire to relay pin 3 (30). The main relay coil is also connected to this. the other side of the main relay coil goes to pin 4, a red wire to ECU pin 21, which is switched to ground to turn on the main relay.. the output side of the main relay switch goes to pin 1, blue-yellow, and is connected to A) lots of blue-yellow stuff including ECU pin 9, and B) fuel relay pin 6, the fuel pump coil.

the other side of the fuel pump coil goes to relay pin 2 and a yellow-black wire to ECU pin 20, which is switched to ground to turn the fuel pump relay on. the fuel pump relay switched output is pin 5, a pink wire, that goes to fuse 11 and the fuel pumps.

 

Thanks. I will check out the Yellow-black wire from pin 2 on relay, to pin 20 on ECU. The other site said if it is grounded that wire the fuel pump will remain running if an accident occurs.
But I can live with that. The car stalling out on a 65 mph freeway can cause an accident, so having it not stall out is a better option for me.

 

I also have a 1996 Volvo 850 Turbo that over heated and the engine froze up on me, that I would like to sell. Or part out and sell the parts. Is there a place on this forum to do that?

 

probably 'for sale/trade', For Sale / Trade - Volvo Forums - Volvo Enthusiasts Forum ... but good luck with that. 850's are a dime a dozen as they frequently need $$$$$ repairs that far exceed the value of the car. if the rest of the car is really nice (perfect interior and exterior, tight suspension and transmission, low overall mileage), your best bet would be to score a junkyard engine and transplant it then sell the whole car.

parting out a car can take years, and then you're left with a chassis to dispose of. few of the parts are worth the labor to remove and ship.

 

I have been very busy with work but have started work on 740. Ive cleaned idle air control valve, replaced coolant temp sensor and replaced fuel pressure regulator. Nothing has worked. Car still starts and runs rough but is running really rich with white/gray smoke comming out of exhaust

 

Hey Pierce, been busy but still no fix for my 740. How would a electrical novice start trouble shooting wiring?

 

Leave the wiring alone for now!
Make sure you have no air leaks between the MAP and the throttle body. (too much air will bring too much fuel=run rich).
Make sure you have no head gasket or burned valve issues: take a compression test to make sure. Report the results. Stop throwing parts at the thing.

 

yeah, white smoke is usually steam, an indication of coolant getting into the combustion chambers.

 

To update you all. I grounded to yellow and black wire lead from the fuel relay number 2 post. That stopped the stall outs. I gained about 2 to 3 mpg. But I still have a vacuum leak. A stutter at acceleration while the engine is cold. After it worms up, the stutter stops.

 

Some more info.. I can feel and hear the idle air control valve vibrating when the car is running, this is after i cleaned the inside. Is it supposed to? There is no sign of coolant in the oil but there is alot of fuel in the oil and very thin.

 

Are the plugs wet with gas? Chances are they are contaminated just like your oil--change both!

Usually "run rich" is caused by too much air which sends a signal to the computer to send more fuel which doesn't get burned so it goes into the oil and fouls the plugs!

Look for an air leak!

The air valve is NOT supposed vibrate.

 

Hi fartoright. Cool name. I like it.

As to your oil being very thin. Is the engine cold or cooled down when you check the oil? Hot oil will be thin. The fuel in the oil is a sign of worn piston rings. Check to see if the oil on the dip stick will light with a match or lighter. Don't do it near other flammable stuff or inside. If it lights up easily than yes you have fuel in your oil. And do it only while the engine is cool.
And don't hold the match or lighter under the dip stick long, a second or two is long enough.
A ring job will be required to correct the worn rings. But to get you buy for a while may I suggest you change your oil and use a heaver oil like 15/40, and add some Oil Honey, I think it's made by Gunk, but it may be an STP product.
The idle air control control valve may have a vacuum leak. Make sure all clamps are tight, and the wire plug in leads are not corroded.