1986 Volvo 740 turbo engine dies randomly without warning! Topic is solved

cosmiclobster · Post by **cosmiclobster** » 28 Aug 2005, 00:47

Hi. This is my first post here. Maybe my experience can help some other Volvo owners out there.
I have a 86 740 turbo wagon. I bought it for $600 because of some wiring problems (insulation falling off the wires!!) and the fact that it would stop dead in the road at random times.
After fixing the wires and replacing the cracked hoses and doing all of the other standard fixes, I was still having problems.
I suspected fuel problems, ignition problems, computer problems and anything else I could think of. After replacing a dozen parts from the junkyard I finally narrowed it down to the thermostat that takes preheated air from a shroud around the exhaust system that is used to heat the intake air when the engine is cold. This thermostat (and the air deflector mechanism that it physically moves) lives in the air intake box under the air filter.
The problem occurs when the thermostat is defective and stays in the preheated air position (or dosen't completely close off the preheated air source). After the engine is hot it keeps sending hot air into the intake and the Air Mass Meter gets cooked, which screws up the mixture so much that the engine can barely run.
You can verify that this is your problem by unpluging the A.M.M. This puts the computer into a "limp home" mode. If the engine returns to a normal idle with the A.M.M. unplugged, then you know that the A.M.M. is way too hot from the preheated air and malfunctioning (or that it has finally dies completely if the engine wont run correctly when first started when cold). A quick fix is to remove the aluminum feeder tube from the exhaust shroud and see if the problem goes away.

I'm happy to say that my Volvo with 145,000 miles has not stranded me in the last year after taking about 3 months to finally figure out what was going on.

Hope this can help someone out there!

merry kim · Post by **merry kim** » 16 Oct 2005, 15:15

i had this same problem, and it was the fuel pump relay located under the dash on the passengers side.

Guest · Post by **Guest** » 18 Oct 2005, 18:41

I had the relay problem too. When it dies you can flick it with your finger and it would then start right up again.

Guest · Post by **Guest** » 18 Oct 2005, 18:42

I forgot to mention mine is an 88 fuel pump relay behind ashtray second row left hand side white relay.

Guest · Post by **Guest** » 27 Oct 2005, 18:21

if your tach drops to zero immediately when the car dies it may be your hall effect pickup in the distributor. My wife's 740 would stumble and die when hot but as time went on it got progressively worse. I think volvo calls it an impulse sensor. Please let us know what you find.

blubeard11 · Post by **blubeard11** » 31 Jan 2013, 21:02

I have a 85 volvo 740 turbo and i had hard starting (cranks for like 3 seconds then starts), it would stall at odd times while driving. the tach would drop to zero and then it would have to sit for a up to 3 minutes then start back up. it would stall at a stoplight or stopsign at random times. and it would idle rough and the rpms would go from 700-1100 rpms while sitting at a light. i did what was sugested bought a fuel pump/ fuel injector relay and a radio noise relay. i couldnt use the rnr so im out 12 bucks. but the 14 dollar fuel relay fixed all those problems. its like a new car.

Post by **billofdurham** » 01 Feb 2013, 11:54

Welcome to Matthew's Volvo Site.

Good to hear the site helped you. The radio noise suppression relay wasn't fitted to the '85 model.

Bill.