I recently purchased a beautiful 1986 760 GLE Turbo - the car has 159K on it, but engine was replace with a new factory unit at 91K.

When I bought the car I was told it needed a new Hall unit in the distributor. On the drive home it would miss, backfire, stall at highway speeds, when at lights, etc. I would restart when needed. It got me home (about 40 miles. It starts in the driveway fine and moves around fine.

Today I replaced the distributor with a used but working unit and took off on a test drive. The car ran beautifully for the first few miles, then I noticed some hiccupps, and as the car got warmer the problems started acting up again the same as the drive home.

What would you think my next course of action should be? I am somewhat mechanical, but not a gearhead or anything.

The car ran fabulously until it warmed up. Would love to find a Volvo gearhead in the Pittsburgh PA area.


Help

Well, I did the tap on the MAF with a hammer that I have read so much about, and took Ovlov for a ride (nicknamed Ovlov, I know real original) - and he never missed a beat. Ran like a bat out of hell!!!!! Not even a miss, hiccup or hesitation, nothing!!!!!

So do I put a new one in or did the tapping it clean something off and it's fine now?

I'm feeling like this right now because that was the first ride in it that I HAD A BLAST!!!

Check the connection pins. They have been known to push back out and not make good contact. You can clean it with some carb cleaner, dont brush it, use air to clean it off.
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Today I warmed it up to operating temp, put it in drive (of course blocked and emergency brake on) and commenced to "mess under the hood. I followed and checked vacuum lines, no leaks found, one was soft and needs replaced as it could collapse, but I squeezed it shut and it made no notible difference. I followed wires, messed at junctions and terminals trying to see if messing with them would cause any noticable hiccups with the car. I had already pulled some plugs and cleaned them and put them back in place.

In it's own after it got warmed up, it would on occasion stumble, and stahl, or stumble and then surge. I verified that the tach is not bouncing or noticably affected by this when it happens.

I assume since the tach is not being affected when it's having it's little siesures that I can rule out the Hull sensor?

I had much the same stalling-when-warm issue as you. My car is a 1989 740T. I used to drive it for a while a then call the NRMA (the Aussie NSW equivalent of the AAA) for a tow!

According to the 700/900FAQ, stalling when warm could be due to a bad hall sensor/insulator connector, or the ignition module, or the FI/Noise suppression relay.

In my case, a really bad hatchet job on the hall sensor by the previous owner/mechanic was a big issue and the varying tachometer speed at idle when warm was symptomatic. But since I didn't know if it was going to be the one component or the other, I changed out the FI relay and the ignition module at the same time for peace of mind. Also put in a new distributor rotor and cap plus new spark plugs.

BTW, the position of the distributor as well as how it actually fits into the matching hole in the engine is rather important. I first put it in without checking that the alignment is similar to the old one. Bad - engine misfires/starts for a while and then stops. Since I couldn't remember exactly how the old one fitted, I chose a 'somewhere inbetween' alignment. It's worked fine after that. [This whole exercise took forever since the dist/cap/rotor had to be taken off and replaced and then all over again a few times round, within that horrible confined space at the rear of the engine]

The heatsink or base of the ignition module has to contact the car chassis flatly since it uses the chassis to dissipate heat. It helps that the screws are tight and heatsink compound or paste is used - I had to use slightly larger screws to ensure that this would be so since the old screws didn't fit tightly anymore for some reason. The ignition module is right next to the battery. It's trapezium shaped with a multiwired plug connected to it, and it probably has the "Bosch" brand.

I bought all my parts from FCPGroton.com.

The other thing that I have done, given that mine's a turbo car, is to change out almost all of the old intake/intercooler and vacuum hoses. It helped a lot. Most of the intercooler hoses were soft from oil and heat. The vacuum hoses were literally crumbling. I used as many silicone vac hoses as possible.

http://i277.photobucket.com/albums/kk80/My3buicks/DSCN0326.jpg

I worked on it a little today as I didn't have much time. I found a vaccuum line that had a bolt plugging it. It went to (now here goes making a complete idiot of myself) a thingy on the front of the engine that had a rubber hose going into a bigger hose/pipe that went to the turbo box. I took the car out for a drive, and again it ran great until it warmed up, and then same symtoms, but I must say, not quite as bad. I also watched the tach when this occurred and there was no eratic needle movement.

First thing is that year group falls into the engine wiring harness rot. Do a google search for Dave Barton, website. He sells harnesses, and also has a FAQ on how to identify if yours was replaced. Turbos hate any type of air leak. Go over your hoses carefully. Does your tach become erratic when this occurs? Thats usually the hall sensor. But since it only does it when warm, maybe AMM is going out. Pricey, unless you find one at a junkyard.
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