Having problems with my 95 Bonneville, it stalls on me while I'm driving. It only stalls after the temp reaches 200 (which I understand is operating temperature?). The engine light used to come on, but doesn't always and hasn't recently.

Took it to a mechanic, he replaced the bypass hoses and fuel pressure regulator, didn't fix the problem. Took it back and he replaced the crank position sensor, still didn't fix the problem $500+ later. Got the coal pack tested, that wasn't it. Another mechanic thinks it'* the intake gasket, another says it'* probably the fuel pump. Auto part stores can't run a diagnostic. Researching the problem I found it could be the ECM, as it'* a notorious problem with 95 Bonnevilles, and I wanted to go that route in fixing it. Got an ECM from the junkyard for $30, came home, replaced it and put the original chip in it but the car wouldn't start. It would crank but not turn over. The most recent mechanic (a guy who just works on cars, not certified) said it was no good (but I sense he hasn't worked with ECMs much because he originally took out the brake ecm & had to ask the guy at the junkyard where the ECM was located on my car) , but researching today I found information about ECMs needing to be reprogrammed in some cases. Maybe it'* still good.

So I need some help. Does the ECM need to be programmed first? Other cases I read about the ECM being replaced on Bonnevilles mentioned nothing about reprogramming it, but maybe this is understood and something a novice like me has no idea about. O'Reilly can reprogram it for around $70. Wondering whether I should have them reprogram the $30 ECM and try to install it or if I should get a new one for $140 which would then still have to be reprogrammed and installed and HOPEFULLY fix the problem. I've spent lots of money and time on this problem and I want to take the most direct and inexpensive route to getting it fixed. Any advice?

Your correct, some 95 PCM'* are a little faulty. Which ones? I don't think GM ever gave a specific range of CAL ID'* that are faulty. And most stores cannot read the 95 PCM'* because its technically OBD 1.5, and not OBD2 as the connector would suggest. There is 1 particular model of Actron scanners that can read it. Not cheap, but WELL worth the investment and what it costs to run back and fort the the parts store to have them read it.

At this time, I would suggest taking it to the dealer to have the codes scanned. Its going to run you around $75 to have it done. This will give us a starting point on what might be going on with your car. Otherwise, we could be here for 10 pages replacing this and that.

Mechanic2'* diagnostic read that it was the fuel pressure regulator, then the crank position sensor, while Mechanic3 said he ran a diagnostic & didn't find anything, plus he couldn't get the car to shut off on him. I'm just afraid I'd be wasting my money on another diagnostic. . .would this PCM problem even show up? I'm confused by the fact that none of the mechanics have been able to diagnose the real issue.

If your check engine light came on, then there would be at LEAST a history code, unless the battery was disconnected. So I'm confused that the mechanics didn't find anything.

I should have asked this in the beginning. How long have you owned the car, how many miles and what has been replaced/repaired since you have owned it.

Can you remember, when the engine was at 200F, did the check engine light flash and did the engine seem to maybe stumble a little bit?

I've had it since 2009 and it has 177,000 mi. I did have the ECM replaced several years back, maybe 2010 or so. I don't remember what the car was doing at that time but the last time I had an issue with the car dying on me while I was driving it had to do with the battery connections loosening up.

In addition to replacing the ecm once, I also have had the alternator replaced, head gasket, and the recent fuel pressure regulator, bypass hoses, serpentine belt and crank position sensor.

When the car reaches 200 sometimes the engine light comes on, but not always. I haven't noticed any changes in the engine while driving, but it doesn't idle smoothly. . . not sure if this is always an issue or just as it approaches 200f. It seems to kind of surge and then come back down and the RPM hand goes up slightly.

I think we may be getting somewhere, BUT don't hold me to anything yet. LOL.

Go out and open the hood, remove the engine cover if it has one(remove the oil fill cap) and look on top of the big black thing. Right on top, you can see stamped in, like this one...




If you can, get me the date off of the top of this please.

did they check the ign control module while it was hot?

Is the oil milky? When it hits 200F and the thermo opens it could be sucking in coolant if the intake gasket popped. You know if you have a newer style metal intake gasket or the old crap plastic one? should be able to sneak a peak in there and see.