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This is a 1995 Buick LeSabre with a 3800 engine, fully loaded vehicle. Only has 30,000 miles on it - a real gem of a car. The original symptom was an intermittant engine shut off, hard to start then, and the door locks and electronic ride control rapidly cycling. There is no trouble codes in any electronic module. You might start the engine, drive for 5 miles, shut it off, go grab a coffee, come out, start engine, take off, get a short distance and all a sudden the engine shuts off. Every light in the dash is on. Turn key off. Engine may or may not start. Eventually it starts, runs fine for a minute or so. After awhile I get back to the shop. It gets bad enough the car can't be started and moved off the spot - the engine will not stay running. A short time later, it will start and run fine, maybe all day. I checked the grounds under the ignition module as they are notorious trouble spots. They are clean and tight. Even loosened them to make sure. What is really puzzling is when I plug my scan tool into the ALDL all four power door locks cycle once. This thing got an issue and I need help before I turn this thing away.

Have to go with a remote starting system or a bad pcm. Is the pcm under the hood by the fender? I remember running into huge programming issues with these. My sister in law had one and i would have to reboot the pcm twice a tear and finally had to replace it with a new g.m. one, reman was worse. Another thing that is tugging away at my grey matter is i believe the security module needs to be replaced when the pcm is and burned separate. Again, it's a bit foggy but i recall i needed two separate up loads into my tech 2 to set the modules. It was a real pain in the a** and there was a small probability of failure.

Look in the power distribution box under the hood for any additional wires and i believe (another foggy memory) that where the harness loops under the drivers side inner fender, if it applies to this model, it fills with water and it's right where a bunch of wires are connected, i believe they're tan. Another issue with g.m.'s is where the harness runs along the radiator core support. A few extreme times i've seen wires pulled away from connectors in the fuse panel. Good luck, i remember having night mares because of these..........................

Had it running earlier this morning. After about 15 minutes, it shut off. Started right back up. Ran a few minutes, shut off. Started right back up, after a few minutes shut off again. I installed spark tester between ignition coil and wire. Right when engine shuts off, it loses spark. Fuel pressure never drops. So evidently, what is happening is the PCM is shutting down the module.

Sounds like the ignition module itself going bad. I have also had crank sensors do this to me. Maybe scope the crank sensor alongside the ignition module...see which one drops out first.

Starting to see lots of these with the harness to the crank sensor bad due to oil damage where it goes behind the water pump. Makes the same symptoms as you are having, hard to duplicate when running correctly. Napa keeps the sub harness around here.....

I suppose what I need to do is get my trusty lab scope out and do some scoping tonight.

Oh boy..................

Just a thought or point here since you mentioned lab scope. The Snappy scanner will do wave form comparison now and shows a good sample so you can compare. when the scanner is hooked up and the vehicle is failing i run the movie option and then i can run a communication cable from the scanner and use a T.V. screen so even a blind person like me can see. Sometimes i feel like Agarn from F troop. When i'm looking at circuit boards for cracks or bad solder points i sometimes get caught with three pair of glasses stacked one on top of the other so i can see fine details. As soon as i look away at something else i get a wicked head rush.......

We finally found the problem. It was in the secondary lead from the positive battery terminal to the power distribution center in the rea rof the engine compartment. Just off the battery inside the insulation is was all corroded and rotted away. I replaced the cable and it was fine after that.