Hello, I am new to this forum and need help! I have a 2001 Montana with the 3.4 engine. The car runs and then just dies, won't start sometimes and will idle for hours at other times. I have changed the fuel pump and filter, plugs and wires, all 3 coils and ignition module, replaces PCM, every sensor on the engine, both crank sensors, cam sensor, throttle position sensor, air intake sensor, Map, MAF, EGR Valve, everything on the engine I know of besides the knock sensor. Also have all new fuel injectors.
The engine can be running fine and then just cut out or start to judder like I am out of fuel, other times like it has just turned off clean, the tach will go to 0 and then without changing the key position it will look like I restarted the car with all the dash lights flashing. I am beginning to wonder if it could possibly be the ignition switch with the key sensor being intermittent?
I have checked ground connections on most sensors and the 5V power circuits. Cleaned the ground connections I have found but nothing has really been very dirty at all. The car has about 220K on it but it is the second engine and it was a crate engine from GM, so it is only about 65Kmiles on the new engine. The original engine did the same thing but almost always if it had rained or when it was very high humidity. It would go away then if I could get the engine to warm up somehow, but now it has nothing to do with water, I am in California and it not wet anywhere or even damp when it happens. Oh yes the car would show no dtc codes related to this. It would never throw a code or show the check engine light.
I have a Actron CP9580 scanner and was watching it run and every sensor seemed to be working correctly from the list it will show and then it just cuts out.
Just for those who wonder I also have a 1967 Firebird. I wish the Montana was anything like working on the old bird which anyone can fix.
By the way I was a smog and front end mechanic when I was much younger and know my way around a car, but this one is really got me stumped. Done everything on a car except for upholstery and that includes body work and custom body work and building kit cars and tooling for them years ago.