I have a 2003 Pontiac Grand Am, 3.4L V6. The engine runs perfectly as long as it is kept hot. If allowed to cool completely it will crank and crank all day but never fire. However, if I disconnect the battery for at least 30 minutes and reconnect it, it fires right up every time. I have good fuel pressure when it will not fire, but it seems as if the injectors will not fire. Suspecting the injection driver, I replaced the ECM/PCM. The exact same problem still exists. Anyone have any experience with this problem?
Have you tried to spray some starter fuel into the air intake when this happens? If so, will it start up then, at least briefly? That would be an important clue. the other way to find clues is the diagnostic codes. Anything posted in the ECM memory? Is the CEL on?
My first guess, the engine coolant temp sensor has failed, stuck in the “hot” condition. That’s what tells the computer if the engine is warm or cold. If the sensor fails hot all the time, then the computer won’t inject enough fuel to start a cold engine.
So why does disconnecting the battery help? Because the computer learns by doing, from the O2 sensor feedback. It has learned it needs to inject less gasoline than it would otherwise think it would need, based on what it thinks is the engine coolant temperature, hot all the time. When you disconnect the battery , it forgets this training. And then for a while at least injects the proper amount of fuel.
Do you have an aftermarket alarm system?
When starting a cold engine, the computer needs four primary inputs.
*Mass Air flow/Manifold Pressure.
The O2 sensor(s) don’t come into play until the engine has run long enough to where the computer goes into the closed loop mode to start adjusting the fuel trim.
Another thing to try is, when the vehicle sits, turn the ignition switch to the run position for two seconds and then turn it off. Repeat this a half dozen times and then try starting the engine.
If the engine starts right up, the problem is probably with the anti drain-back valve in the fuel pump assembly.
I will look into the coolant temp sensor, that is a good thought.
No codes show up, so no CEL. No aftermarket alarm, and in case anyone suggests this it is not GMs Passlock system either, as the security light is not on, and just in case I did try a key relearn several times.
I will try cycling the ignition as well, but that will have to wait till tomorrow.
Thanks for all the ideas so far, if anyone else has a thought I would welcome the help.
Well it wasn’t the coolant temp sensor. I doubt it’s the fuel backflow check valve as that seems more like it would be time dependent not temp dependent which it definitely is.
Then the problem might be with the crankshaft position sensor.
These sensors can be effected by temperature where the engine might not start.
Take a hair dryer/heat gun and heat the sensor up to see if the engine starts.
Replaced both crank sensors, still nothing. It will start with ether. It has good fuel pressure so something is keeping the injectors from firing.
hmm … well, what would cause the injectors to not fire when cold, but fire ok when warm?
One idea – I’m not saying this is a good idea mind you – the computer won’t pulse the injectors unless it senses the engine is rotating. That’s a safety function built into the software, don’t want to inject gasoline if the car gets in a crash. Usually it won’t turn on the fuel pump either unless it thinks the engine is rotating. So that would lead back to the crank sensors.
I think it is possible for the crank sensor to be good, but it still not to work, b/c what it senses is bad. If I only knew what the crank sensor sensed … lol … I think it’s usually some kind of pattern, probably magnetic, on the flywheel. I wonder if somehow that has been chipped off for some reason? Sometimes shops doing a clutch or transmission job will get a little overenthusiastic cleaning up the flywheel, and damage whatever it is that the crank sensor senses. Has anything like that happened recently?
The problem w/the above theory is that if the crank sensor function is on the fritz, not only would you get no fuel injection, you usually wouldn’t get a spark either. But you seem to be getting a spark. Just no fuel injection function. Ok, here’s another idea. Bad fuse, or bad relay, the one that powers up the injector circuitry. It’s possible for a fuse or relay to be affected by heat, and completely disconnecting the battery might cause the computer to reset circuits that otherwise wouldn’t be reset, and that might affect a cracked fuse or sticking relay. If you have access to the wiring schematics, check for any fuses or relays in the path that powers the injector circuitry.