I have a 1996 C1500 with a Vortec 5.7l engine. There is an intermittent problem that is experienced only after the truck sits for several days. When attempting to start the vehicle after sitting several days, the engine will crank over and then experience resistance and stop. When tried again, the same will happen and after a time (might be 10-20 attempts) the truck will start and run poorly for 30 seconds or so until the situation passes. After this, the car runs great again.

When using the truck daily, there is not an issue. The car runs fine when operated daily. there is no missing, fuel economy has not changed, ....

The battery and electrical system (charger, cables, connections, ... ) is not the issue. There is a new battery also.

In past experince, I would see a problem like this (earlier cars) when the timing was too far advanced and there was preignition in the cylinder, causing a resistance that the starter cannot overcome. I have had the car into the dealership on several occasions, but they have been unable to diagnose. I am not getting any error codes that can be used to diagnose the issue. the latest experience working with the mechanic at the dealership had them focusing on a fuel injection issue, and they replaced the injectors (via warrentee). I am somewhat convinced that this is an ignition related issue with the timing and not a fuel problem.

I am starting to think that there might be a problem with the crankshaft sensor. I am not sure though why this issue would be intermittent and not occur every day if the issue is the crankshaft sensor.

Does anyone have experience with a problem like this or any suggestions? I am getting convinced that the GM mechanics are not going to be able to solve this one for me.