[quote name='ModMan_70' timestamp='1321495170' post='11214755'] My car did that after the Camshaft Position Sensor (CPS) failed. But, I did get a Engine Light for that. What happens when the CPS pukes out....and correct me if I'm wrong.., Is that the computer looks at the Crank Sensor to perform the fuel and ignition timing. When the computer looks at the crank sensor alone to perform timing, it either lucks out and gets it right....or the piston will be off by 180 degrees and the car will never start until you give it a break and try again. [/quote]
Close, the Computer ALWAYS does the ignition and fuel timing off the Crank Pos Sensor. It needs the Cam Pos Sensor to sync it, since a 4 cycle engine does 2 crank revolutions for each full cycle of all the pistons.
If there is no signal from the cam position sensor, it just guess's, and it has a 50/50 shot, if it guess right, then the motor runs fine. Since the Neon has a wasted spark ignition system, guessing wrong and being 180° off doesn't effect ignition, it was going to fire the spark plug on the exhaust stroke anyway. It does mess up the fuel timing, but the motor will run, although very poorly, if you inject fuel on a closed intake valve and then the valve opens later and sucks in the puddle of fuel.
I've have seen multitudes of posts about fuel pumps starting to fail by intermittently quitting, but coming back and run again for a little while. Same for Crank Pos Sensors, without throwing a fault code, people have had intermittent lose of signal, which kills the ignition and fuel, only to have it come back later and have the motor run fine.
- Check for Fault Codes, fix what every codes you get and see if that solves the problem.
- Perform tests on the Fuel Pump, Crank & Cam Pos Sensors (Keep in mind, since this is an intermittent problem, the offending part might pass the test with flying colors and then just fail for 20 minutes again out of the blue). Also check out and test the wiring, shorts in the wiring are often intermittent and a short to one of those items would be the same as the item being bad.
- Tests or Codes don't tell you anything, I'd replace the Crank Pos Sensor, that is the most likely and cheapest and easiest to replace.
- If that doesn't fix it, then the CAM position sensor, even cheaper and easier to fix, but less likely to be the problem.
- Before spending all the money on a fuel pump, I'd consider borrowing or buying a fuel pressure gauge and check the fuel pressure. It could be the fuel pump, but I'd hate to spend $220 on a new fuel pump and all the work to change it, to find out it wasn't the fuel pump causing the problem.
A crank or cam Pos Sensor wouldn't be such a big deal to swap out on a guess, hoping it will fix it.