Car sometimes starts. Thought it was fuel pump but mechanic reset cpu and it started

Car is 2001 Pontiac Grand Am GT1 V6 So my car was starting with a long rumble and then didnt start but would sometimes start. Yesterday it didnt start at all and I had a mobile mechanic come out. He sprayed stuff in the engine and it started so looked like it wasnt the engine but something with the fuel pump or line or filter. Then he reset the computer by taking off the negative and having me turn the car on and off and when he rehooked it it worked. This was after trying to start the car for about 45 minutes so he said it is either a circuit somewhere for the fuel pump or he thought it was the knock sensor. I think its probably a circuit. He checked the fuse and it looked good but I am wondering wheres the next thing I should check? I dont want to replace the fuel pump if its a circuit somewhere else. Also there is no security light on so I dont think its that. Thank you for your thoughts!

I would suggest that it is the crankshaft position sensor. If it fails, no fuel. It can fail intermittently, usually with heat, though. They are usually cheap but sometimes hard to reach. Not sure about this engine.

It IS a GM car from the early 2000’s and the fuel pumps are a bit dodgy in that era. If the car has 100,000 miles or more, even more likely. Next time it cranks and refuses to start, whack the bottom of the fuel tank with a rubber mallet or small 2x4 and see if it starts. If it does - change the pump.

And you might consider avoiding that mobile mechanic. A knock sensor is not going to cause a no-start condition.

So it wouldn’t start, then the computer was reset, and after that it started and ran as good as new? Presumably still starting & running fine? hmmm … I think while it is still running I’d be checking the fuel trims, might provide a clue what’s wrong. Since spraying starter fluid into the engine made it start and run (presumably briefly), one idea is you got some bad gas in the gas tank. Water will go to the bottom of the tank & is the first to be sent to the engine. So maybe now the water in the tank is all gone. Given the outcome of the starter spray experiment, doesn’t sound like a crank position sensor to me. That would prevent spark too, so it wouldn’t run with starter spray either. Has the check engine light appeared recently, either currently, or before all this started?

Hi thank you all for your responses. So yeah it is still running fine now but it will likely get to the point where it wont start again as it has run before and then not been able to start. So i brought your thoughts to the JustAnswer guy and looks like im getting closer to narrowing it down.

Heres what he said

"Many of these possible causes mentioned should store codes as well as running issues once it has started, none of which you are getting.

CKP sensor would cause no spark, no start

Fuel trims would cause lean or rich codes and more so affect running, not starting

Knock sensor is not used till it has ran a while, it will not affect starting.

Since starting fluid helps, that tells me there is a fuel related concern. Either low pressure, worn injectors, or it is flooded from bad injectors. I do recommend a key on and engine running fuel pressure test to see if the pressure is low. Then I would have the injectors flow tested."

So it sounds like its likely the fuel pump or something connected with it but its just weird that once the CPU reset it worked right away? Sounds like the wiring to the fuel pump?

Thank you again for all your responses. I dont have much money as of now so getting this guy going is essential!


Keep this on your list.

The engine could indeed get flooded and cause a “cranks but won’t start” if an injector leaked fuel into the engine when the engine was turned off. But if that happened the engine wouldn’t start using starter spray either. I’m doubting that theory. In any event injector problems are a pretty uncommon thing, at least from reports we get here. You could try a can of fuel injector cleaner in the tank, inexpensive, & might help or at least provide a clue. Ray has mentioned the Techron brand on the show as I recall.

Another idea, if you think the engine is flooded, holding the gas pedal all the way to the floor during cranking will often get it to start and run. The powertrain computer software is programmed to recognize that sequence as the driver trying to start a flooded engine; so the computer turns off or limits the amount of gas sprayed from the fuel injectors.

Hey alright did a few tests today. Did the fuel pressure gauge test and when it was on the on position it had 0 and when i i turned it on it cranked but did not turn over and was 0 . I listened to the fuel pump in gas tank and it made a noise the first couple times but then stopped. I switched the fuel pump fuse and the car started right up (went to 25 on the on position and 50 when turned on) so i assumed it was the fuse. Bought a new fuse and it just started the first couple times but the last time it had trouble. Took a while and then with gas half down it started. And this last time it did not start. Not sure if there is something connected to the fuel pump fuse that could cause it to short that might be causing it? Or maybe the gas is affecting the sensor , only thing it has had the long start for a while. Since i got it. The guy said he thought it needed new spark plugs. Oh also when it would not start at all it said the gas was empty when turned to the on and when trying to turn it on but now it says its at the half a tank both when turned on the on position and turned on. Got excited for a sec and thought i got it. Thanks again for your insights. Is helping narrowing it down! Cheers!