I have a 2003 Monte Carlo LS. I put a new fuel pump in about 2 or 3 months ago. Ran just fine till about a month ago. Started running rough. Misfiring. Took it to my mechanic. He plugged it in and cylinder 5 wasnt firing. He cleaned out the injectors and it ran rough for a couple days till the injector cleaner did its job and was fine till last week. Now it doesn't want to start most of the time. I replaced the starter and its still doing it. Its like rolling dice. It will start up fine sometimes but most of the time it won't without a lot of trying, killing the battery and having to jump it. Also, sometimes it will start but then just sort of struggle to get gas and stall. It will do that a couple times and then start right up like nothings wrong. There is no check engine light. No security light. I don't have a chip in my key so that isn't an issue. I'm very frustrated trying to figure this out. I'm also broke due to losing my job 2 weeks ago. This is putting a damper on me being able to find a job. If anyone can help me figure out what's wrong, I'd appreciate it. Thank you

 

Similar problem I had with my 04 Monte Carlo; I changed the Crankshaft Position Sensor located behind the harmonic balancer and now it runs fine. I hope this info helps you.

 

Replace the fuel filter.

 

This is the ignition problem they pretend doesn't exist. Long ago, I replaced my ignition and had zero problems after that until this week. Last month, the "recall" said I needed new keys. Today I couldn't start my car. This happened years ago as well. I'd be out somewhere, go back to my car and it wouldn't start. After replacing the ignition, never did it again until they replaced the keys. And the ironic thing is, now that they replaced the keys, and the car doesn't work, you're out of luck. You have to pay for a diagnostic, recoding your keys and it still doesn't stop the problem. I am so tired of Chevy screwing me out of money while not fixing the problem.