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New Fuel Pump Check Engine Light On Idles Rough

Hi, my husband is driving our 1997 Chevy Cavalier and last week he stopped to get gas then the car wouldn’t start. I finally had to go get him and AAA dropped the car off at a mechanic that we were not familiar with since our mechanic was 80 miles away.

So the mechanic determined that the fuel pump was bad. We got the car back on a Thursday and by Monday it would not start again. We called the mechanic who said it could be moisture in the line. So my husband purchased some engine starter for clearing out moisture and new spark plugs. After 10 minutes of trying to start it finally did. The check engine light is one, it idles very rough, will occasionally backfire, gas mileage has dropped and when we were trying to start it it sounded like a small boom under the drivers sit where the fuel lines are but continued to run. So I am thinking something clogging the fuel and have to wonder if we needed a fuel pump in the first place. Also we have to consider when the fuel pump was changed that being an old tank maybe sediment rose to the surface and was drawn into the line when the tank was filled and the car started the first time.

So any ideas what could be wrong? Thank you.

You need to have the fuel pressure regulator checked to make sure it’s not leaking.


If I think a tire is low, I check it with a gauge. But still, at least I can see the tire and make an educated guess as to its pressure.

You can’t see the fuel. Please connect a fuel pressure gauge to the fuel rail and find out what the fuel pressure is.

That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

“Rough idle, backfire, boom under the driver” sounds like a LOT OF FUEL being dumped into the engine, and some of it burning (backfire and boom) in the exhaust system.
How can too much fuel be dumped into the engine? It can if: the fuel pressure regulator allows too much fuel pressure; if the engine computer commandes it of the fuel injectors; if fuel injectors stick open.
Each of these can be checked, without changing the parts to find out (which we will call Bad Mechanic Method).

We are going to take it Friday to are regular mechanic since it is obviously something we cannot check out ourselves. I will let you know what happens. Thank you!

Hi, thanks everyone for your ideas… after 3 weeks since we were snowed in we were finally able to get the car and it is running fine but the check engine light keeps coming on… anyway it had something to do with wiring and a coil of some sort…sorry I have not received the bill with details yet and my husband spoke to the mechanic so have I do have the correct lingo… I am not going to bother with the check engine light because I am not putting anymore money into this car!!! Thanks!

You state, “The engine is now running fine, though the check engine light is on.” Well, that’s good; but, you should get the check engine light read. It might be something you can put off, or not. Some auto parts stores will read the light, for free. I feel it may yield a code like P0420. This would be a result of all that fuel (from misfires) being dumped into the catalytic converter. Let us know.