1996 Cavalier - cylinder 4 misfire, barely runs

[Steph]

:help:

About 3 months ago my check engine light came on, and the code was P0403 (cylinder 4 misfire). At the time it seemed to be running fine, but got very rough shortly afterward. The first thing tried was to replace the spark plugs and wires, which made no difference. Shortly after that it started to have poor acceleration before being warmed up, a couple days later it just wouldn't start, so it was towed to the mechanic who replaced the fuel pump. So now it would start again, but still had the light on and was running rough. After trying to self diagnose the problem with the Haynes manual I took it back to the mechanic. They couldn't tell me what was wrong with it. They said that they heard pulse to all of the injectors, so assumed they were working. They checked the pressure and said it was fine. They replaced the coil, and it made no difference. The only idea was maybe the ignition control module, but that was just an expensive possibility. Rather than do that I just ran a bottle of fuel system cleaner through, and it helped! The check engine light turned off and it was running beautifully.

Two weeks later it came back on. But it was still running smooth.

Three days ago I suddenly started having trouble starting the car. It would turn over, but didn't want to start for a few tries. A couple of times it started but then stalled immediately. So I let the car sit over the weekend because I was afraid of ending up stranded somewhere. Today I wanted to take it in to Autozone to get the codes pulled just to make sure they were the same, but my car had no acceleration. It would get up to about 20mph, but that was it. It felt like it was almost out of gas, but it wasn't. I drove it around the block, and then a parking lot for a couple minutes, and it starting working well. I had to turn it off at Autozone to get the codes (the same one), and then it didn't want to start again! After a few tries, and a couple of stalls, I gave it a lot of gas as soon as it started so it would stay running, and I heard a loud "pop" from the front. I was only a couple of miles from home, so I thought it would be ok to get home. Instead, it wouldn't go above 10mph, and that was with a lot of pumping the gas peddle or flooring it, which caused the same "pop". At that point, holding up traffic, I managed to turn (at about 2mph) into a parking lot where the car now sits. :cry:

Thank you for taking the time to read all of this and I appreciate any ideas of what the problem could be, or things I can check to narrow down the possibilities.

[2strokebloke]

Good compression? Good leakdown? Perhaps sticking valves or clogged fuel filter?

[Steph]

I think the mechanic told me I had good compression, and the fuel filter should be fine since it was replaced with the fuel pump. Not sure about the others.

I did have one other symptom to add that I am hoping will help. Yesterday when I brought it home from the parking lot, I was able to get it up to about 30mph by pressing very lightly on the gas. Giving it any more would cause it to slow down again.

I have also looked up the symptoms of a bad ignition control module, and they seem to match a few of my problems so I am now giving this more consideration. I was wondering if anyone else has ever known of that being a problem??

Thanks again.

[Steph]

One more thing to add...

Today I disconnected the battery long enough to clear out the codes, and tried the car again. Would you guess, it worked fine?? I am assuming that means that there isn't really anything physically wrong with it, that it must be a computer problem? Does anyone have any ideas if that would be a sensor or the maybe the ignition control module my mechanic wanted to replace a couple of months ago?



Once again,
Thanks for any and all ideas, and I will post the outcome if something does finally fix it for good.

[Steph]

Well, the problem is fixed. It was the fuel pump of all things. At least it had a lifetime warrenty.