99 Grand AM misfire

[trojancouch68]

my 99 grand am 2.4L is misfiring. I took it to Midas for their free check and 2 codes came up....P0302, the cylinder 2 misfire......and, P0128, something along the lines of insufficient time in the temperature loop....they said that the misfire was due to the P0128 code, and mentioned replacing the temperature switch, i dont even think the GA has a temp switch, feel free to correct me if i am wrong....how do i solve the temp. loop problem? is it an 02 sensor? a bad injector? any and all help is welcomed!!!!

[GTP Dad]

Actually the P0128 code has to do with the coolant temperature relative to the thermostat. It may be that your thermostat is stuck open and the engine is not getting up to temperature. As for the P0302 code you might want to pull the cover on the engine and check the plug on that cylinder. That particular code indicates a misfire on cylinder #2 and it may be plug or connector related. Easy fix. I really don't think that the P0128 code has anything to do with this misfire.

[trojancouch68]

i replaced the spark plugs, the boots, and the spark plug housing...all with ac delco parts......i was told by my local machanic it might be a bad fuel injector, i tested the injectors, all are clicking while the engine is running, dont know if there are any other tests to do on injectors to rule them out.....i was also told by the dealer that it might be the coil that has gone bad, so i switched the coils around and am waiting to hook the car up to the computer..................something to add........i noticed that when i first start my car, it runs fine, and then a few mintues later(a mile down the road) it starts to misfire, also when i really give the car gas, the misfire seems to go away as i accelerate hard, but then when i let off the gas after accelerating, it seems to go back into misfire mode??????.....any and all advice would be very helpful, im ripping my hair out trying to fix this nagging problem..thank you!

[oldmike]

Have you fixed the P0128 problem yet? Might want to fix it first to get it out of the picture. I don't understand the "spark plug housing". Aren't the coil packs under the large white plastic piece that the boot connects to?
Mike

[GTP Dad]

Based on your description this does sound like a bad injector. It could be dirty or it could be going bad. An easy test would be to change it with one from another cylinder. If the misfire location changes then the injector is the culprit. If not something else is going on. One other thing you may want to do is to check the wiring to the injectors. They can wear, burn through or just break. A frayed wire will cause problems like a bad injector.

[xeroinfinity]

trojancouch68, you can test the resistance of the injectors to see if they are working with in tolarances.

Ohms resistance should be 1.95-2.3ohms ,
and if you dont hav an Egr(which you do) it'll be 11.4-12.6ohms which is the same as the V6.

Good Hunting!

[gmack221]

Double check your getting spark on all 4 cylinders, all it takes is a regular set of plug wires & a spark tester, its possible to get a bad coil housing (i know it happened to me). Check the resistance on the injectors as xeroinfinity said, then check the 02 sensor (but I believe that would throw a different code). Other things you may want to check is mass air flow sensor & fuel pressure regulator (but i'd think you'd get the misfire on the end cylinder if this was the case). Have you changed your fuel filter? never a bad thing to do!

[jmartindba]

By chance, you haven't had the timing chain off for maintenance such as replacing the water pump have you? I replaced the water pump on my '99 GA recently and it had a horrible miss at idle afterwards.

Jeff

[Slade901]

Sounds like failing ignition coil housing to me $60. Do the cheapest thing first though.

[Kevro869]

My 2001 GT is doing the exact same thing. When the engine is cold is runs fine but as soon as it warms up a little it starts to misfire. My mechanic thinks it is the O2 sensor or carbon build up surrounding it.

[trojancouch68]

ok...i figured it was the O2 sensors as well, anddddd i replaced the sensors, and still giving me a misfire. i also changed the thermostat and fuel filter, still giving me misfire.....just out of curiousity, is there an easy way to check the fuel pump on my GA, its the 99 GASE 2.4L 4 cylinder

[trojancouch68]

i took it to the shop, the mechanic told me that it gave him a code...injector circuit malfuntion - cylinder 2 (P0202) along with the #2 cylinder misfire (P0302).....what am i dealing with, with the P0202 code?

[GTP Dad]

Could be a broken wire, bad connector, bad ECM. I would suspect a bad injector wire. They can get broken or frayed and they cause problems. Probably the cause of the misfire.

[trojancouch68]

...as if this wasnt getting fun enough!!!!

so i noticed now an odor of oil burning, so i look under the hood, and my air intake manifold is covered with a layer of oil on the inside....it is the black box in front of the engine block, not the black box that contains my air filter, but the black box that is connected to both the throttle body and the air filter box(possibly called the air intake manifold??).....i noticed that the rubber tubing that composes the PCV vavle thingy, was covered in oil, but the 4 cylinder doesnt have a PCV valve, so i dunno what to call that section of the manifold, but i was told that the whole black piece, that i think is called the intake manifold, is the reason for the misfire....who knows???? also another tidbit of info, i took off the intake manifold (black box thingy) and the car ran fine without it on, but when i put it back on, it began to misfire again.....
...just thought i'd try and get a lil more out of you guys, your help has been much appreciated so far, thanks