P0300-Random/Multiple Cylinder Misfire questions-Please help!

[quicky422]

I have been doing alot of reading to try to pinpoint this problem. I have a 2001 olds alero 3.4L with ~113,000 miles. I have had the ICM tested(good), the resistance of the coils are within range(5000-7000ohms), plugs and wires were installed about 8 months ago along with a fuel filter replacement (wires had a good level of resistance). I have tried testing the 7x crankshaft sensor but my tester does not have the range to display 200millivolts AC, which is what the book suggested. I have read almost all the posts in this forum that may pertain to this problem and have found nothing but more possibilities which really hasn't made solving this any easier.

Now I have a few questions:

1. Is it wrong to assume that if there is a bad sensor, that the PCM/OBD will assign a code to it if there is a code available to assign?
   • Therefore, the PCM/OBD can not assign a code for this problem because the problem lies in an area that the PCM/OBD does not monitor, right?
2. So, is it safe to assume again that with the PCM/OBD assigning a P0300 code that all the other sensors involved with the ignition process are working correctly otherwise there would be another code displayed in addition to the P0300 code?
3. So what other parts or areas can cause a P0300? the intake manifold gasket, clogged or dirty injectors, vacuum leak, faulty plugs or something else??

Any suggestions or comments about this would greatly be appreciated!! I took the car to the dealership but they only read the code and sent me on my way; no suggestions or helpful comments. They guard information on a topsecret level which is insane! I called that same dealership when I was replacing plugs because the car manual gave one part #, the Haynes book gave another and the parts store came up with yet another. I had three part numbers and nothing to validate with so I called the dealership and they wouldn't give me the correct spark plug part #. That's why forums like this are like gold!!

Thanks

[scoopy03]

Originally Posted by quicky422

I have been doing alot of reading to try to pinpoint this problem. I have a 2001 olds alero 3.4L with ~113,000 miles. I have had the ICM tested(good), the resistance of the coils are within range(5000-7000ohms), plugs and wires were installed about 8 months ago along with a fuel filter replacement (wires had a good level of resistance). I have tried testing the 7x crankshaft sensor but my tester does not have the range to display 200millivolts AC, which is what the book suggested. I have read almost all the posts in this forum that may pertain to this problem and have found nothing but more possibilities which really hasn't made solving this any easier.

Now I have a few questions:

1. Is it wrong to assume that if there is a bad sensor, that the PCM/OBD will assign a code to it if there is a code available to assign?
   • Therefore, the PCM/OBD can not assign a code for this problem because the problem lies in an area that the PCM/OBD does not monitor, right?
2. So, is it safe to assume again that with the PCM/OBD assigning a P0300 code that all the other sensors involved with the ignition process are working correctly otherwise there would be another code displayed in addition to the P0300 code?
3. So what other parts or areas can cause a P0300? the intake manifold gasket, clogged or dirty injectors, vacuum leak, faulty plugs or something else??

Any suggestions or comments about this would greatly be appreciated!! I took the car to the dealership but they only read the code and sent me on my way; no suggestions or helpful comments. They guard information on a topsecret level which is insane! I called that same dealership when I was replacing plugs because the car manual gave one part #, the Haynes book gave another and the parts store came up with yet another. I had three part numbers and nothing to validate with so I called the dealership and they wouldn't give me the correct spark plug part #. That's why forums like this are like gold!!

Thanks

something so simple as the firing order could be the problem but it could be more severe. make sure that the wires are going to the right cylinders that is a possible problem.

[horse727]

I had the same problem and it was the spark plug wires and one was even burnt I bought a new set and it was good to go

[quicky422]

I think I might replace plugs and wires even though they are only a few months old. It's easy and doesn't cost much.

On the other hand, I have been home more often and have pinpointed when the misfire occurs.

It seems to only misfire after starting the car after it has been sitting overnight. I thought that maybe the head gasket was leaking into a cylinder or two after it cooled down but after starting the car and trying to back up, the idle oscillates and eventually it stalls - it only happens in reverse though. All this only happens when the car is cold and has been sitting overnight. Once it has warmed up, it runs fine.

Any ideas?