I have been working on this for a while checking my ignition system and fuel system trying to find this miss. I have checked my icm and coil and they are both reading fine. Replaced plugs and wire which were pretty new. If I disconnect the battery and reset the computer then the car runs like a champ and has no problems then as the car warms up the miss starts. I get a p0300 code. The car stubles in low rmp and then as I get on the throttle the miss goes away and you can feel the car surge back to life and pull hard again. I took my car over to a buddies house to scan it and on the way it was missing like normal and then it started snow flurries and the miss got worse. Any help is appreciated. I have searched the forum for the p0300 code and got a lot of help but I am hoping that it is not the opti but am leaning towards it. Please correct me if im wrong. Thats all i can think of off the top of my head sorry for the long post and I if you guys have any question feel free to ask.

edit: New o2 snesors, you can smell it running rich and the scanner reads .4 volts approx on both o2 snesors. The o2 sensors are further back and have extensions on them because of the long tubes does this change anything? I have been told that it will affect the numbers the computer reads from the o2 sensors.

Thanks for the help in advance,
Joe

 

I thought if the 02's were to far back and weren't heated they would not work correctly. There are way to many things that can fix the p300 code. I would check for things like a burnt plug wire. Reading all the posts made me think it could be the opti but many replaced and it was something else. Lot of money and time for just guessing. I would do the cheap stuff first and see if it helps.

 

You have to scan it further to see if all the cylinders are misfiring or just one or 2. If all are misfiring, suspect something that is common to all cylinders like a coil or rotor. If only 1 or 2 are missing then suspect something only common to those cylinders like wires or plugs or even dist cap.

Check the coil for tell tale white spots on the insulation. This is shorting. You may even see it in the dark at night. Which you should be looking at anyway.

Since your problem is more prevalent in damp conditions, I would focus on wires. Look under the hood and under the front of the vehicle as well but your best bet is to scan a little deeper to find out which cylinders are missing.

 

I had the p0300 error code once. It was a loose throttle plate (throttle body top cover plate - A BBK twin 58) vac leak. Screws were loose. I noticed a rubber gasket under the plate. Hope this helps. B.

 

Which of the 4 O2 sensors on your car have steady readings of ".4 volts approx"? Under what conditions do you see this value? Does the voltage ever change? For example, on cold start the O2 sensors will read ~.450 Volts, because they are cold and not working. As they heat up, if you have a working AIR pump, the volatge will drop close to "0", then the PCM will kick into closed loop, and the pre-cat O2 sensors should start cycling rapidly (9 times per second) over the range 0f .0xx - .9xx Volts. If they aren't cycling like that when the engine warms up, and are stuck at 0.4 Volts, you have a problem.

If your O2 sensor extensions have poor splices or connections, it can throw the voltage rreadings off. If there is leakage between the +12V power supply wires for the heaters and the O2 signal wire, it will screw things up. Well-made extensions will not affect sensor readings. Poorly built extensions will screw them up.

His signature shows he has a 96, and the Pxxxx format confirms he has an OBD-II setup. All O2 sensors from 94 on up are 4-wire heated sensors. If his extensions are faulty, it might cause the sensors not to heat up, but there are codes for faulty heater circuits.

 

First of all thanks a lot for the help guys. Second i looked at the plugs and wires and they look fine to me nothing burt. The o2 extensions are pair i bought off of summit but i dont know how to go about checking them like injuneer is talking about leakage. How do i check this? And the car does not have a functioning AIR pump cause the headers didnt have a hook up so i removed it. Also the o2 sensors after the car warms were still reading between .38 and .54 on the scanner i was using on both o2 sensors these are the 2 before the cats the rear o2 are simmed. so if you say that it is a problem what could this be? Sorry a little inexperienced with these things. Thanks again for the help i am going to go back over and scan it again today. and will post with more information shortly.

after i scanned the car again i saw a p0305 code cylinder #5 misfiring i turned the car off to look at the plug and wire boot since it was easy to access and nothing looked out of ordinary and when i restarted the car then the code went away and never came back so im baffled. I hooked up a different scan tool and this the information i got these values are all from idle cause i didnt have someone to read the scanner while i drove hope these help

O2S11 (V) .09 - .90
ST FTRM11 (%) -3.4 - -1.6
O2S12 (V) .430 - .835
O2S21 (V) .005 - .45
ST FTRM21 (%) -3.4 - -1.6
O2S22 (V) .435 - .805
IG ADV (DEG) -18.0 - -12.0

I dont really know what these values mean in terms of whats going on but i hope you guys do thanks alot again

 

With the engine fully warmed up, what do they read? Are they steady (voltage somehwere in the range of 0.38 V to 0.54 V)? Or is the voltage jumping around rapidly? Are they swinging all the way from .0xx Volts to .9xx Volts or are they only covering the narrow range from 0.38 V - 0.54 V? You can determine if there is a voltage problem by looking at the voltage on a scanner. If the data you gave us is accurate, you have a problem.

We can tell you what the voltage is supposed to look like. You have to look at the scanner and tell us in some detail what the readings are, and under what operating condtions.

 

the voltage is jumping around rather quickly. the voltages on the number 1 o2 are moving through out the whole voltage range but the #2 sensor wont read any higher than .45v. those readings are from when the engine was fully warmed up operating under no load and idleing at around 900 rpm i got a pretty crappy scanner and this is all its giving me i cant get anything else out of it except those readings, what do you think about the codes its throwing? and why did the p0305 go away?

 

the missfire probably was from a loose wire at the plug thats why it went away when you put it back together. You probably have a bad O2 on the right side or a bad extension, also check if they have melted to the headers (harness).