P0300 Cylinder Misfire Detected - Random Cylinders

[jkelley]

2000 Chevrolet Camaro 3.8L 5spd.. 130k

Throwing a P0300 code only:
probable cause: ignition system fault-spark plugs, ignition wires, coils; vacuum leak; injector fault; high or low fuel pressure

I was driving and my car feels like its sucking in air through a straw (shaking, bogging down, not accelerating quickly at all, sounds raspy and deep (sounds like a WRX STI), hesitating at low rpms like it's gonna die out)... help? TPS (changed 6 months ago)? Cat (changed 1 year ago)? Fuel pump? Fuel filter (changed 1 year ago)? O2 sensors? Sparks/plugs/wires (Changed 2 years ago). I've also noticed my gas mileage has been quite UN-economical

My girlfriend accidentally put 91 premium gas in my car (about half of a tank worth) about 1-2 weeks ago, could this be of any cause?

[Atrum Rosa]

Re: P0300 Cylinder Misfire Detected - Random Cylinders

The premium gas wouldn't hurt the car. I had to change the coils, plugs, plug wires, and the catalytic converter before this code went away. Exact same symptoms too.

[jkelley]

Re: P0300 Cylinder Misfire Detected - Random Cylinders

oh, i would think the premium gas may cause the spark plugs/wires/coils to go faulty.. =/

[Atrum Rosa]

Re: P0300 Cylinder Misfire Detected - Random Cylinders

While I'm relatively new to automotive science, I believe the octane only affects how easily the gasoline ignites. Higher octane is harder to ignite and less prone to detonation, which is why some very tight tunes require it. Unless you have really bad spark plugs, I imagine it would still fire off just fine, especially if it was only half a tank.

[ssms5411]

Re: P0300 Cylinder Misfire Detected - Random Cylinders

Higher octane will let you run more advance timing without KR, the car has 2 tables a low octane and high octane , if your car sees KR then it will use the low octane tables and when higher octane is used its a hotter spark so it will let you use more timing, so your car stays in the higher spark table which means more HP and TQ. I would think like said you have a a plug wire , coil or even it could be bad gas, I have had it before and it will make it run like crap, only thing to do is drain some of it or run it down and find a good gasoline gas station who is busy alot so they have new fresh gas coming in so often , then use 91 or higher, AZ is only 91 but there are places who sell 5 gal. 100 unleaded octane.

[jkelley]

Re: P0300 Cylinder Misfire Detected - Random Cylinders

So I Was able to troubleshoot my ignition coils and was able to find out that the furtherest coil rear of the motor was not igniting so I replaced it with a new one and after doing so, it still did not ignite. In order to eliminate that the coil that I used to replace was bad, I swapped the one not igniting to the one in front of the motor and vice versa and still the one furthest to the rear of the motor was not igniting. It became obvious that it was some sort of wiring problem, not the ignition coils themselves. So I looked at a couple wiring diagrams and saw that the ignition coils are wired to an ignition module and wires branch off from the ignition module to the crank shaft position sensor and cam shaft position sensor. What could be causing the furthest coil to the rear not to ignite? Could it be a short / open between crank position sensor and/or cam shift position sensor and the ignition module? Could it be a short from the ecu to the crank or cam shaft position sensor? Has anyone had this problem? Does anyone know where the crank position sensor and cam shaft position sensor are located, pics would be greatly appreciated.

[ssms5411]

Re: P0300 Cylinder Misfire Detected - Random Cylinders

ICM, the ign. control module the coils are sitting on.

[jkelley]

Re: P0300 Cylinder Misfire Detected - Random Cylinders

So you believe the icm is bad??

[ssms5411]

Re: P0300 Cylinder Misfire Detected - Random Cylinders

In other words it could be since the coils have no effect, did you OHM test the coils with a mutimeter, its a good way to check them and any sensor you think it is. I would check out the ICM first and go from there with a mutimeter , Iknow injectors are 14-19 ohms are good and the TPS ,IAC is like .5 volts is good, the Haynes manual will have the correct values for each sensor.

[jkelley]

Re: P0300 Cylinder Misfire Detected - Random Cylinders

It was IMC.. thank you

[Rob Bell]

Re: P0300 Cylinder Misfire Detected - Random Cylinders

Good job diagnosing it jkelley, so how did you determine that it was the ICM?

[jkelley]

Re: P0300 Cylinder Misfire Detected - Random Cylinders

So I Was able to troubleshoot my ignition coils and was able to find out that the furtherest coil rear of the motor was not igniting so I replaced it with a new one and after doing so, it still did not ignite. In order to eliminate that the coil that I used to replace was bad, I swapped the one not igniting to the one in front of the motor and vice versa and still the one furthest to the rear of the motor was not igniting. It became obvious that it was some sort of wiring problem, not the ignition coils themselves. So I looked at a couple wiring diagrams and saw that the ignition coils are wired to an ignition module and wires branch off from the ignition module to the crank shaft position sensor and cam shaft position sensor. What could be causing the furthest coil to the rear not to ignite? Could it be a short / open between crank position sensor and/or cam shift position sensor and the ignition module? Could it be a short from the ecu to the crank or cam shaft position sensor? Has anyone had this problem? Does anyone know where the crank position sensor and cam shaft position sensor are located, pics would be greatly appreciated.

By the post above^^ and then I decided to swap out the ICM. :naughty: