So a few months ago I purchased a 2000 Camaro with the 2nd gen 3.8. It ran great but was loud because someone did a muffler delete. I revved it up one day and it started running like crap immediately after and the CE light came on. PO300 code. It is the only light. This is everything I have replaced because I know it would not be a spark plug, or a wire or a coil because it would be 1 particular cylinder missing. I replaced, ignition module, all 3 coils, ignition module, fuel pump, fuel pressure regulator, crank and cam sensor, all 3 oxygen sensors, Mass Air Flow Sensor, fuel filter, all new spark plugs, wires. I took the timing cover off to see if it jumped timing, The timing marks are aligned. The misfire started after I revved up the engine. I am baffled. Does anyone have any idea what is could be?.

 

Tap the MAF sensor with a handle of a screw driver. Also wiggle the wiring harness going to the MAF sensor and the ignition model while it is running and listen for a change in how the car runs. Recheck codes to see if you got any new ones.

How does it run with the MAF disconnected? clear codes before hand. See if the 300 resets.

I am not saying this is what wrong with your car but I chased a random for 3 weeks. It was come and go. I was spraying the intake looking vacuum leaks and when I passed over the wiring connector at the MAF the car smoothed for a second. I shook wire and resprayed wire and it did not repeat so I assumed it was unrelated. The next day I bumped the MAF wire and it changed again. I ordered a new pig tail and I soldered it in. The problem was gone.

 

I replaced the MAF but will check the harness when I get home tonight. Thank you for the suggestion. I really appreciate it.

 

have you done a compression test?

 

I have checked the passenger side of the engine compression. As soon as I get the intake back on I will check the driver side. I am replacing the intake manifold gasket. If a cylinder had no compression wouldnt it cause a single cylinder misfire or would it be a random misfire?

 

be sure to replace both upper and lower intake gaskets. I would think it would show what cylinder if compression is bad in only one. I would test, more for piece of mind to know they are all up to specks

 

Thanks Craby. I got the lower intake installed last night when I got home from work. This weekend I will finish reassembling it. I am 50 and a little confused that people keep telling me to check compression on the cylinders. I used to have a jeep liberty that cylinder 3 lost compression because the valve seat fell out of it but it gave me a different CE light. It was a misfire on that cylinder. If there was no compression, in a cylinder, I should be getting a misfire code for a particular cylinder instead of the random misfire code shouldnt I?

 

yah its just something I would do, mostly to insure that's not an issue that could be part of the problem.

 

When the system says it’s a cylinder 1 miss. All it really knows is that the crank sensor did not pick up the engine RPM as it was expected to see. Let say you are idling the computer is expecting a level RPM +/- some degrees of rotation. What the crank sensor show is that the engine is seeing 3.4 milli seconds between sensor triggers. For some reason it takes 3.5 milli second at one point in the rotation. The PCM then looks at what is firing at that same time. If it happens enough just in that one cylinder it will set as the misfire code. But if there is anything that throws off the rhythm or adds to the PCM confusion it sets a random misfire.

In the case of a blown head gasket it could blow between two cylinders. Depending on how this effects vacuum you could see some misfires in other cylinders like a stumble. There is a chance it could set both cylinders as misfire or it could just show a random. Leaking lower intakes almost always show as random. My guess the coolant get pulled into different cylinders depending on which one is close by and on the intake stroke.

With the right scan tool you can look at the miss fire count. The system will start counting as soon as it starts. What may seem random to the PCM could be obvious to us. Also looking at where the misfires are the highest can help figure out what is going on. Are the highest number next to each other? Are they near a possible vacuum leak, where are they on the fuel rail. If the count number truly looks random that would indicate a system problem, fuel pressure, MAF, ICM or crank sensor.

Of course all of this assumes the cranks sensor is working as it should. I just had to replace the crank sensor in my Dodge ram. It started as random misfires, I cleared the code and it came back in a few days but this time it was a crank sensor failure. The truck did go from a slight miss to a bucking. When I looked at the sensor there was oil leaking through the center of the sensor into the harness connector. I have never seen that on one of my chevys.

I hope that helps