Another Engine Misfire (P0300) Question

[sc_customs]

I'm having a problem with the P0300 Engine Misfire Detected when the truck is at a constant RPM above 2000. Normal driving doesn't seem to trigger the code. Anyone had a similar problem or know what might be the fix?

I've tried new plugs, wires, injector cleaner, and the coil packs seem to be fine. The misfire isn't even noticeable. I just get the flashing SES light out of nowhere.

Any advice would be helpful. Thanks.

[sc_customs]

I was reading in my Haynes manual in the troubleshooting section about the engine misfiring and it says that one of the causes could be faulty emissions components, which might explain why I am also getting an error P0442 Evaporative Emission Control System, Small Leak Detected.

I've read the "Gas Cap Code" thread and it vaguely explains that this code is a pain in the you know what to diagnose.

I guess my next question would be if anyone has came across a similar problem like this and where to begin looking (besides hoses).

[maxwedge]

The p0442 will not cause the misfire code, is the miss something you can feel? Lots of mods there, any other pending or history codes?

[sc_customs]

Nope. Can't feel the misfire at all. There isn't even a difference in performance. Do you think one or more of my mods might be the cause?

As far as other codes are concerned. This is the only code that's ever appeared since the motor was dropped in, besides the P0442

[BlenderWizard]

I know that with my Nelson tune, the PCM kept spitting out the "random/multiple misfire detected" code. I had Alan turn down the misfire count, and it's gone.

I think adjusting timing tables (which causes the ignition system to fire at different than normal times) makes the PCM think the engine is misfiring sometimes.

[maxwedge]

Originally Posted by BlenderWizard

I know that with my Nelson tune, the PCM kept spitting out the "random/multiple misfire detected" code. I had Alan turn down the misfire count, and it's gone.

I think adjusting timing tables (which causes the ignition system to fire at different than normal times) makes the PCM think the engine is misfiring sometimes.

Agreed, that makes sense once the factory programming has been altered.

[sc_customs]

Well the only thing the handheld changed was the shift points and firmness. Could this be causing the misfire? Perhaps I should return the PCM to stock and see if conditions improve?

[BlenderWizard]

Originally Posted by sc_customs

Well the only thing the handheld changed was the shift points and firmness. Could this be causing the misfire? Perhaps I should return the PCM to stock and see if conditions improve?

You're sure the handheld did nothing for your timing?

[sc_customs]

There are no options in the tuner that modify the timing, unless it does it automatically to change the points and firmness.

The only modifications the tuner can do is change the shift points, shift firmness, rev limiter, speedo calibration for aftermarket wheels, and clear the DTC's.