Mystery Misfire codes?

[Mr. P.]

I have a truck with a random mystery P0300 (general misfire) code. The truck is a crewcab 2004 GMC Sierra, it originally had a 4.8L and we swapped/upgraded a fresh crate LQ9 6.0L from Scoggin-Dickey. Truck runs and drives *fantastic* but randomly it will flash the SES light with a P0300, it will do this once every 1-14 days (the truck is driven daily). Other than that, truck gets great mileage and power, we believe this is a phantom code as there are no other DTC codes or PCM history to support it, we've walked completely through the ignition twice ???

SO HERE'S MY Q - is it possible that this engine swap requires a CASE relearn? Has anyone else run into a situation of a phantom misfire code?

Mr. P. :)

[ScarabEpic22]

If you used a different PCM than what originally came with the motor then yes, you need a CASE. Id do it anyway, only takes a few mins and it will eliminate one possible cause.

[Chevy366]

I have a truck with a random mystery P0300 (general misfire) code. The truck is a crewcab 2004 GMC Sierra, it originally had a 4.8L and we swapped/upgraded a fresh crate LQ9 6.0L from Scoggin-Dickey. Truck runs and drives *fantastic* but randomly it will flash the SES light with a P0300, it will do this once every 1-14 days (the truck is driven daily). Other than that, truck gets great mileage and power, we believe this is a phantom code as there are no other DTC codes or PCM history to support it, we've walked completely through the ignition twice ???

SO HERE'S MY Q - is it possible that this engine swap requires a CASE relearn? Has anyone else run into a situation of a phantom misfire code?

Mr. P. :)

I noticed after the cam install that I will get a misfire code if idle is to low and it lopes , or I ran the battery down and before it charged back to correct voltage I got the P0300 code at idle .

[chevy052500hd]

Do a case relearn on the pcm, I swaped a crank sensor in my s10 didn't do a case and it would show that code. Did a case went away.

[Mr. P.]

Thanks gents, will do the CASE relearn and report back later on the result.

Mr. P. :)