[Jeiselr4]

I have a straight piped 2011 Nissan Altima, i don’t believe anything else was done to the car. Has an isolated misfire on cylinders 2 and 3, I switched the ignition coils, spark plugs and put in a new valve cover and gasket, ran a compression test and came back perfect, codes read a P0300 for...

 

[VStar650CL]

Poke a flashlight down the spark plugs holes and see if the crowns on 2-3 are shinier than 1-4. If so, it's likely a small head gasket leak into the cooling jacket. Also, because the sleeves on the QR25 are siamese, it's possible to get a leak between two adjacent cylinders without the cooling or oil jackets being involved. Tiny leaks of either kind may not cause a substantial compression loss, but enough to cause a come-and-go misfire.

 

[Jeiselr4]

Uh what? I didn’t understand any of that

 

[VStar650CL]

I don't think I can make it any clearer. If you don't understand engine terminology then the help anyone can give you will be fairly limited.

 

[Jeiselr4]

not what I meant, I doubt it’s a gasket leak bc I already replaced the valve cover and gasket

 

[VStar650CL]

The valve cover gasket and head gasket are completely different things. If you don't understand something as elementary as that, you should let a professional look at it.