P0300 code

[BarryC]

Good day all,
My H3 has been coding the Dreaded P0300 code! (Random cylinder misfire)
I started with the most obvious and relatively cheapest fix...new plugs.Still coded...so next I replaced the Coil packs,still codes! Only codes when It idles?! Runs perfectly fine..no misses or poor acceleration etc?!! I then cleaned the throttle body as well...still fkng codes ???!!! Doesn't appear to have any vacuum leaks either...and new fuel pump a year ago...so fuel pressure is also good! Any suggestions would be appreciated .

 

[H3Hummer]

Did you try to clear the code with an OBD2 reader? I had the same one , but after replacing my 5 coil sparks and sparks, cleared the code on OBD, it was gone and didn't reappear .

 

[BarryC]

Yes of course. Be senseless not to clear the code
..Lol

 

[Happy Hummer]

What brand of sparky?
What brand of coil?
Did you also remove TB?
Have you dumped in a 20oz. bottle of Tecron ? Great stuff...
Have you swapped in new o.e.m. o.g. injectors?
Have you replaced or at least tighten the intake manifold?

 

[alrock]

Wish I had good recommendations. Mine was the bad outcome (new head) and I had no other symptoms. That said, most are able to resolve that issue without a new head.

 

[08H3]

When I was fighting that it was the intake manifold. Check and make sure all the bolts are tight.