04' Sierra P0300

[gbayfisher]

Hi guys,

I have a 2004 gmc sierra 2500 LD, 6L, 4x4 50,000 miles. Been setting a random misfire code for a couple months now, and I am trying to narrow it down.

What I have scanned so far:

-p0300, only code ever pulled thus far.

 

Seems to idle very well, has an ever so-slight cold start "stutter" or slight shake if i can even call it that.

I have owned 4 6L'ers before and they all seemed to have had the same cold start/ idle like this one, so i don't think it is a problem.

I have never felt any type of stutter indicating a miss at start up or cruising speed. slight ping at high rpm (4-5500) on very humid/hot days. I have set the code at any rpm, in hot and cool weather.

my friends scanner pull this misfire history:

Cyl

1. -13,422

2. -13

3. -11

4. -25

5. -39,363

6. -5,946

7. -9

8. -54,225

 

That's a pretty wide spread of misfires. Every cylinder has missed!

Upon resetting the code, it could go 1-4 days without setting it again, the longest between codes is 6 days, which came after treating the fuel tank with seafoam and injector cleaner, and also allowed seafoam to be injested through the throttle body to try and clean any carbon that may have built up over time. I have also cleaned the MAF and the air filter is new (5k ago).

I have checked for intake air leaks (hot and cold) and cannot find any at all, doesn't seem to have any exhaust leaks that i can hear clearly, maybe a little raspy like all my other 6l's.

Where should i go next? the symptons would indicate a air leak to me? Could I be missing an intake leak?