I just got my 5.3l Yukon tuned hoping to clear out the codes and figure out why my flashing engine light keeps coming on but no luck. O'2 are firing correctly, new plugs and new wires but I still cant nail this random missfire. the code that we were able to pull was a p0300. I am running tr55's with a .45 gap on them and the truck on stock tune was pushing 26* of timing at wot with ZERO kr. between this and the damm tranny not shifting into the 4th, I would have pulled my hair out if I wasnt bald already my buddy at the dealer with a tech 2 and my tuner couldnt isolate which cylinder was missfiring just kept getting a random.

thanks!

 

It's probably not ignition related at all, it's probably fuel but it might be a vacuum leak. What were the other codes that you cleared?

 

any trans mods? converter stock?

 

Our local tuner checked every code and the only thing popping up was the randomm missfire. I changed plugs and wires, cleaned the maf, checked the cai for oil drips, changed trans fluid and attempted the fuel filter but it was so damm rusted at the nut I just left it alone. Stock converter but I did have the corvette servo installed, and when we checked it over the verter was locking up but wasnt going into 4th. Turns out the 3rd gear apply piston was installed backwards and wouldnt engage 4th. This little mishap caused all of the missfire codes too apparently.