Chevrolet Repair: misfire under a load, hairline cracks, gmc sonoma

Question
QUESTION: i have a 98 gmc sonoma 2.2 it had a misfire p0301 about 3 weeks ago, i replaced the plugs and it ran fine until this week.When i take off from a light or i try and put any kind of load on the engine it starts to buck and back fire in the air box then smooths out,it does that in every gear.i can cruise the freeway without a problem until i downshift to pass.

ANSWER: Hey Andy,

  If it is an ignition missfire it may need ignition wires.  Pull them off of the coil towers and make sure there is no carbon tracking down the tower to ground.  The coils sometimes get hairline cracks in them causing them to arc to ground when damp.  If you get an atomizer spray nozzle (like a windex bottle) and lightly dampen the ignition wires you will quickly see where the arcs are under load.

Wayne


---------- FOLLOW-UP ----------

QUESTION: would an ignition misfire trigger a check engine light because i don't have a light on and there are no codes for a misfire.probably should have told you that the first time sorry.

Answer
Hey,

 Not always.  GM's are a bit aggravating sometimes.  I had a TECH2 on an 2001 Venture a couple of weeks ago and cylinder 3 registered 65,000 miss fires but there was no miss fire code.  Likewise I have seen them run perfectly and set P0300 multiple cylinder miss fires right before my eyes.  It isn't uncommon to see corrections in the software when we reflash to eliminate or enhance missfire diagnostics in the new software update for the PCM.


Wayne