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Troublesome Random Engine Misfire


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I have a 2001 GMC Sierra 2500 SLE 4 WD Extended cab with the V8 6.0L gasoline engine. 

110,000 miles

There is a P03000 Random Engine Misfire code that shows up when under load (typically 2500 RPM or higher); check engine light flashes when under load, but will turn off when RPM goes above 3500 or below 2500 for more than a few seconds. Check engine light stops flashing when not under load, but still shows as pending or set on scan tool.

After some initial obvious repairs (detailed below) the only symptoms I see are a very slight sputter at idle. Under load I do not notice hesitation, loss of power, sputtering or misfire. The truck has good power and acceleration.

Here are the troubleshooting steps and repairs I've completed:

  1. Purchased used; had the engine light (p03000) and found the passenger side header was cracked. Replaced the header and all spark plugs (since I damaged one while replacing the header). I also removed and visually inspected passenger side fuel injectors, no obvious wear or damage or clogs. Ran the truck for a few days and code returned immediately and did not reset after several driving cycles.
  2. Checked for vacuum leaks with carb cleaner sprayed on all vacuum hoses, intake, and manifold gasket. No surging or change in idle.
  3. Replaced fuel filter and used fuel injector cleaner for two tanks of gas. No change in condition.
  4. Tested fuel pressure. Reading was about 10 psi low, so replaced fuel pump. No change, though it feels as if there is more power on fast acceleration.

I am including links to images from my Blue Driver scan tool. Voltage on bank 2 sensor 2 seems to be non-responsive. (scan images - first is at warmed up at idle; second is at 2500 RPM, third is at 3500 RPM; fourth is code reading)

2 Answers

I don't think your bluedriver will be able to access the misfire monitor for anything under a 2005 model year but you can try switching to Mode 6 to see if it can.

Your best bet is to find someone with a decent scanner that can access the misfire monitor on your 2001 GMC and see which cylinders are acting up. If they're all on one cylinder bank that would be a huge clue. Or maybe you just have a couple of weak ignition coils which are acting up under load.

Aside from that you can look at your fuel trims to see if one of the cylinder banks is running lean or rich for a clue. 





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