Hello all, this is my first post and I know this topic has been covered a ton of times. I am completely lost with this misfire and have battling it for 2 years now. I have a 2002 Chevy Silverado 2500 crew cab 4x4 with a Vortec 6.0. Truck is from the northeast and has 160,xxx miles on it. It currently has a p0300 code and the CEL flashes only above 2k rpms. My scanner does show cylinders 2 and 3 with over 10k history misfires. Live data shows cylinder 2 and 3 misfire when rpms are brought higher. While driving you cant feel the misfire until I start to tow a trailer.

Parts Replaced/ Diagnosis Done
-Spark plugs, wires, coil packs
- All four o2 sensors
-Camshaft sensor
-Crankshaft sensor
-Valley cover gasket
-Knock sensor and harness
-Intake manifold gasket
-PCV valve and hose
-Fuel injection pressure regulator
-Fuel pump
-New headers
-Swapped injectors with other cylinders(No Change)
-Check ground on wire harness for coil packs(Tested w/ volt meter, Tested Good)
-Smoke tested Intake(No leaks)
-Fuel pressure reading 60PSI
-Crankshaft variation relearn

My only other thoughts are to replace the MAF or do the
Crankshaft variation relearn but I am at a complete loss here. Any help would be greatly appreciated! Thank you!

 

Note*
Cylinder compression test(#1-179psi,#2-180psi,#3-172psi,#4-170psi, #5-175psi,#6-175psi,#7-165psi and #8-181psi)

 

If you did not use ACDelco 41-962 spark plugs, that could be your problem. These engines do not like any other spark plug. Also, the ACDelco 41-962 plugs come pre-gapped from the factory and do not require re-gapping, Attempting to measure or change the gap can damage the platinum coating resulting in premature spark plug failure.

Also, if you purchased the spark plugs from Amazon or ebay, the chances of your getting counterfeit spark plugs is almost 100%. Especially if you got them for a fantastic price. I'm all for saving money, so I purchase parts from rockauto.com which uses the same warehouses as the local brick and mortar auto part stores use.

What brands and part numbers of the ignition coils, spark plug wires, engine sensors, etc. did you install? All parts are not created equally! I am all for using quality aftermarket parts when they are available, and if not, then I'll use OEM. Quality aftermarket brands for engine control parts (sensors, ignition coils, etc.) are Delphi, Standard Motor Parts (non T series), NAPA Echlin, BWD (non P series), Denso).

If you did not perform the CASE relearn after replacing the crankshaft position sensor, then you will need to find a shop with a dealer level bi-directional code reader/live data scanner that can write the new crankshaft and camshaft position variances to the EPROM memory in the ECM.

If none of the "easy stuff" corrects the misfires, then you will need to look at the valves and valve springs on those cylinders. There could be a weak valve spring or a burned valve, or something else.

Good Luck!

 

Thank you for response! I installed acdelco 6 spark plugs but just ordered the ones you suggested. All the other parts were purchased from RockAuto and are acdelco or Delphi parts. I brought it to a shop yesterday to try to do the relearn again but the while it was at WOT, the fuel cut off would not occur. I read online that could be caused by not holding the brake?? I’m not sure but that is also a concern of mine. When I go to change the spark plugs, I’ll perform a leak down test and see what the results are. Thank you!

 

OK on the shop doing a CASE relearn. As to the WOT fuel cut off and the not holding the brake down I cannot comment on.

Roger on ordering the correct plugs and then having gotten ACDelco or Delphi parts from rockauto.com

Good luck and I hope the new plugs correct the situation.