P0300 Hummer - H2 2003

Question

I had an O2 sensor changed then check engine light came on now I have 3 codes 2 O2 sensor codes and a P300 code. It hesitates on occasion when first starting unless I let it run for a few minutes, when it hesitates check engine light flashes then stops flashing then runs fine. Sometimes the check engine light will go off on its own then come back on a couple days later with no issues. I had a complete fuel injection cleaning done and also put two complete fuel injector cleaners in fuel line but hasn't helped. Any ideas what this could be?

Answer 1

P0300 Random misfire

CK ENG LT flashing this is usually related to the ignition system. The ignition wire can short to ground intermittently causing the misfire to occur, the solution for this may be replacing the sparkplug wires , there is also the possibilty of the fuel pressure regulator leaking fuel into the intake. the H2 is equipt with a fuel pressure regulator. a leaking pressure regulator can also be one of the cause

 This is a fuel pressure regulator that caused a P0300, by pulling out the vacuum line , evidence of fuel leak from the diapghram proved the regulator was faulty,

Here is a ignition wire that can leak secondary voltage and cause a misfire,but in order to cause a P0300 two or more wire can be faulty.