2002 Chevy Silverado 5.3 code po300

Question

I have a 2002 Chevy Silverado 5.3 I have changed all 4 o2 sensors, plugs, wires, fuel filter, air filter, and still I get a P0300 where do I go from here.

Answer 1

P0300 Random misfire

Doing the sparkplugs , sparkplug wires, fuel filter , and airfilter, this is all good there are more area to test for Random misfire condition here is just 2 more possibility that goes unnoticed until it is very apparent

 Here is a fuel pressure regulator that caused a random misfire , this would be a easy one as it would code a P0172 or a P0175, On this vehicle the owner complained of hard start up at cold start , until the vehicle reached operating temperature, To determine if this is the cause at idle pull the vacuum hose off if there is a trace of fuel the regulator would be the cause of the misfire condition

 

 Here a catalytic convertor this one plugged due to prolong , the vehicle misfired at idle and no power during acceleration,