Edmunds Answers



  • aintgonnapay 01/17/10 5:51 am PST

    Had the same problem with Random Misfire code P0300 on a 99 4.3L with 183,000 mi. But mine was idling rough and jerky take-offs seemed to smooth out at hwy speeds but no power under a load. I threw alot of money at every electrical part also, plugs..wires..cap...rotor...EGR valve...Coil...Ignition Module...O2 sensors..New Catalytic Converter. Finally had enough and took it to a shop. they spent 3 hrs tracking down the problem, which alot of these TBI injected rigs are having at high milage the mechanic told me. they tested fuel pressure, spark, sensors,...eveything was fine until he pressurized each individual injector. 3 of them held 60 psi which he told me they shouldnt hold pressure at all. the poppet valves were clogged on all 3 injectors. he said it would be $650.00 to replace them but would try to blow them out with 120 psi and running a detergent thru the system for an hour. thank god it worked, so $307.00 and alot of picking a GM certified mechanic's brain...my high milage truck is cruising down the hwy again. I read alot on the internet about these codes and sensors & what alot of "mechanics" had to say. my advice...? take it to a shop you trust, let them spend 1/2 a day tracking it down and let them do the Deep work. Hope this helped & Good Luck my friend!


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