I'm getting P0300,P0174,P0420,and a P0420 codes on my 2007 4.3. Sluggish with no power, engine knocking.What can it be?
fuel pressure good , plugs , MAF,& wires good, coil good, purge solenoids good, ready to call up dealership.
What is the intake manifold vacuum? What is the fuel pressure? Im assuming that the order you wrote the codes down is the same order they came out of the scanner. That would make the multiple random missfire the only present code and the other two a history code. Also low fuel pressure and/or a vacuum leak would cause all three codes and the effects you describe.
checked fuel pressure , showed 60 running, 55 while ignition in on position.
Showed 60 while idling? That's way to high check fuel pressure with the key on engine off then add 18 inches of vacuum to the fuel pressure regulator. Post the results
Sounds like a fuel pressure regulator pull the hose off and see if it's dripping fuel
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