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?

Asked by Nov 25, 2012 at 08:10 PM about the 2007 Chevrolet Silverado 1500 LS Crew Cab SB

Question type: Maintenance & Repair

fuel pressure good , plugs , MAF,& wires good, coil good, purge solenoids good, ready to call up dealership.

3 Answers

33,395

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.

33,395

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

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