Misfire p300, p171, p174
30

Asked by Help_mysilverado3 Jan 28, 2017 at 10:33 PM about the 2001 Chevrolet Silverado 2500HD LT Extended Cab 4WD

Question type: Maintenance & Repair

Have a 2001 Chevy 2500hd 6.0 Liter 4x4. Truck is running
rough throwing codes p300, p171, p174 which I know is
misfire all cyclinder, and lean code on pre cat oxygen
sensors. Have already replaced plugs with suggested
NGK iridium tip gapped at .40 wires replaced also. Still
nothing. Been to two different shops one in which was a
Chevy dealer. Was told needed two injectors, they
replaced ran ok for a week and back to what it was doing.
Then told needed to just replace the remaining 6 injectors.
Bought a match set of remanfactured ones with warranty
etc. they installed and said runs worse now. Fuel pressure
is good, have great spark in all cyclinders. Intake gasket
no leaks, throttle body cleaned. No vacuum leaks of any
kind. Parts already replaced before everything, fuel pump,
filter, pressure regulator. Since then been to a total of 4
shops and no answers what is going on.

3 Answers
30

Help_mysilverado3 answered 7 years ago

Ok will have that checked. Don't have a after market cold air intake. It might still be the mass air flow

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Help_mysilverado3 answered 7 years ago

AskTrannyMan, yes it was the Chevy dealer that said it ran worse with the other injectors in. Also, for got to add to the write up, truck has 102,000 miles.

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30

Help_mysilverado3 answered 7 years ago

Pcv valve and mass air flow sensor both checked and not the problem. Still miss fire and lean codes

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