Misfire p300, p171, p174
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.
A dirty or bad MAF (Mass Air Flow) sensor can cause the P0171 & P0174 codes together. The P0300 code should be ignored. It's most likely being triggered by the two lean condition codes. If you have one of those aftermarket cold air intake system air filter set ups the MAF is highly suspect. The oil used on the air filter contaminates the MAF! Another cause for the two lean codes could be a stuck open PCV valve. HTH. -Jim
Ok will have that checked. Don't have a after market cold air intake. It might still be the mass air flow
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.
With both codes together the MAF is definitely suspect since you don't have a vacuum leak. If you don't know when the PCV valve was last changed, replace it. They're very cheap. HTH. -Jim
Pcv valve and mass air flow sensor both checked and not the problem. Still miss fire and lean codes
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