I was wondering if anyone has run into codes p0300 & p0174. I only get them under a heavier load. They don’t show up under normal driving they show up after it downshifts like when I pass someone the CEL flashes then runs rough. If I shut it off and restart it , all is ok. I smoked the vacuum system from the pcv hose by the valve cover towards the intake and no leaks, I even pulled the filter change reminder out to ensure smoke was all the way there but no obvious leaks. I have 58lbs of fuel pressure at idle and the same at 2000 rpm. I pulled and flushed the injectors and physically energized them to clean them. I cleaned the MAF sensor as well with no change. It is only bank 2 that’s lean. Maybe oxygen sensors? Any help would be greatly appreciated. BTW it is a 2004 H2 with 128k. Thank you for any and all help

 

Gas in the tank?
(((Using E85 Fuels in Non-Compatible Vehicles)))
Fueling non–E85 designated vehicles with E85, or with fuels where the concentration of ethanol exceeds the Owner Manual indicated maximum of 10% or 15%,
may result in one or more of the following:
• Lean driveability concerns such as hesitation, sag and/or possible stalling.
• MIL illumination due to the setting of a diagnostic trouble code (DTC).
• Fuel Trim DTC P0171 and/or P0174 may set.
• Misfire DTC P0300 may set.
• Heated oxygen sensor (HO2S) or oxygen sensor (O2S) DTCs may set.
• A Traction Control, Stability System or ABS lamp may illuminate or a message may display in the DIC (if equipped).
• Harsh and/or firm transmission shifts due to the transmission defaulting to maximum line pressure.
• Fuel system component corrosion and/or engine mechanical component degradation.

 

Thank you something to consider but I don’t recall using e85 or heavily concentrated ethanol gases but great thing to know

 

Anything I can add to the gas to be sure to counteract that?

 

Intake manifold gasket leak could cause that. Small enough to not really affect things much but under heavy load starts pulling in some extra air on the one side. That is a common issue and GM even had a TSB about it on the plastic truck intakes. Recommended to insure manifold ports are still flat with a straight edge and if not to replace the intake, if not warped just replace the gaskets. I have personally had this issue and sure enough I was able to see a couple of tiny spots where the stock gaskets were no longer fully contacting the head on the passenger side.

Might very well not be the issue though and I'd suggest that if you are going to pull the manifold that while you are at it go ahead and replace the knock sensors and knock sensor harness and maybe the oil pressure sensor since it is easy to access with the intake off.

Other might have some ideas on other things to check as well.

 

Have you done any work to the truck lately, something like changing any part of the rotating assembly of the engine or transmission? Have you changed the crank sensor or the cam sensor recently?

Its a little odd that your getting both a rich and lean indication from the PCM.

I would take a look at the pressure in the Bank 2 exhaust pipe between the engine and the CAT, a partial plugged CAT can cause some strange issues.

 

Try more OCTANE, run a tank and post the results.Gasoline explained

 

Will try anything and thank you all. And to answer a question, this started out of the blue no other work was being done to cause this.