P0307 and more.

Aerovette · October 17, 2021

2015 Sierra Denali 120006 miles. I bought this used and occasionally I would get a P0307 code. I'd erase it and it would drive for months with no issue. Last night I went to dinner..' all good. I start the truck to leave and as I pull out I get a stabilitrak light and a flashing CEL. Reduced power and bad idle.

Today I:

Disconnected the battery for a couple hours hoping for a miracle "reset" no luck.

Swapped 1 and 7 coil, plug, and wire. No luck

Observations:

NO lifter tapping

#7 plug was oily

When no code is present, oil pressure is about 30.

When stabilitrak light comes on, oil pressure increases to just over 40 and I can hear some sort of sound like air flowing or vacuum or something.

When I clear the code, the sound goes away and the oil pressure goes back to 30.

CEL comes on long after the Stabilitrak has been on a while. (minute or more)

Only ONCE after I first swapped the plug, coil and wire, I got a cold rough idle code P050D

V4/AFM does not engage

CamGTP · October 18, 2021

So you are only getting a P0307 currently right?

It's likely to be a lifter issue with the AFM if there are no other codes for something like the injector.

You can pop the drivers side valve cover off and crank the engine over with fuel system disabled to see if all the rocker arms are moving.

TJay74 · December 16, 2021

P050D is the code that triggers when an injector is failing during cold start. There is a service process to determine which injector it is that is failing. The increase in oil pressure is part of the reduced power mode as part of the fail safe for the engine.

If swapping the plug, coil and coil wire didnt change the position it leaves either the injector is failing or the AFM lifter has failed on that cylinder. While the injector is not hard to R&R it does require pulling the intake manifold and the injector rail. Per the service manual you will need both of the hard fuel pipes to be replaced as they are listed as 1-time use, I have reused them in the past with no issues as well. If you buy a new GM injector you will need the injector info printed on the injector to determine which injector you need as at one time there were 3 or 4 injectors to chose. The brand new injector comes with the teflon seals already installed.