CEL flashing and P0307 code

[Aerovette]

2015 GMC Sierra Denali 5.3 4WD with 93k miles

 

I've only owned the truck about a month. It has always been well maintained (I know the owner indirectly). Three days ago, I was entering the highway and acceleration semi-aggressively as it was a short runway. The CEL started flashing and did so about 5 times and never again during my hour long drive home. The trip sees a wide range of speed acceleration, V8 and V4 conditions. Speeds between 25 and 80. It didn't do it again until today. Today it flashed longer and went away. The first time I felt no performance change. This time I seemed to feel a stumble/sputter, but accelerating harder made it go away. I stopped and read the codes at the parts store and got the P0307. Initial research paints a scary picture. I "hope" it is just a wire, plug, coil, but I'm not typically that lucky. There is no tapping or ticking and both times it was in the same exact spot of roadway and same conditions. I just took it for a ride after sitting several hours and I can't duplicate the issue. No CEL regardless of acceleration and no stumble at all. Would a failing lifter be intermittent? Any ideas? What I plan to do is swap wires, check #7 plug, and see what happens. Problem is, I won't know if I had any impact if I can't repeat the issue. Note: It is due for an oil change. Any additive (that actually works) I can put in to free up a part that may be sticking? I'm all ears on the issue. I hate to think that I have to tear an engine apart on a truck I just bought. Before anything gets worse, would programming the AFM out help at this point or am I already to late?

 

Thank you

[HeySkippyDog]

You don't have to program it out, you can buy a module from Range Technologies and just plug it into your OBD port and boom, V8 all the time.

That said, you may be too late.

Try a can of GDI engine cleaner and spray it into the intake per the instructions on the can.

Change the oil and see what happens.

If you end up in the clear, you'll want to drop the V4 and probably run an oil catch can on your PCV. Continue the GDI cleaner every oil change.

Good luck.

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[Aerovette]

3 minutes ago, HeySkippyDog said:

You don't have to program it out, you can buy a module from Range Technologies and just plug it into your OBD port and boom, V8 all the time.

That said, you may be too late.

Try a can of GDI engine cleaner and spray it into the intake per the instructions on the can.

Change the oil and see what happens.

If you end up in the clear, you'll want to drop the V4 and probably run an oil catch can on your PCV. Continue the GDI cleaner every oil change.

Good luck.

Sent from my SM-J810F using Tapatalk
 

Well crap. That's less than encouraging.

[HeySkippyDog]

Hey, it could just need a little cleaner sprayed in. No way to know for sure.

Are the miles on the car mostly highway or city crawling?

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[Aerovette]

I believe the miles are a mix of both. I had to remove the air inlet to replace the alternator (that it didn't actually need, but that's another story) and I did notice the butterfly was Tarnished/tinted/dirty. Maybe I'll get lucky with a cleaner through the intake. I had my last truck 17 years and knew everything about it. This one is all new to me so I'm lost.

[HeySkippyDog]

I believe the miles are a mix of both. I had to remove the air inlet to replace the alternator (that it didn't actually need, but that's another story) and I did notice the butterfly was Tarnished/tinted/dirty. Maybe I'll get lucky with a cleaner through the intake. I had my last truck 17 years and new everything about it. This one is all new to me so I'm lost.

I know, I'm just as lost too and this is my 2nd one of this generation. A lot of it I don't understand. I know the old stuff, but these are difficult.

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[CamGTP]

I'd honestly just change all the plugs if you don't know if they've ever been done.

 

Not saying a wire can't go bad but I've seen more actual plug issues than wire issues. Hell, we used to save all the old wires from junkyards or vehicles we did service work on. Throw them in a box for when we by accident damaged a wire doing something else.