Looking at a truck for a friend after he said the CEL started flashing and it was missing on and off. It is a 2011 Silverado with the LC9 5.3. 93k miles and only mods are a K&N CAI that has been on since new. Looking at it with my Tech 2 it would only miss when it went into V4 mode on cylinder 5. I know 1,4,6,and 7 are the AFM cylinders so it struck me strange why #5 would be missing. #7 would only start to miss right after it went back into V8 mode for a very short time.Before I noticed that it was related to AFM activation, I swapped the coil, plug, and wire with a different cylinder to rule out an ignition problem. Anyone have any insite on this? I did disable the AFM .

Edit: Truck runs fine now after disabling the AFM.

 

So what happened after swapping around the coils and plugs and wires?

How's it doing with the AFM turned off?

I'm at tech too, one thing I would say is don't get too caught up in the AFM on and off and make sure you don't skip checking your basics. Too many times I've made simple problems complex and circled back to finding it was just a basic issue to start with. It very well could be a complex issue with the AFM, but hard to say from over here. Sorry I haven't experienced the exact issue you're looking at so I don't have anything on it.

But if it still misfires with AFM off, then it sounds like maybe one of the basics is causing issues.. plugs, wires, compression for example.

 

All is good now. No misfires after turning the AFM off. Sorry, I went back and added that. There was no change when I swapped the ignition parts around before I saw it was related to the AFM. I'm not at a dealership anymore. I had a failed lifter come in at under 700 miles on a '09/'10 right before our place was closed down. The internal spring had broken. I even had an '09 bite me once. Higher mileage and misfire on #7. Valve and push rod was bent. Pulled the head, replaced the valve and push rod and pulled all the lifters on the drivers bank and they were all good. Ran good no misfires. Half mile down the road it got me. Ended up replacing all the AFM lifter on the side only as the guy had it already sold. Learned my lesson on that one.

 

Can you just leave the AFM disabled on the truck you're currently working on?

 

Absolutely.

 

Fixed! lol

 

I got bit once, cylinder 5 and 7 fuel injectors wire connectors were swapped. It knocked with it came out AFM mode only. No codes other than misfires when coming out of AFM mode. That one threw me for a loop...

 

Bet that had you chasing **** for a while!

 

Yeah a just a few hours of lost time, worst part is that I marked positions with dissembled, so it came in like that. Makes you question your sanity.