2007 Tahoe Misfire Losing Communication P0300-00, P0575-00, U0073-00, U0100-00,

Good evening guys,
2007 Tahoe, 5.3, ~200k
I am getting P0300-00, P0575-00, U0073-00, U0100-00, C0561-71. Symptoms are strange. If I start it and let it warm up, I can drive it at very low throttle for as long as I want. But if you have to step on it very hard, the engine light starts flashing, the stabilitrack light comes on, and there is a significant power loss. Looking at misfire info, cylinder 7 is almost always dead. Sometimes another cylinder too. Most often, cylinder 2, but sometimes cylinder 8. After it starts acting up, sometimes, but not always, the doors will lock a few times on their own. Sometimes the speedometer will twitch.

I swapped the fuel injector, coil, plug wire, and plug on cylinder 7. I have cleaned all the grounds on the engine and in the engine compartment, and the one under the drivers door. I have pulled the connectors on the ECM, TCM, and BCM. All the pins are in good shape. I have not stripped all the tape or loom off the wiring harnesses, but they look to be in good shape. The fuse box connectors are all in good shape. Nothing has made any difference. I have been working on this for a long time.

Brief history, We bought it a five months ago. It would rarely, like once a month or so, for a short time have a dead miss that would clear up pretty quickly on it's own. It was getting more frequent, but still not intolerable. Then we ran it low on oil, and one of the AFM lifters collapsed. I changed the lifter and it ran ok for a few weeks with the miss becoming more frequent. Then the lines on the fuel pump sending unit rusted out. I replaced that, and it ran ok for just a couple days, and now the miss has to be addressed. It is essentially undriveable now.

I don't know what to look at next. I can't replicate the problem in the garage. It only shows up under load. Any ideas?

I have an Autel MS906BT, uScope, DVOM, test light, etc.

Thanks in advance for any help, and sorry for the book length post.

Sorry we didn't get back to you sooner, Captain. :blush: Hope we can still help.

To be clear, were the door locks and speedometer symptoms present before the AFM lifter replacement? Or were those new after the repair? Speaking of lifter replacement, did you see any damage to the cam lobes or the lifter rollers while you had it apart?

Since you have a nice scanner, I'm inclined to suggest chasing the misfire first, then see if it circles back around to the U-codes. They may be related? They may not. But the misfire sounds easier to reproduce.

I think fuel trim and O2's at idle, light throttle and during the power loss would be the place to start. It may not lead us very far if the PCM is forcing open loop during the misfire, but it might give us a few clues.

Hi Tyler, thanks for the reply.

The door locks and speedometer issues are very new. After the AFM replacement, but not until a few weeks after the repair. The rollers and the cam lobes looked good. The funny part of it was that the lifter for cylinder 1 collapsed, but cylinder 7 is the one that gives me the most trouble.

I am at work right now, but I will try to look at the fuel trims and O2 tonight.

Thanks for the suggestions.

I hope this is OK for you. If I should have done anything differently, please let me know.

O2 Sensors


Fuel Trims


Freeze Frame Data


The report from the Autel is attached.

I had this same code (C0561-71) along with a P0300 on my 2008 Chevy Avalanche 5.3 and I checked misfire data (on my MS906TS) and the only history was on cyl #7. Which on that motor is known to go bad or get oil soaked. I changed just that spark plug and reset the codes and it has been fine ever since. The misfire could possibly be throwing other codes, I would definitely start there! Not to mention it's probably one of the easier things to attack.