8 months later the car seems to runs fine. I've put about 10K miles on it since the rebuild. I had to return to the shop once for an apparent oil pump failure.

The only issues now are the rough running V4/afm mode and an occasional cloud of smoke (oil) on cold starts after a couple days of sitting.

The engine runs smoothly on V8 Mode in D or when manually selecting a gear... But when cruising in D and it decides to go into V4/afm mode is when a prominent harmonic vibration introduces itself.
Soon I will look more into disabling the AFM as I believe that is where my problems originate.

I suspected that.

I had the engine rebuilt this last July. Chevy dealer diagnostics reported a collapsed lifter and quoted $7k for a new engine instead of isolating and fixing the problem.
They did not admit it to me at the time, but turns out they had a service bulletin saying to replace my engine as a unit instead of repairing it.

I decided to have an engine shop familiar with LS derivative engines rebuild it for me instead.

The shop put a new cam in it and said the original cam had excessive wear. I later told this to my local GM dealer.
Dealer said that "it is almost impossible to cause damage to the cam in this engine [the 6.0 in all hybrids]. Whoever you took it to must not have known what the problem was."

continued...

Hello Hillbilly,

I read one of your comments from November about disabling the AFM/cylinder deactivation on the hybrid tahoe/yukon, etc.

"There is a 5-Way plug way in the back of the engine not too far from oil pressure sender. If you un-plug it. No AFM. There will be codes and a CEL."

My engine runs incredibly rough on V4/afm mode. Almost certain I have the oil problem leading to dirty plugs... I want to disable it.

Is there another knowledge I should take with me before I go search for the 5 way plug and disconnect it?

Hi Hillbilly,

I've searched several threads and you seem to be very knowledgeable regarding the GM Hybrids. I have a 2008 GMC Yukon Hybrid with 98K miles that intermittently stalls at idle. It has kicked several hybrid codes along with the p0420 cat code. We pulled the hybrid battery, disconnected and tested each module individually and they all tested around 8.2v, which I believe is good. There is a TSB for broken or crimped wires and some suggest the control module as a fix on the tech lines, but I thought I'd check with you before throwing parts at it. Should I take this thing to GM or can it be diagnosed by my independent?

Man you have wrote or commented on about every issue I have had. My 2008 tahoe jerks and lunges when switching from hybrid to gas, it sometime revs up at a stop to 2000 rpms for no reason, and now the oil pressure has began to drop slowly (oil pressure sensor screen I think) I am in north Alabama by Huntsville and nobody wants to touch this thing. Where are you located because I would drive a good bit to get someone like you to work on this monster for me.

Hey there HH,

I don't know if you saw my post regarding my Hybrid Tahoe on Sunday. Could a misfiring cylinder wreck havoc on my hybrid system?

Thanks for any help you can send my way...