I was on my way to work and almost there when the knocking or tapping noise started under the hood. Knew instantly this meant an expensive and urgent repair job. Took it to the shop and they diagnosed it as a stuck lifter (not to my surprise). It was in the shop for a week and a half since the lifters on the Active Fuel Management (AFM) engine needed to be ordered and the heads machined. Apparently this is a common issue with the AFM engines and I was lucky to make it to 167,000 miles before it happened to me. Such a costly repair for a recurring problem in these engines! Beware, if you make it to 100k miles, this problem is any day on the horizon! I like the reliability of the GM 5.3L V8 engines, but the AFM is terrible. I'll never buy another AFM engine again.

Bought 08 Sierra new off lot w/8 miles. changed oil myself @ 3000-5000 miles. My baby. @ 193K miles, oil pressure suddenly went ot ZERO. Lifters on odd number bank 1,3, 5, 7 were raising hell. changed oil pressure sensor and valve lifter filter underneath. got good O/P but engine missing terribly. AFM system totally failed. Per several mechanics including good friend, confirmed total top end rebuild including camshaft. Parts cost $1500 for cam, lifters, pushrods, intake gaskets, exhaust gaskets, exhaust donuts, coolant, oil. Labor cost $1000 more. Great engine until sudden collapse. GM F____ed everyone on these engines which they still make and put in vehicles. Ford, Dodge, Toyota, Nissan etc for me next time. I've been a GM nut for 47 years now but it's over. My mechanic drives Fords because he knows about the New Gen GM engine design flaws. Work your ass off to keep an engine in excellent maintenance and it still f*cks you. No more for me.

Update from Jun 21, 2017: After getting the head off on odd bank for lifter replacement, found # 5 AFM intake valve stuck all the way open and big dent in top of piston. Reason, AFM lifter instead of collapsing as in normal failure, this one stuck open causing piston to hit it. In the perfect GM world, the pushrod would bend as it's supposed to be the weakest link. NOOOOOOO, GM put the best pushrods ever made in this engine. The lifter failure caused a bent piston rod which cocked the piston itself against the cylinder wall. Had to replace entire engine. Plan to sell it when back running and get new Nissan, Ford, Dodge or Toyota. Pay $32K for a new truck in 2008, change oil 3000 - 5000 miles, and replace engine at 193K miles. These LS engines should be good for 350 - 400K with good maintenance as in my case. I've got a real sour taste in my mouth about GM. Beware.

I was driving and heard a slight ticking noise and took it to the dealer. They couldn't identify the problem and told me to bring it back if gotten worse. Well I didn't have to wait long, I broke down due to collapse lifters. Luckily I was still under warranty, but reading up on the 5.3 AFM motors I noticed I'm not the only one who's had this problem. I really think GM needs to fix this problem and stop ignoring it. I will make this my last GM vehicle if this is not fixed. I've been with GM for over 30yrs and this is unacceptable.