my 2005 w/ 195k miles on it has been making quite a bit of timing chain noise for the last few months. I was positive I needed to do some work on it but was dreading all the labor to get it done.
a few days ago, on the drive home from work, the engine starting having some real issues at idle and was stumbling on acceleration. I was worried I had a major timing issue (skipped tooth and bent valve maybe?) and decided it was now or never to open up the case and investigate the timing chain.
The tensioner shoes on the secondary chains were completely worn down. Those chains were riding on the metal plunger of the tensioners.
The main tensioner lever arm was also missing some plastic (probably down in the oil pan now) and the main chain was rubbing against some metal on that arm also. That's probably where all my noise was coming from at startup.
Probably the most interesting part of it all was I was missing a tiny o-ring that seals an oil passage port that affects the variable valve timing. Our VQ engines use high-pressure oil to change the timing on the valves (and also the lift duration). I think the oil was squirting out into the main timing case and not fully pressurizing the cam, and thus not causing the VVT to work as well as it could.
Anyway - got everything is back together and the truck fired right up. I was really happy and the timing looks to be exactly right (was nervous about that part). Drove it around the block and the engine starts running rough and stumbling again - crap!
Finally threw a code - p0304 which is a misfire on cylinder 4. Ended up being an ignition coil boot, the spark was getting out of the boot and grounding to the engine. $10 later at the parts store and now the truck is totally amazing.
way more power than ever before, and over the last 2 days, I'm seeing another 2mpg on average. super quiet at startup/idle, butter-smooth on acceleration, and if you really give it some gas I can feel the VVT kick at ~ 3500rpm as the truck pulls.
I'll try to get some pictures posted of the tensioner shoes - the wear was impressive.