Sounded like a collapsed lifter but all rockers are snug

[torquemeister]

2007 suburban 5.3 with AFM. First it threw P0308, then P0300, and it goes into "limp mode" with the service stabilitrak message. It ridles/uns really rough with a lot of vibration, like it could die at any second. The clear ticking sound that gets even more obvious as RPMs increase. I was just assuming it was at least one collapsed lifter, possibly more. Last night I took both valve covers off and none of the rockers move freely. Could it still be a collapsed lifter if all 16 rockers are tight? Or is there a different most likely cause that fits these symptoms?

I'm guessing the next step is to turn the engine over a few times to see if all 16 valves are moving? If so, what is the easiest way to do this? Turn the key like I'm trying to start it or will that mess something up?

Thanks,
-Chris

[swathdiver]

Yes!  Use a breaker bar to turn the engine over at the balancer bolt.  If too hard to move, pull the spark plugs.

[newdude]

P0308 isn't an active lifter if you are thinking an active one failed.

 

If its a hard miss on 8, you can check the movement but you might want to be ready to pull the head and check the cam because its likely the lifter spun.  

[torquemeister]

My initial troubleshooting was based on cylinder 8 being the initial issue, but the P0300 set pretty quickly after the P0308.  I bought an inexpensive scanner that gave live misfires by cylinder and it pointed to multiple cylinders.  It's been a while since I did it but I remember cylinders 4,6 and perhaps 7 having the most misfires.  I had pretty much convinced myself it was a collapsed lifter and parked it for about a year, so some of the details are fuzzy.

[dna9656]

So far as your ticking lifter goes find my previous posts on Oil pick up tube O ring replacement. I didn't have a AFM engine. I had an 06 5.3. You obviously got more problems than a cavitating oil pump.

[torquemeister]

I finally got to work on this again today. Here's what I did:

1. wired up a push button starter from the starter solenoid to watch while turning the engine over. All 16 valves go up and down and look like what I would assume is normal.
2. removed all 8 spark plugs. #8 is completely black at the tip but does not look wet/oily.
3. compression test on all cylinders with the plugs out and with the valve covers still open.

1 = 180 2 = 210
3 = 220 4 = 170
5 = 220 6 = 180
7 = 180 8 = 0 (ZERO, never moves the needle on the gauge)

The valve springs for #8 don't look broken. So this project has gone from me assuming I was doing lifters and maybe the camshaft to something entirely different. Question is, what is my next step and what is the common/likely cause or causes??

Thanks,
-Chris

[CamGTP]

Could always take the rockers off cylinder 8 to see if the valve springs are indeed good, even compression test it that way too.

 

Next would probably be to put a bore scope down the cylinder to check the piston out. If that looks okay on top, then it's either a headgasket issue or the piston rings have failed, those are just my guesses.

[richard wysong]

Maybe burnt valve? if you're in there with the borescope take a look with the valves open, also could be broken valve seat, that would explain the noise too

[richard wysong]

unless it's a valve spring problem you are gonna have to pull the head at a minimum