Forum readers,
I'm stumped. My 2015 Chevy Tahoe went to the body shop for 3 weeks to get hail damage repaired and when I picked it up there was a loud ticking sound coming from the engine. I immediately suspected a collapsed lifter and possibly low oil pressure, so I began troubleshooting by checking the oil level. Someone had overfilled it by 2 quarts and drove it 20 miles while at the body shop! (They are saying that they didn't touch the engine during the body work, so it couldn't have been them...) In any case, it looks like the cause of the problem was oil aeration and subsequent loss of oil pressure to the lifters. I used the stethoscope with the engine running and it was clearly coming from the right side, #4 cylinder at the valve cover. I bought the lifter release tool last week because I was fairly certain it would be a collapsed lifter, but after pulling the intake manifold and both valve covers, I'm not seeing any sign of a collapsed lifter. Now I am not quite sure how to proceed. I guess I'll put the intake manifold back on and fire it up with the valve covers off and try to feel for the culprit, and then take dial indicator measurements - my problem appears similar to what our host had in this video, but I'm not clear on what ended up being wrong with this engine: https://www.youtube.com/watch?v=0YPPsYbffAA
Attached are videos of my engine running before I opened it up, and the right bank cranking with a hand trigger attached to the starter relay slot (learned that trick from you CPR, thanks!). Although the sound does not come from the left bank (driver side), I opened up that side too and cranked it but didn't see any issues.
Looking for some expert opinions on how to proceed. I didn't catch his name, but Crazed Performance Repair is the best in the business for these issues and the only one I trust right now. What should I do?
Engine running:
Right bank cranking with starter:
Thanks,
Denny Smith
Denny's Repair Service
Elkhorn, NE
OK, I finally had time to dive into this repair. After discovering that I did not have a collapsed lifter after all, I ended up putting the intake manifold back on and starting the engine with the right side valve cover off (I learned that you can run the engine fine with the valve cover off for about a minute at idle before oil makes its way up to the rocker arms - if you need more time you can fashion a splash shield out of scrap sheet metal to block the oil from spilling out of the head; or you can just shut it down for several minutes and let the oil drain back down and start over).
With the engine running I could not tell by the naked eye that there was anything wrong with any of the 8 valves but I could clearly hear the tick. I used Mr. CPR's technique of feeling each rocker arm above the valve spring for smooth operation (my wife was in the driver seat in case I needed an emergency shutdown). After a thorough investigation I could feel the slightest clicking on the #4 cylinder intake valve where I had suspected my original collapsed lifter.
I removed the rocker arm from that position and discovered a bent pushrod. There were no misfires or any MIL illumination during these tests but I had previously cleared a P0300 and P0322 knock sensor code when I first learned of the ticking.
Here is what I found (#2 intake pushrod pictured left for comparison, #4 bent intake pushrod on the right):
These findings are exactly in line with what Mr. CPR posted in the YouTube video below and appear to be nothing more than a design flaw. I ordered a new pushrod from RockAuto for $3 and will install that for now. Mr. CPR mentioned in this video that he may be having a stronger set of aftermarket pushrods designed to fix this issue. Watch this for more info:
I will close this post by stating that during my original troubleshooting I discovered the oil overserviced by 2 quarts, so oil aeration may have been in play here, but I cannot see how this would cause a bent pushrod even if there was a mistime event for the AFM lifter. Maybe it's a coincidence, or maybe the oil aeration caused this, or maybe it's just a design flaw, I'm not sure.
For more information on how AFM lifters work, I found this video helpful:
Denny Smith
Denny's Repair Service
Elkhorn, NE