JG2001

Hi all,

New to the forum and was hoping you could help me diagnose a "rod knock" on a 5.3L LM7. Sits in a 2001 Tahoe. I am a bit new to all of this, so I appreciate the help in advance. See video below.

Engine: 2001 5.3L, 174k miles. 40 lbs of pressure at idle.

Issue: The engine just started making a loud knock on start (louder than the infamous GM "piston slap" that goes away after warm up. Louder than a lifter tick for sure). Started overnight - prior to that, nothing. Here's the interesting part - the knock goes away under load. After a few revs of the engine, it completely goes away (~20 sec. mark in video). My guess is that oil is not getting to somewhere in the engine under idle, but under load, there's enough pressure etc. to circulate oil to that spot.

See video below. Any idea of what this could be? Collapsed lifter that pumps up under load? Blocked oil pickup O-ring? Failing Oil Pump?

Thanks for the help from a newbie. Excited to learn from you guys.


Jack

Also, one last thing -- How bad is it to run the engine like this? Obviously its a bad knock, but will a few test runs to diagnose significantly damage it? Thanks for bearing with me. Appreciate the help.

LS1Formulation

iTrader: (13)

Well, it's not a rod knock. It probably IS a collapsed lifter, actually. With all that clearance in the system, it's going to get loud. Running it to diagnose it won't likely do damage, but it's going to hurt something if you keep driving it. Looks like you're going to have to pull the heads and swap lifters.

G Atsma

Like LS1Formulation said- That isn't even close to a KNOCKING sound. Valvetrain clatter.
I too suspect bad lifter(s).

Full Power

LM7 Love you LONG time.
It'll do that for another 100,000 miles, probably outlast the transmission behind it, twice.
IF you " get tired" of listening to it, you'll have to pull the heads, great time to push in a nice torque cam, lifters, and new valve springs.

strutaeng

My 06 Suburban LQ4 has an intermittent lifter tick. It will usually do it when I jump on the highway, then by the time I get home in another 8 miles it's gone. My engine is at like 262k.

The sound is top of the engine like yours, but mine seems "slower", like half the rpm of the engine. Yours sounds the same as the RPM.

On the rare case it's still doing it when I get home on mine, I've listened to it with a stethoscope, and I can definitely hear it near the top. My plan is to replace lifters, very mild cam (Summit, I can't remember the number), refreshed heads I already got, basically a top end refresh.

Maybe you should pull the valve cover to see if you see anything in there.

Also, the twitching oil pressure gauge is concerning...

Full Power

Another thing to check is the number of REMAINING exhaust manifold bolts on either side of the engine.
Fewer than six bolts per side will sometimes leave a ticking sound that CAN be louder when cold.

dawgs74

Cracked flexplate??