5.3 Intermittent Knock

[robertsjm711]

All,

I have a 2002 5.3 with an intermittent knock. I bought it last summer on Craigslist and have ran it for the past month or two with only two times with the knock. With the exception of these two instances, I drive it hard and easy, highway and in town. It seems to do great in town, but when I get on the highway and have constant RPMs it knocks, but not every highway drive. But the kicker is, before I get home it goes away, usually 10-15 minutes. When it does knock it is a constant volume and type, except speed with RPM and I can't get it to return.

Before I installed it I removed the pan to give it a once over and there was no sludge. It still had the oil in it, it was used and looked really good. Visually checked the pistons through the plug holes and they didn't look super carbon covered. I checked to oil pressure at that time and it was within GM spec.

It is mated to a Muncie 4 speed, and it is present moving or not and increases with RPM.

This is not a lifter tick, but a concerning knock.

Thoughts? Experiences?