Hey guys was headed to school in the truck yesterday. Has 140,000 miles on it. Its a 2003 5.3 with 243 heads milled .030 for compression LS7 lifters set to .075 preload. Pushrods are 7.325 length and springs are comp .650 lift springs. Cam is comp 216/220 .525 .532 lift. Passed a person and hit 85 mph in the process, which is not unusual. About two miles down the road I look down and my oil pressure is at 15 psi @ 2000 rpms. Normally I run at about 50-60 psi at 2000rpms. Not two minutes later I hear what sounds to be all the lifters chattering. Sounded like a bear trying to get out of the motor. Had to drive it the last two miles to class for a test I couldn't miss. Checked the oil after and it was fine. Decided to go tow it home with my father in laws help. Started it to load it up on the trailer and the oil pressure was back up to 35psi and engine was pretty quiet. Started it again when we got it back home and the same thing. Wondering if any of you have had this happen. I am planning on playing it safe and not driving it in the case that I ruin my block. The oil pressure drop is very concerning and the noise proves a problem. Afraid if I let it get warm it will do it again. Any thoughts? Cam is not that big and I have made sure to set the valvtrain up correctly or so I thought. Who knows it might have been something else in the motor making all the racket.

 

The relief valve in the oil pump could be going bad, it's where I'd be looking first anyway.

 

Sounds like a pump, actually sounds like how i killed the 5.3 in my 99 but was hours in either direction from either home or my moms, with all of my kids in the truck. And already had the 6.0 on the stand waiting.... took out 2 rod bearings and eventually the rods, along with eating the cam, all from a bad oil pump!