Hey all. I don't have a ton of knowledge about engines but enough to get em running. So here's the problem. For a while I've noticed a tapping or knocking sound. Like rod knock. I only hear it when I rev it up and after I let off I hear a tap tap tap for a few seconds and it fades out. Then I rev it again and same thing. I don't hear it when the engine is hot. I've pulled the belt off and same deal. So its not the alt. Or power steering pump or anything. I've got good oil pressure. Cold start runs about almost 70 psi if I recall right. Hot idle is about 30 and hot reved up is about 50 or 60. I've put in a new aftermarket plenum and gasket. New intake gaskets and throttle body gasket. New valve stem seals and valve cover gaskets. Replaced a stuck egr at the same time.I'm using Mobil 1 high mileage 10-30. Also added about half a bottle of Lucas synthetic oil additive. It did help a bit. She's a 94 and has 210k on her and a tranny rebuilt 4k ago. And the frame and body are still really good. So I'd really like to keep it for a while. Kinda hoping to make it to 300k. So I've been wondering. Wouldnt a rod be audible all the time/ could it just be a wrist pin? Or flex plate? It is audible from front or either side just the same doesnt seem as loud underneath but its hard to tell. Any help is greatly appreciated.

 

Did you listen close to each valve cover? Could be a lifter tapping.........

 

Your description sounds a lot like lifter tick.

 

use a piece of pipe about 2-3 feet long as a stethoscope and listen at every part of the engine for where its loudest.

be very careful of moving parts, battery cables, starter cable !!!!!!!

 

ive tried to listen to the lifters before but ill try using a piece of hose and see if i can hear anything.

 

Does the knock/tick go away when the engine is revved? If so, I agree that it's most likely a lifter. I had a lifter do that after I rebuilt the engine in my 5.2L.

 

yes it does. and i only hear it for a few seconds after the engine returns to idle. then it fades out. sometime ive noticed after about a minute when i start it cold i hear it for a minute then it fades. but i rev it and its gone. id be happy if that's all it is. also when i replaced the valve stem seals i did check all the push rods and all looked ok. the had some wear on the ends but nothing i wouldn't expect with 205k at the time. also checked to make sure they weren't plugged inside and they looked good. none looked bent if i put em on a flat surface. then i put it all back together and torqued everything back down to spec. i had replaced the seals and plenum cause i had been burning a qt of oil every 1k miles or so. now i haven't used a drop of oil and no more smoke from the exhaust. the plenum plate was warped and caused the gasket to blow. i bought the aftermarket 1/4" aluminum plenum plate so hopefully it will last.

 

Yep, just a lifter losing pressure. You'll be fine.