Thread: loud tapping noise

My engine's making a loud tapping noise that I can't figure out. I was out on the highway doing a couple high speed blasts. On the way back home, I noticed the noise, which changes according to engine speed. It seems to be coming from the passenger front of the engine. I've taken both valve covers off and checked the rockers, springs, and pushrods. Looked good. Took the front cover off, chain, dampner, and gears looked good. Did a cylinder leadown test and all cylinders tested good. Oil pressure never dropped. No codes. The harmonic balancer is not cracked. I took the inspection cover off and checked out the flexplate while turning the engine by hand, saw no cracks. Drained the oil, no metal. Removed both belts and the noise is still there. I'm stumped. I thought if it was a lifter there would be a loose rocker arm/pushrod. I thought if it was a rod bearing oil pressure would drop. I took a video with my phone, but I'm having problems posting it. Thanks for any help/advice.

decided I would take the intake off and check the lifters. When I pulled the fuel rail off on the #1 injector I found a piece of plastic that had broken off from a electrical connector(the tab) wedged in between the injector and the head, blocking the injector. So that cylinder was obviously running way lean. What could have happened that could make the motor make this noise? Obviously if the cylinder was lean it could overheat ruining a piston, but wouldn't that have showed up on my cylinder leakdown test? I think I'll put the fuel rail back on and fire it back up to see if the noise is still there. If it is, I'm thinking engine teardown time.

How did it get in between the injector and the head? I would've figured you would've had a vacuum leak from that.

Earlier in the day, I had pulled the fuel rail off, the piece of plastic had broken off of the connector and fell down into the injector boss. I did not see it when I put the fuel rail back on, and when I pushed the injectors into place it just wedged itself in between the injector and the head. When I took the fuel rail off, the o-ring was tore, so I don't know how it wasn't spraying fuel all over. By the way, I put the fuel rail back on and the noise is still there.

I hope it's just a lifter, but this is a loud tapping noise. Lifters that I've heard before are more of a ticking noise. Bearings are more of a knock.

see if you can get that sound bite up!

here's the clip:


030109_142800.flv video by blown98gtp - Photobucket

could also be a cracked/worn exhaust manifold gasket.

pulled the motor today. found this upon inspection. #1 rod bearings are wiped. However, they rod journals and crank surface don't look bad. I'll measure with micrometer, but I'm thinking I could get away with new bearings and recondition the rods. On the other hand, I was thinking of finding a L36 to swap out the bottom end for higher compression. What do you guys think?

http://i285.photobucket.com/albums/l...gtp/rod007.jpg

http://i285.photobucket.com/albums/l...gtp/rod008.jpg

http://i285.photobucket.com/albums/l...gtp/rod009.jpg

http://i285.photobucket.com/albums/l...gtp/rod005.jpg

http://i285.photobucket.com/albums/l...gtp/rod003.jpg