Tapping Noise On Rebuilt 6.5

[bertram31]

I recently purchased a 96' GMC 3500 Dually with rebuilt 1999 6.5 Truck runs very strong no issues except I started hearing a tapping sound at idle. The noise is pretty distinct. The motor has about 2000 miles on rebuild. Is this tapping noise something I should be concerned about. Appreciate your help. Tx. r/ Roland

[Robyn]

With the hood open and the little tapping noise just doing its thing, put a gloved hand on the back of the metal shield that covers the turbo charger. There is a nice slightly sloped spot on the shield.
If my guess is right you have the normal tic that these engine have at times. A rebuilt that has had new injectors and such put in will many times do this.
By placing your hand on the shield, if this is it it will drastically change the noise.

If this happens dont worry about it.
The injectors make a fair amount of noise when the close and this metalic noise can transmit up through the manifold and the turbo and the liitle tin can will make it sound nasty.
let us know.

My 94 Burb was quiet until I rebuilt the little beast and now it makes the tic but a hand on the shield will stop it.

I had a 93 GMC that did it from the git go. Took me a month to figure out what it was.

If this is it you can bolt a piece of lead sheet thats 1/4 inch thick over the back side of that shield and it will damp the noise out.
Robyn

[More Power]

Don't assume the tapping is the beginning of a mechanical problem till you've eliminated the injectors as a possible cause. Loosen one injector fuel line after another - looking for a change in the tapping. Loosening a fuel injector line will cause that cylinder to not fire (and the injector won't inject). This is like pulling spark plug wires to find a bad spark plug on a gas engine.

If you discover one cylinder that loses the tapping when the injector fuel line is loosened, try swapping that injector for another to see if the sound migrates with the injector. If it does, you've found a bad injector. If the sound remains with the original cylinder, it could be due to a mechanical problem with that cylinder. If the problem is mechanical, first pull the valve cover to see whether the valve train is doing all it needs to do, or if there's a lifter, pushrod or rocker problem.

Jim

[bertram31]

Thanx Robyn and More Power, will do the recommended checks you have recommended and get back with you on my results. r/ Roland

[hamold1]

I had a tapping noise which sounded internal...could hear more on rt side rear only from inside the truck. It started after I had the injector pump replaced, the mechanic reved the engine so high a couple of times to show me it ran fine, I thought he did some major damage with the high revs. Drove it 2 months like this....We pulled the intake so we could loosen the injector lines 1 by 1 , but after the intake was off I started the engine and the noise was gone. ?????????????? reinstalled intake with new gaskets and followed torque specs and sequence. No noise what ever it was was self inflicted when the injection pump was replaced.
Chris
2 1993 GMC 6.5td 4l80e no mods yet just getting started