knocking noise

[DaveS]

Does anybody have any idea what would cause such a knocking noise. It seems to be coming from around the air intake/turbo area. Its pretty loud, can hear really well at idle. Engine runs normal, nothing else out of the ordinary. I just put on a new air intake from SSDiesel but noise was there before I did that. Could bad injectors cause such a noise?

Anyway.....very annoying, just hope its nothing really bad is going on. Thanks in advance for any ideas.




1995 3/4 ton chevy, 6.5 - 90,000 on second engine

[sixnickel]

Knocking or popping?? Take a piece of heater hose about 3' long put one end to your ear and probe around looking for the noise. If it is in the intake it could be a problem with a intake valve or a exhaust valve not opening all tye way. Let us know where the noise is coming from and we will go from there.

[DaveS]

Wow, drove it today, and on the way home the noise got so loud I thought it
was coming through the hood. I lifte the hood and I think the noise is definitely coming out of the air intake. Engine did not act any differently though.

Where should I start, to diagnose?

[DaveS]

Hey Sixnickel,

forgot to

[DaveS]

Hey Sixnickel,

forgot to mention, the noise is kind of a popping noise, maybe exaust like?

[grancito]

blown manifold gasket on one cylinder will make racket. Mine is doing it and I found two loose manifold nuts. Tightened up the noise is not too bad and not increased.

[94sub]

double check your harmonic balancer and pulley. The rubber around the pulley is famous for hardening due to heat and cracking away in chunks. This will make it sound like the world is coming to an end up front.

[TedReminder]

If the engine is shaking and missing, I would look at intake valve springs. If an intake valve is hanging open it will make the noise you describe. Spring can be replaced pretty easy with head on engine. Been there - done that. To check, pull the upper intake plenum and listen in the intake runners with a hose to your ear with engine running.
Ted

[sixnickel]

I sounds like it could be a valve problem. If the engine still runs Ok but pops my guess it's a exhaust valve not opening all the way for some reason. Bent push rod, bad rocker. bad cam. When a exhaust valve doesn't open the cylinder can still fire but the exhaust can't get out. So when the intake valve opens the exhaust backs out through the intake valve and that is the popping you here. IF the engine runs rough and skips it could be a broken intake spring. If the intake valve is hanging open there is a good chance the pistion is hitting the valve at TDC because there is no room in there for the valve to be open with the pistion up. I would say it's time to pull the valve covers and see what's going on. Good luck!!

[grancito]

Perhaps I should look at that because there is a pulse coming back out the air intake.

[DaveS]

Allright, thanks for the ideas, I don't think its a loose exaust manifold, I've heard exaust leaks and its not that sound, I ordered a haynes diesel book and am going to look at the heads and see whats up. If you have any hints about this procedure...they would be appreciated.

[sixnickel]

One other thing I forgot is the rocker arm buttons. these are nylon things that hold the rockers in place side to side. check out SSDiesel Supply part#s ssd-209 and ssd-076. If these fail the rocker can slide the valve stem and mess things up.

[grancito]

I pulled the plenium off mine today and listened with a hose, and no unusual sounds from the intakes.The noise has decreased since putting a pint of ATF in 20 gals back 70 miles. When I turned the plenum over, it looked like a virgin, don't see how anything gets through there. I remember a post that described a modification, but didn't take much notice as mine is an "F" vin and thought it had the open type. ¿Anyone give me the search link? Thanks.