Knocking Sound at Idle
 

For the last year I have been hearing an odd knocking sound at idle. No driveability issues, and while cruising is doesn't make this sound. However, when idling it makes a racket like the thing is going to throw a rod.

When I rev the engine it goes away, so it makes me think it isn't a connecting rod or bearing. Also, when the A/C unit comes on the rattle becomes consistent and less obtrusive, which made me think it had something to do with the compressor. The sound is so loud, and well the 6.5 in general, that it is tough to get an approximate location for the sound.

I checked all over for something loose to no avail.

Here are the sound clips, maybe someone has heard this and knows what is going on.

I couldn't download the sound files because of safari but a sticking injector will should like a rod knock how old are the injectors in your truck and do you run sea foam through it occasionally? Also I used 2 stroke oil in my fuel 1/2-1 oz per gallon of fuel this also aids injector pump longevity. Hope this help Mayhem.

I don't think they have ever been changed. I have never run Sea-Foam through it, but I have used several slickdiesel jugs with full tanks.

Sea Foam works wonders my injectors are maybe 4 years old and from time to time one will stick first time I heard that noise I was holy(edited) a long time diesel mechanic I know recommend the Sea Foam a while back and it's the only cleaner I ever use.

One more question Mayhem:

If an injector is sticking that will not cause the engine to run rough?

Sometimes it will like a loping action next time it does it look for white smoke this is unburnt fuel do you have a lot of white smoke upon start up?

Occasionally there is a puff of smoke.

That sounds like what we just went through and we had to replace the harmonic balancer. Listen to it carefully and if it is by the front of the engine than that could be the culprit. We got lucky and drove ours that way for a year until the pulley came off and got wrapped up in the fan. Tried to replace the belt and it kept coming off. Looked closely again and sure enough it was the harmonic balancer.
Also, I think it is this because we had the same thing where the noise got better with the A/C being on. It works like a counter balance and brings the motor back into balance. Good Luck.:jump:

That sounds like the problem. If it was a stuck injector I would see performance issues and white smoke, which I do not see.

Thank you very much. Will change it to see if that is the problem.

its been a few. how is the noise hunt going?