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?

Gonna get some SeaFoam and try it first.

Ordered a harmonic balancer today. If the Foam doesn't work then I will have the balancer on hand to swap it out if necessary.

If it's the harmonic balancer you will be able to move it back and forth by hand, the rubber deteriorates over time allowing the play it's more of a clanging noise than a knock.

It is more like an inconsistent rattle, like a loose bracket. It goes away with any sort of revs and smooths out when the A/C unit kicks in.

It's probably not the harmonic balancer the noise would speed up with engine rpm it may be the compressor???

That's was my first assumption. Maybe I can take the belt off and let it run for a short bit.

I know there's a few weeks on this post, but i just went through this - had a "rattle" in the front of the engine at idle and low speed, out of the blue. Started peeking around under the hood with the engine running and noticed the balancer had a wobble to it, so I replaced the balancer and the pulley in front of it. Truck was noticbly smoother running and quieter, but the noise was still there - it almost sounded like a heat shield rattling at lower RPM and nearly gone at the higher engine speeds. That turned out to be the vacuum pump starting to go. Still had vacuum, but was dying. Replaced it, and now all is good.
The bad part is that all these bits had sort of failed in unison. If the pump hadn't start to whine, I never would have noticed the balancer being out of true and that could have gotten pricey. I would slip the belt off the engine and run it to check and see if your noise goes away - you might be able to isolate what is is. Or, you might have fixed it and put 1,000 miles on it by now...

Nope. Just got two cans of SeaFoam through Amazon. Half price than OReillys.

Already got the balancer but haven't installed it. It is my work truck, so I have to schedule time for maintenance.

There is an annoying squeal coming from the vacuum pump area and I have suspected it needs replacement for some time now. However, I plan to get a programmed ECM and a mechanical wastegate do just do away with the vacuum pump, EGR, and the bank of crappy solenoids that control them.

Found the problem.

Saw fresh metal on the bolts of the balancer pulley. They were making contact with the "arms" connected to the outer ring of the balancer pulley. The composite had sheared from the inner ring completely.

This is why it went away with revs and why the rattle became steady when the A/C kicked on.

NAPA came through with the part within 24 hours. I removed the belt, shroud, and fan. It took an hour to remove and replace.

Now peace and quiet.