Faint knocking under light throttle

[snakeye]

I'm hearing a very faint knocking while cruising whenever I give light throttle at low-ish rpm. Sounds kind of like a woodpecker, but it's very faint, barely noticeable, so much so that I think it maaaay be normal? Not sure... It's very responsive to the throttle, like instant noise as soon as I press it. Does this sound like the injectors? I'm considering upgrading the nozzles, but I'm wondering if I should maybe try some kind of injector cleaning additive first, see if it does anything. Anyone has any success with any of those?

 

[csstevej]

You can do the diesel purge straight from the can and see if that helps .
Run a line from the can to the intake of the pump via a small lawn mower inline gas filter and have the return line from IP go back into the can .
Run the engine at idle till most of can is gone.
Reattach everything that was disconnected, pour any remaining diesel purge into fuel tank and go for a spin and see if it makes a difference.

 

[Smokin' Dually]

How many miles are on it? I heard a slight knock after a 30 minute drive on the highway. I kept the driving time to a minimum until I replaced the injectors a couple of weeks later. That fixed the knock. According to Drive By Wire, the original tips are only good for 150k miles due to the virtual elimination of phosphorus from diesel fuel in '06 for the '07 diesel EPA tier.

 

[454k30]

This was how i described my engine's noise after a lifter had failed and just before it collapsed completely, taking the corresponding cam lobe with it. I would suggest pulling the valve cover and having a close look at the lifters and cam. I wish I had done this.

 

[snakeye]

Sorry forgot to mention, car has 224k milles on it now. Honestly I'm leaning more towards the injectors, especially at that low-ish mileage. If it were a lifter, given that that's a mechanical problem, wouldn't the sound be present under all conditions, even without fueling? I think I'll give diesel purge a shot, and then if that doesn't work, then it's onto countless hours of reading trying to resolve my indecisiveness about what nozzles I should be getting.

 

[csstevej]

Pop the valve cover and look at the lifters, see if any compress slightly when pushed down with a non marring tool. Any any compression movement…. Well then there’s your culprit.
Won’t cost you anything but some time.

 

[Nevada_TDI]

Sorry forgot to mention, car has 224k milles on it now. Honestly I'm leaning more towards the injectors, especially at that low-ish mileage. If it were a lifter, given that that's a mechanical problem, wouldn't the sound be present under all conditions, even without fueling? I think I'll give diesel purge a shot, and then if that doesn't work, then it's onto countless hours of reading trying to resolve my indecisiveness about what nozzles I should be getting
At 224k some may say your nozzles should have been replaced 74k miles ago
/QUOTE]

With the right tuner, nozzle size can be adjusted for proper fueling. If you think sometime in the future you may want a bigger turbo, the .216's would be a good place to start. If you do not plan on a bigger turbo, then .205's and a 18PSI tune will make a ton of power and great FE too.

 

[Windex]

You say above that it's responding to throttle, but does it "track" with throttle/engine speed? IE does the noise rise and fall in frequency related to engine rpm? Reason why I ask is the N75 valve can sound very much like a woodpecker, but the noise frequency is fixed. It will respond to throttle, but not correlate to engine RPM

 

[snakeye]

I'm really not sure if it matches the rpm. Possibly? It's very fast and faint. I did some listening/experimenting today and noticed that I could hear it while idling, or at lowish RPMs while stationary, and that pressing the clutch in quiets the sound. Tested it while cruising as well, pressed the clutch in while maintaining the same RPM, and the sound goes away.

Kinda stumped now. It's nothing like the can being tossed around sound of a failing DMF, but could it still be transmission related, and if so, what?

Just to make sure, I think I'm going to pull the serpentine belt when I get a chance, just to rule out any pulley, as I've had a similar ticking noise (albeit much louder) coming from a failing compressor pulley once, and a failing alt pulley can show weird symptoms.

 

[snakeye]

Pop the valve cover and look at the lifters, see if any compress slightly when pushed down with a non marring tool. Any any compression movement…. Well then there’s your culprit.
Won’t cost you anything but some time.

So I did this, no movement in the lifters from what I can tell. I don't know how hard you need to press, but I did as hard as I could with the back end of a plastic spatula.

I also got lazy but eventually ended up pulling the serpentine belt... cause the tensioner snapped. Alt pulley was seized. Replaced pulley and tensioner, but the sound remains.

I just received some new nozzles, I guess I'll install those next, see if it'll solve the knocking.