My truck (the '01 6-speed) has had a light 'knock' for about 3 years. I have never been able to find where it's coming from. Now, it seems to have gotten a bit worse. Now, over those 3 years I've put 55,000 miles on it.
About the knock:

I can't hear it at idle - sounds like any other 24 valve engine. When I bring the RPMs up it rears it's ugly head around 1700 RPM. You can 'feel' it in the accelerator pedal and in the floor, too. And, the exhaust sound has an 'irregularity' to it that goes along with the knock. When driving, you can hear it under light to moderate throttle (the stacks drown it out when you really get on it, though).

Because of the exhaust sound irregularity, and the fact that it's been doing it for so long without self-destructing, I thought it might be a fuel problem. This week, I put a brand new set of injectors in. No change. Then I 'borrowed' the vp44 from my other truck. No change. Went and put compressed air in each cylinder through the injector hole - no leaks out any intake or exhaust valves, and no cylinders are leaking pressure abnormally into the crankcase past the rings.

Perhaps I'm going nuts, and it's just a 'normal' noise in the exhaust, and the stacks are just 'transmitting' it into the body of the truck and that's why I feel it in the pedal/floor.

I'm going to send an oil sample to Blackstone next week, I'll post the results here. Until then, does anyone have any idea what this noise might be?

 

maybe you've got a pitted bearing. Thats just now starting to wear more? its possible, maybe worn pistion pin? you try a stethascope? they can help locate the area of the engine thats making the noise, tell its its bottom end or not. bottom ends not too bad you can always roll in some new bearings. But Your sample should peg it. I'd be interested in the results.

 

you could possibly have a deformed crown on one piston so the compression and burning pattern of the diesel is different than the others. Bad thing about it is that you won't be able to find it unless you pull the head off. How did the injector tips look. Any of the holes pluged or any mynute deformity in the nozzel? I wouldn't be inclined to inspect a bearing. If it was scoring you would be hard pressed to not spin one in 55,000 miles. But worth a try to look. But to actually find it your looking at an inframe basically.

 

When I pulled the injectors, #1 and #2 had a bit more carbon on the end of them. However, I saw the same thing when I changed injectors on my other truck, so I didn't think anything of it. Once I cleaned the nozzles off, they looked good and didn't have any plugged holes.

 

Diesels have wierd "engine bending" noises. With over 55,000 and still running, it ain't gonna quit soon without some more warning. Since the injectors didn't change at all, you have normal cyl leakage, another pump. You have went the gaumet. We tend to get paranoid and drill in on a sound. Naturally it gets louder the more you get tuned to sound. Buddies generally don't help, cause it's """way worse then mine""". JMHO

 

perhaps a weak or cracked valve spring, or maybe a cam lobe not quite to spec. just a thought.

 

Interesting, I hadn't thought of those. I'll have to check them the next time I've got a weekend free.