hey all,
i have a noise coming apparently from the driver's side of my engine that i haven't heard before. it's kind of a high speed tapping or chirp. if i hadn't just replaced it, i'd suspect my lift pump. it only seems to happen at higher revs (around 2k) but is very inconsistent. doesn't happen when i rev it from under the hood. infidel suggested replacing the overflow valve, which i intend on doing, but was wondering if anyone has any idea what this sound might be and if it is safe to drive or if i might damage my injection pump or anything? (there are no other symptoms that i know of other than the sound, although i am seeing more dark smoke than i am used to, but that started long b4 the tapping)
thanks

 

turn engine off and start pumping the lift pump you should hear a sqeak coming from the overflow valve and see if it sounds like your squeak your hearing. If it has never been replaced you should go ahead and replace it.

 

yes, i can hear the overflow valve when i pump the lp while engine is off, but that is not the noise i'm hearing while it's running. i can't imagine what else it would be other than my lp unless it was the inj pump, which is why i'm afraid to drive it

 

Its hard to believe its the IP, how about your belt? There is a gasket under the intake elbow check for air leakage thier, also check all other intercooler boots clamps for tightness (this could be why you have more smoke). Might also try a sthethescope or a piece of wood and go over the area good. Does it really sound like a chirp on that side?

 

yeah, it's like a high pitch, rapid, mechanical tapping, which is why i think it would be the lp, but don't know for sure.

 

Based on what you have eliminated, I would suspect the transfer pump is the source of the noise. What happens is the internal piston on that pump becomes worn and will slightly hang in the pump bore and create excessive clearance to the pushrod from the camshaft. A change in the temperature of the engine should cause the noise to change or go away, if that is the case. Very short term it is not critical, but it can be hard on the fuel pump cam lobe, or the internal seal on the pump piston can fail and force diesel into the crankcase.