Hey so I just put a 97 6.5 into my 95. It didn't knock before I put it in but it didn't idle as low as the it is now that's it in my truck anyways, what I ve done Is, 8 new Bosch injectors (made it a little quieter) vacuum pump w/ new pulley, new serpentine belt, fresh oil and coolant, newer harmonic balancer. The knock only is heard at 600 rpms. At first I thought it was oil psi related but after warming the truck up keeping the idle at 900-1000 the oil psi dropped to almost 40 and there was no knock. Im unsrue what it could be now and im really hoping its not a big fix because I have been working o nthis thing for over a year without driving it and im sick of it sitting. thanks for any input

 

Hey, injectors can sometimes cause this knocking. You said they were new, but they could have gotten a little spec of dirt in them during installation. I replaced mine, one knocked a little but then it went away.

 

FWIW. Some new injectors may knock for a bit.
Air in the system can cause injectors to knock loudly too.