I ran my 93 a little hot, 220 degrees, it never overheated as we know it. pulled over, sounded and ran fine, went home and got out to open the gate and heard a fairly loud ticking.
Still have good oil pressure, runs the same, same egts. have put 150 miles on it since and no change. adjusted valves again, all ok still. Took it to reputable diesel shop and couldent figure it out for sure. I cracked #5 injector open and the noise goes away.
So, now where do I go. If it was an injector stuck shut it would miss, If it was stuck open it would over fuel #5 and heat up quicker from cold start. checked all 6 with infared thermo and all the same from cold start to 100 degrees. Rod knock would cause low oil and loud from below and probably smoked it by now, its on top it sounds like. Wrist pin gone bad?? But wouldent it knock all the time also even with no fuel? Im stumped on this one. take a guess, im outta ideas and dont have time to tear the engine down just to guess at it. .

 

You can have one injector that is sticking and still have a decent running engine when you're "at RPM".
The pump overcomes the sticky nozzle. At idle the pump output pressure is less and so the injector sticks.
Unless you plan on putting some upgrade injectors in the truck (better than my next suggestion) you can have your old one's pulled out, pop tested, check for spary pattern and matched, then reinstalled. .... You're good to go.

pb...

 

Burned injector . . . bad spray pattern, causes mild fuel knock. If you have a good relationship with a cummins or injection shop, I would buy a set of re-manned injectors, replace #5, and see how the engine sounds. If it still isn't even, swap through the other re-mans in the set to find one that sounds good. When you find one that sounds good, return the other five, and you're all set to go. We used to match our re-manned injectors by ear all the time .

If you can hear the problem, you need to fix it -- it'll burn your piston eventually.