2nd Gen 5.9L Cummins Knock at Idle
 

One of our rigs was run low on oil. It never lost oil pressure but the turbo was starved for oil and failed. Now the turbo has been replaced started it up it white smoked for a while and soon cleared. Took it for an immediate oil change. It runs fine, smooth the knock is at idle and goes away when reved. The knock is also not as loud when fully warmed up. The truck doesn't miss the power seems the same smooth running just knocking at idle. The sound seems to be coming from the top end. I suspect an injector or injectors. The oil level is fine and doesn't smell like diesel. Is there another way to check for diesel in the oil? I called the original owner he's said the injectors are original the truck has just turned 250k miles and I had the Valves adjusted at 250k miles. Like I said the rig never lost oil pressure and was topped off as soon as it was noticed. I have both read and been told that it could be a ruined cylinder or hole in a piston worse case. Bent pushrod or loose valves. Or Injector/Injectors. The turbo was definitely ruined bearings failed to the point that the turbine was scored the housing both sides and lots of oil dumped both intake and exhaust. When the turbo was replaced there was no noticeable debris in the tube between the turbo and intercooler other than oil. The fact that it never lost oil pressure and runs smooth no miss no loss of power leads me to believe that the motor is not hurt. I ordered 6 injectors and will replace them as soon as they arrive. 250k on original injectors, to me it just makes sense replace them all, it's more than time!

Thoughts opinions suggestions am I heading in the right direction? :humm:
Thanx
Randy

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More info on the rig
99 dodge ram 3500 dually 5spd
2nd gen 24valve 5.9L cummins
HX40 Turbo t4 flange with adapter
4" straight exhaust to axle with turndown
other than that stock
a lil more than 250k miles runs smooth no miss lots of power
oil leaks

Sorry to hear about your misfortune. At first I was thinking a possible piston wrist pin issue, but you indicated the knock subsides when warm. I would say you may have a bad injector(s). You may have to wait and see what happens when you replace your injectors. Just how low was the oil level when the turbo failed?
Some time ago I had an injector go bad on me, and it made a loud knocking sound. Thought I spun a rod bearing. Engine ran smooth with no miss. Turned out to be a bad #1 injector. Went ahead and replaced them all. Hope your fix is as simple as a bad injector. Sorry Im not much help, but I think your headed inthe right direction. Good luck with your fix.

almost 2 gal of oil! The only saving grace was aways had oil pressure! :argh:

I have heard of another method of checking for diesel in the engine oil but I can't remember the particulars. something about blotting a paper towel and a bullseye but again I'm not sure. :argh:

Two Gallons! YEEEOUCH, thats quite substantial. Theres a good chance there may have been oil aeration, causing oil pressure fluctuations faster than could be registered on your oil pressure gauge, but still showing pressure. I can certainly see why the turbo went south.
Im not sure about the other method of checking for diesel in the oil. You indicate that the knocking sound is coming from the top end of the engine. That, to me, sounds like an injector issue. I hope thats all it is and nothing worse. Maybe a diesel tech can chime in and pour better light on the subject. keep us posted if you can. Be interesting to find out what the true culprit(s) is. Good luck!

After getting her back to the shop that day and evaluating what had happened, the way she sounded and the smoke bellowing out the pipe, I really considered her damaged beyond repair. The damage to the turbo was obvious and we knew a replacement hx40 would be in order even if we need a new motor so I ordered one. I am just amazed after swapping the turbo, changing the oil and running it for awhile how well it's running smooth as ever power is still there and no miss, just that knock at idle. :humm: The injector swap will tell all and we will post!!!! :dang:

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Either way this goes the parts that I'm swapping can easily saved for a replacement motor if it truly comes down to that! I am just amazed at the way this girl is running! :humm:

Damn diesels can be a real PITA to diagnose, expensive to repair and maintain, expensive to modify...............ah but I wouldnt have it any other way!!! :c:

I am not sure about the 5.9 but the big cummins in our straight truck had a bad piston that had a collapsed skirt. It ran fine but had a knock that sounded like the top end or bad injector. A piston slap sounds like you are describing sometimes. I pulled the head and pan, honed the cylinder and replaced the piston and all was well. On the big ones it is usually the #6 that has the problem.

Gradyc your tale does not inspire confidence!!! However it could very well be the problem I don't believe I have room to drop the pan in the truck! The new injectors are on their way! I went ahead and asked for a new set of O-ring for the fuel tubes and feeling optimistic that the injectors are the culprit, I asked for a set of rv275 injectors with aftermarket bodies for 1998-2002 and a Bigline kit 24v as well. If the injectors aren't the problem and the valve train shows no signs of distress the head comes off and we will see what we see! :scare2:

Bein it goes away with warmth I would be pretty suspicious of an injector just once it warms up it clears completly or still there?

I haven't run it much more than that one day once we put the turbo on changed the oil left it idling for a good while that's when I noticed the knock or tap was barely noticeable but the drive back to the shop every time I came to a stop the noise was there. Waiting for the new injectors is like watching a pot boil!!! :argh: