7.3 knock

[vanillavanwinkle]

Hey everyone, after reading through the seemingly thousands of threads about knocks, I can't figure mine out. I have a 1990 7.3 idi with a turbo off of a 94, only running about 5lbs of boost. Engine started knocking suddenly while cruising on the highway, I've put about 10,000-20,000km on it since then, and the noise has never gotten worse. It starts the second you fire it up, doesn't seem to change with temperature. I've replaced all the injectors myself and had the crankcase pressure and cylinder compression tested by a local diesel shop. Everything came back good, save for some "very fine specks" in the oil filter. There's a puff of smoke out of the exhaust in time with the knock, and the knock seems to stop when I unplug any injector. Engine also has fresh piston rings and crank bearings. The shop suggested possibly a wrist pin in cylinder #8, but I don't think unplugging any injector would stop it. Any ideas? Thanks

 

[KansasIDI]

What color is the smoke?

 

[vanillavanwinkle]

Smoke is just white/gray, doesn't seem to be coolant from what i can tell. The truck also has the reburn thing deleted, can't remember the name of it. But it's just got a road draft tube that the previous owner routed into the exhaust

 

[KansasIDI]

Smoke is just white/gray, doesn't seem to be coolant from what i can tell. The truck also has the reburn thing deleted, can't remember the name of it. But it's just got a road draft tube that the previous owner routed into the exhaust

CDR valve. I would recommend either disconnecting your road draft tube from the exhaust or putting a CDR back on. It’s a crankcase vent. I would actually recommend to just start there, then see how it behaves and begin further diagnosis

 

[vanillavanwinkle]

Id love to cause I hate the smoke this thing pumps out, but can't find one locally. I have tried disconnecting the RDT and rerouting it and all that, doesn't seem to make any difference in terms of the knocking

 

[KansasIDI]

Id love to cause I hate the smoke this thing pumps out, but can't find one locally. I have tried disconnecting the RDT and rerouting it and all that, doesn't seem to make any difference in terms of the knocking

What does the knock sound like? Raspy, clicky, thud, thunk?

 

[vanillavanwinkle]

Kind of a metallic thunk, like someone's smacking the engine with a hammer. I'll try to get a video of it in a little bit

 

[Kdo58]

I would pull the valve covers off and see if anything is loose.

 

[The_Josh_Bear]

Boy that's a head scratcher for sure.

How do you unplug an injector on an IDI?

I found that my inspection plate on my ZF-5 was bent just right so that a part of the LuK flywheel would hit it while running. Dropping the plate immediately identified that issue, I bent it back a little and now it's fine.
But of course that sound won't go away by loosening an injector line...

 

[vanillavanwinkle]

Sorry, meant loosen not unplug the injectors haha. Yeah I'm not sure, I thought maybe it was the dual mass flywheel, so I took the inspection cover off and it looks fine, doesn't change with clutch in/out or anything like that either. And yeah pulling valve covers and checking valve train is next on my list, wondering if it didn't bend a pushrod or something like that and with the drop in RPM when an injector line is loosened off, it just quiets it down

 

[IDIBRONCO]

I thought maybe it was the dual mass flywheel, so I took the inspection cover off and it looks fine, doesn't change with clutch in/out or anything like that either.

That's usually not a constant knock. It usually happens at engine start up and goes away when you rev the engine a little bit.

 

[vanillavanwinkle]

That's usually not a constant knock. It usually happens at engine start up and goes away when you rev the engine a little bit.

Ahh okay, yeah no this never stops or changes volume or anything, truck runs perfectly fine though

 

[vanillavanwinkle]

Here's a video, pay no mind to the random wires and the beautiful fill cap, previous owner crap I'm slowly undoing lol

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[904STA]

Curious what the fix is. My truck has the same issue to a T. No difference when cracking injectors besides smoke going away.

 

[IDIBRONCO]

Curious what the fix is.

Me too. This one has me stumped.