Knocking and Vibrating 2005 W900 Cummins 400hp ISX

BigPerm · Dec 19, 2012

Hate to say this..but the 2007 Pete ISX-500 I was driving had the same problem. Loose nut on trans output shaft.

Jerzy · Feb 24, 2013

Front balancer on engine?

Lynzee · Aug 8, 2015

shcbbe said: ↑

I have a 2005 w900 with the Cummins 400hp ISX motor. I have had a situation with this truck vibrating at a stand still or parked just idling, it will also knock or vibrate against the floor board when under a load or pulling a hill. I was wanting some ideas on what may cause this. I have had the U joints checked and they were okay. I am thinking that maybe the dampener is worn or the clutch springs are broke. Am I off base with my analysis? Note it has been on going for about 2 years and it seems that the problem is about the same.
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That's just a Cummins for ya lol that's just the sounds they make. U should hear an N14 plus Cummins its sounds like the pistons r gonna come flying out but it just has a lot of smack to it at an idle

CornbreadT680 · May 2, 2016

2015 T680 ISX1 , everytime I let up on the accelerator or let off to downshift. Sounds like something is loose and vibration bad. It's got 261k. Think it's the clutch needs adjusting?

BigPerm · May 2, 2016

CornbreadT680 said: ↑

2015 T680 ISX1 , everytime I let up on the accelerator or let off to downshift. Sounds like something is loose and vibration bad. It's got 261k. Think it's the clutch needs adjusting?
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I'd look at a broken/loose motor/trans mount or loose output yoke to start with.

aw12345 · Aug 14, 2016

Just maybe one or more dogs of the intermediate clutch plate broken off? Will make it shake and vibrate bad

Petegraintrain · Mar 7, 2023

VisionLogistics said: ↑

I'm getting the same symptoms. Unstable Engine Speed, engine knock (internal) when pulling hills in the powerband. You can hear a rumble in the exhaust at idle (aside from the normal clean, smooth exhaust note) and see the tach surging 100 rpm.

Things we've tried:

1. Rebuilt the engine 7k miles ago
2. New cam, and 1 new rocker
3. New timing actuator
4. New exhaust gas pressure sensor
5. New turbo and turbo actuator
6. 2 gallons of lucas
7. New CAC
8. New Radiator

It's a CM870 (ISX 475 EGR).

With what sounds to be a fuel knock, and the unstable engine speed, I am leaning toward it being in the fuel system. Maybe sucking air, or an injector going bad. Poor power, and fuel economy really suffering. It also occasionally throws a code for "Power imbalance detected between cylinders". So I am going back to cummins tomorrow and hope they can fix it. I'll have them run a power balance test to see if any injectors are putting out more than 100% suggesting a leaking injector neighbor.

Any other ideas on what to have them check? Fuel pressure, and presence of air bubbles probably, eh?
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Gonna bump a REALLY old thread here. Did you ever find this issue? I have the same exact thing

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