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Old 04-11-2018, 04:19 PM   #1
DDually
 
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04 Cummins problem, intermittent knock

I have a weird problem on a friend's 04 auto truck with 170k miles.

It has a noticeable knock when driving and rolling. It doesn't knock at all when it's sitting there idling in park, drive, reverse, or nuetral. It doesn't smoke at all, it has no notable blow by, and the oil pressure is good according to my mechanical gauge. I was thinking about pulling the valve train off to see if there is anything weird going on in there. Another thing to note is that it is matched with engine speed, not vehicle speed. It idles really smooth too, it doesn't feel like it's running on 5-1/2 cylinders or anything.

I was thinking maybe a cracked flex plate.

Is there anything else that would making a rod knock type sound?

Is it worth check compression if there isn't bad blow by?

Is it worth having the injectors sent off to be checked if it doesn't even haze at idle or cold start?

This is kind of a beat to crap ranch truck and it's been used and abused.

Short story: knocks when moving, no smoke, no blow by, doesn't knock when idling or sitting in drive.

Thanks,

Jared
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Old 04-11-2018, 04:23 PM   #2
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Converter or flexplate bolt backing out?
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Old 04-11-2018, 04:27 PM   #3
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I would check rail pressure and look for a spike when it starts the knocking. Could be a sticky FCA if thats the case.

May run a dose of Diesel Kleen through it as well, I have seen that fix similar problems.
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Last edited by SPEEDSHIFT; 04-11-2018 at 04:29 PM.
 
Old 04-11-2018, 04:37 PM   #4
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Quote:
Originally Posted by RacinDuallie View Post
Converter or flexplate bolt backing out?
I have had that happen, it was to the opposite effect of his though. Rattled terribly at idle and cleared up under a load.
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Old 04-11-2018, 04:42 PM   #5
DDually
 
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Quote:
Originally Posted by SPEEDSHIFT View Post
I would check rail pressure and look for a spike when it starts the knocking. Could be a sticky FCA if thats the case.

May run a dose of Diesel Kleen through it as well, I have seen that fix similar problems.
Will do. Ill try both.
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Old 04-11-2018, 04:43 PM   #6
DDually
 
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Quote:
Originally Posted by RacinDuallie View Post
Converter or flexplate bolt backing out?
I'm going to pull the inspection cover and check this as well. Never know.
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1995 Cummins with almost no matching paint, 2 dents

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Old 04-11-2018, 05:17 PM   #7
DDually
 
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Quote:
Originally Posted by RacinDuallie View Post
Converter or flexplate bolt backing out?
All the flex plate bolts are tight
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