Duramax Diesels Forum Truck of the Week
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Old 07-29-2014, 05:19 PM
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Default LML CP4 Problems

I did some searching and found some information on this but did not find a thread dedicated to this subject. I have heard claims of failed CP4s wreaking havoc on the entire fuel system. Basically I am wondering the following:

-How exaggerated are these claims? does anyone have any firsthand experience with this happening or know of anyone who has experienced this issue.
-What causes this issue. I have heard that the current ultra low sulfur diesel has a lubricity which is lower than what is recommended by Bosch to run through their CP4 pump, is this true?
-What can be done to rectify this problem? (Lift pump, aux. filter, additive etc.)

Since I'm in the market for an LML I'm just starting to do some research on these trucks, this is the only thing I saw which really stood out at me.
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Old 07-29-2014, 05:42 PM
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only thing that can be fixed with that issue is swapping in a CP3 kit. IIRC I think Fleece has converted one, not sure. As far as first hand experience, I have none, but on duramax forum, there is 5-7 guys that have posted about their failed engines.
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Old 07-29-2014, 05:46 PM
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I wonder if they were stock trucks or tuned? In other words does a tune starve the CP4 and worsen the issue?
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Old 07-29-2014, 05:49 PM
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I believe it has something to do with what the plungers inside the pump are made of.

The ceramic plungers inside the injection pump of one of our 450ISX Cummins exploded and took out the whole motor.
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Old 07-29-2014, 06:08 PM
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We've had a few trucks with cp4 failures and have ended up replacing the entire fuel system. Trucks are 100% stock. Iirc it's due to the ceramic plungers as Dirtymaxx already said. I know fleece and maybe also wehrli make a cp3 conversion kit.
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Old 07-29-2014, 06:17 PM
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We've seen it go both ways. One bone stock Duramax got by with just a new pump. The other two I remember were 6.7 Powerstrokes and they had to have complete systems done.
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Old 07-29-2014, 06:20 PM
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It definitely is the ceramic parts that cause the catastrophic failures of the system.
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Old 07-29-2014, 07:29 PM
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Over 50k on ours still going strong no issues. One trip towing heavy with it you will be in love. All trucks have there issues, and I feel the cp4 claims are exaggerated, you only hear about people posting the bad stuff, no one posts about about thousands of trouble free miles
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Old 07-29-2014, 07:52 PM
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I replaced a friend of mines entire fuel system because of the cp4. It had a little over 100k on it and out of warranty. I tore the pump apart and saw the bores were all scarred up and one plunger wouldn't even move. The rollers on the bottom of t!he plungers had complete flat spots in them to where they wouldn't even ride on the cp4 cam right. Junk Pumps period!
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Old 05-16-2015, 05:40 PM
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Put me on the list. I've got a 2015 with 17k and the pump went out 1000 miles from home. All stock. Needs a whole new fuel system. Dealer said it could be two weeks. Not happy.
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Old 10-21-2015, 07:12 AM
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Quote:
Originally Posted by gmac32 View Post
I replaced a friend of mines entire fuel system because of the cp4. It had a little over 100k on it and out of warranty. I tore the pump apart and saw the bores were all scarred up and one plunger wouldn't even move. The rollers on the bottom of t!he plungers had complete flat spots in them to where they wouldn't even ride on the cp4 cam right. Junk Pumps period!
How many miles out of warranty was it?

Does the cab have to come off to replace it?
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Old 10-21-2015, 11:09 AM
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Quote:
Originally Posted by duratothemax View Post
How many miles out of warranty was it?

Does the cab have to come off to replace it?
don't need to lift cab. we do conversions weekly here in just 3-5 hours (on Already EGR deleted trucks) with EGR your talking closer to 10-12 hrs
all failures we've seen have been related to poor fuel quality/contamination. once they fail is what really gets expensive. 9 times of out 10 requires all new injectors, rail sensor, DRV Valve, Return line assembly with check valve, drop tank to clean, and clean all other fuel lines.
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Old 10-21-2015, 11:24 AM
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Quote:
Originally Posted by quadracer37 View Post
don't need to lift cab. we do conversions weekly here in just 3-5 hours (on Already EGR deleted trucks) with EGR your talking closer to 10-12 hrs
all failures we've seen have been related to poor fuel quality/contamination. once they fail is what really gets expensive. 9 times of out 10 requires all new injectors, rail sensor, DRV Valve, Return line assembly with check valve, drop tank to clean, and clean all other fuel lines.
Hmmmm...so I guess I should invest in an Airdog or Fass.

Like I said, I really do NOT care about performance on this truck. Its just for testing new products, and because all I want is to have a nice new(er), quiet, non-smelly, smooth, comfortable and RELIABLE daily driver...
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Old 10-21-2015, 11:37 AM
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Quote:
Originally Posted by duratothemax View Post
Hmmmm...so I guess I should invest in an Airdog or Fass.
yes strongly recommended. additive never hurts either considering failures stem from lubricity & contamination 98% of the time.
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Old 05-16-2015, 06:46 PM
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Dam it.. I thought gm fixed that issuse...
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