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 05-16-2015, 06:46 PM
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Dam it.. I thought gm fixed that issuse...
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Old 05-16-2015, 08:25 PM
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Why did they go to a CP4? Is it just bigger? Every time I read about this it makes me nervous about my inlaws LML that I tuned.
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Old 10-20-2015, 07:41 PM
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My 2012 took a dump on me, going 80 mph down the interstate in Wyoming, with 77,000 miles on it. (H&S Street Tune, FASS lift pump, cold air induction and 4" exhaust) A big shudder, dash flashed "Change Fuel Filter" then "Engine Power Reduced". Coasted to the exit ramp (fortunately it was MY exit!) that's when I realized the truck had completely shut down because I didn't have power steering anymore. Threw 7 codes, the first of which was Low fuel rail pressure. Most of the rest had to do with the truck having shut down and still moving faster than the CPU thought it should be moving. FASS filters had metal shavings in them. Factory filter had metal shavings in it. Still wouldn't start. Put it on a hook and took it to a diesel shop. Bottom line - they told me there is a service bulletin from GM on it. And the whole fuel system has to be replaced. (I have a copy of part of the bulletin where it mentions having to replace the whole fuel system if metal shavings are found.) So I'll have new everything, rails, injectors, pump, fuel lines, high pressure lines, etc. I asked the mechanic specifically and he said I have a CP3, not a CP4. That was a bit confusing because I'd been told by others that the 2012's all have CP4s. It's gonna cost me plenty to have it fixed. I didn't find out about the service bulletin until it was well into the tear-it-apart stages trying to find what all was damaged when the pump went out so don't know if I'll have a chance at getting anything back from GM for the repairs. Up until this happened, the truck was running like a champ. No rough running, missing, sluggishness or anything. Just WHAM and done! Can't wait to get it back. Should be done Thursday!
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  #14  
Old 10-20-2015, 08:10 PM
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Quote:
Originally Posted by islandgirl62 View Post
My 2012 took a dump on me, going 80 mph down the interstate in Wyoming, with 77,000 miles on it. (H&S Street Tune, FASS lift pump, cold air induction and 4" exhaust) A big shudder, dash flashed "Change Fuel Filter" then "Engine Power Reduced". Coasted to the exit ramp (fortunately it was MY exit!) that's when I realized the truck had completely shut down because I didn't have power steering anymore. Threw 7 codes, the first of which was Low fuel rail pressure. Most of the rest had to do with the truck having shut down and still moving faster than the CPU thought it should be moving. FASS filters had metal shavings in them. Factory filter had metal shavings in it. Still wouldn't start. Put it on a hook and took it to a diesel shop. Bottom line - they told me there is a service bulletin from GM on it. And the whole fuel system has to be replaced. (I have a copy of part of the bulletin where it mentions having to replace the whole fuel system if metal shavings are found.) So I'll have new everything, rails, injectors, pump, fuel lines, high pressure lines, etc. I asked the mechanic specifically and he said I have a CP3, not a CP4. That was a bit confusing because I'd been told by others that the 2012's all have CP4s. It's gonna cost me plenty to have it fixed. I didn't find out about the service bulletin until it was well into the tear-it-apart stages trying to find what all was damaged when the pump went out so don't know if I'll have a chance at getting anything back from GM for the repairs. Up until this happened, the truck was running like a champ. No rough running, missing, sluggishness or anything. Just WHAM and done! Can't wait to get it back. Should be done Thursday!
That's terrible luck man I hate to hear that. Unless you swapped out the cp4 the mechanic is wrong. I would not go back with a cp4, there are cp3 conversion kits available for relatively cheap.
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  #15  
Old 10-21-2015, 07:00 AM
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106,000 miles on mine...has anyone done any studies regarding additive, if it helps at all?

I dont have time/money to dick with a CP3 conversion right now...maybe this coming spring. I could care less about performance, I just want it to be reliable.
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