Help with my sick LB7 - Diesel Bombers



Chevy/GMC Duramax 01-04 LB7 Discussion of Chevy and GMC Trucks with LB7 Duramax Turbo Diesel Engines

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Old 06-07-2017, 09:18 PM
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Default Help with my sick LB7

Trucks a 2003 lb7, some back ground before we get into it's issue. Truck has the fallowing mods,
custom intake.
Custom ladder bars.
Custom 4in exhaust in front of rear tire.
Custom boost controller on 32 psi.
ATS manifolds and up pipes.
ATS kit in transmission with billet prostar converter.
ATS copilot.
EFI live dsp5.
Yukon locker.
Ported turbo inlet horn.
Wrapped charge pipes.
F1 90 over injectors.
Industrial injection 85 over cp3.
Fass lift pump.

Truck went from running great, with a intermittent fuel prime issue for the last 2.5 years, all of a sudden omw home one night from work I went to pass someone and it fell on its face hard. Anything over 1/2 throttle and it bogs down bad. Blows a slight haze of dark gray/black smoke instead of it's usual coal rolling. Makes me think it's a fuel issue.

Now what I have done. My snap on scanner doesn't give me a actual rail pressure reading, FML... I have not one single code. I thought maybe the fprv was bad and put in a ppe race valve. Made it a tiny bit better but still wayyyyyy hurt. I have no fuel leaks and just put two new filters on after this happened on the FASS. Still have my wix on the stock housing that has 9,000 on it in the last 2.5 years. What data I do get looks good. TPS etc. I'll attach a copy of the cylinder contribution test. Idk what that should look like, not a diesel technician. Don't have a lot of experience with them. No rookie tho as I'm gm certified. Just looking for help, tips etc here. Don't wanna just throw money away as this **** is expensive!!! Thanks ahead of time!
https://goo.gl/photos/ZsyEAbtTUFfhDwdd9

If there is something you wanna see, data videos of truck driving etc. Let me know and I'll get it!
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Old 06-17-2017, 08:32 AM
2500HeavyDuty's Avatar
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if you have efi live why arent you able to monitor fuel rail pressure with that instead? is there any fuel in the oil, the intermittent fuel prime issue seems fishy. ppe doesnt make a race valve for the lb7 as far as i know, you have to shim it yourself (i made a writeup on here)
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Old 06-22-2017, 08:42 AM
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Ppe race valve is installed and fine. Looked the exact same as what goes on a common rail Cummins. I did mess with the truck yesterday as I had to use it to move my tool box to my new job. At times it was idle hunting and surging. It was also surging in drive on the brake and at times would not respond to throttle in anyway and then all of a sudden respond all at once. Now when I got the truck the lift pump wasn't working. Wiring issues. I unplugged the lift pump and truck truck refused to run with out it. It ran with out it when I bought it just fine. I'm going to do a few more things today to confirm but I strongly suspect a weak cp3 now why do these parts gotta cost soo much!!!


Edit: the truck has EFI live dsp5 but I however do not have EFI software or a display to read the rail pressure.

Last edited by 84z28ls1; 06-22-2017 at 08:43 AM. Reason: Forgot stuff
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Old 06-22-2017, 09:29 PM
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Figured I would go ahead and add that the truck will absolutely not run with out the lift pump or me manually priming it the whole time. Regardless of rpm. Witch makes me believe the cp3 is to weak to pull fuel in. Also the truck has been surging and idleing rough like the fpr might be the problem. But that doesn't explain my wot power or past half throttle power issue. For a minute I thought well maybe the fpr stuck in a mid way position were the pressure is too high for idle but not high enough for 1/2 throttle and higher. But that doesn't explain my no run condition with out the assistance of me priming or the lift pump supplying the fuel to the cp3. Truck also jumps rpm at a stop with the brake down and try to power through the brakes. Once again like a fpr but then some of my other symptoms don't match up for a fpr. Truck is getting bad fuel Mileage as well. I am going tomorrow to Barrow my buddy's display pod that shows balance rates and true tail pressure. So I will finally get the awnsers I want!!!!
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Old 06-24-2017, 04:49 PM
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Barrowed my buddy's edge cts2 yesterday and confirmed it was the cp3 pump. Anything over 1/2 throttle it commands 23k but drops down to 5,000 down to 2,500 depending on throttle. Time to buy some parts.
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