Duramax Diesels Forum Truck of the Week
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Old 11-11-2017, 08:30 PM
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Default Rail pressure is more then 3k lower and no code

My rail pressure at wot is 66mpa desired is 174 mpa I don't get a code and truck is way down on power it has new fuel filters and a 175gph lift pump set at 14psi at idle it drops to around 11-12 at wot any help would be great
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Old 11-11-2017, 09:15 PM
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Could be injectors, CP3 pump, or fprv.

My bet is injectors.


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Old 11-11-2017, 09:19 PM
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[QUOTE=IOWA LLY;1085273]Could be injectors, CP3 pump, or fprv.

My bet is injectors.



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Old 11-13-2017, 06:33 AM
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The last lb7 I fixed it was the pump. But it would set the code. Only on the owner, though. I apparently couldnt drive it hard enough to set it but I could see it struggling on the scan tool

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Old 11-13-2017, 08:10 AM
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Doing a return rate test on your injectors will show you if your problem is injectors or a Pump.
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Old 11-13-2017, 10:30 AM
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Mine was a cp3. 02 OS's don't tend to code for low rail pressure in my experience. I had desired up around 25K, but could only hold 13K on mine when my cp3 went. Thought for certain it was injectors, but they didn't return 10ml on a return rate test, same was not said for my cp3's return.
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Old 11-13-2017, 07:38 PM
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I hope it's the pump but still need to do more testing. I did the return test I pulled the return line off at the tank and disabled my lift pump and cranked for 15secs and only got a few drips of fuel which didn't seem right should it return more then a few drips? Also how do I do just a cp3 return test
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Old 11-14-2017, 12:43 PM
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My 2002 wouldn't set a low rail code until it was down below 10k rail pressure at WOT. I replaced the FPRV with a race valve, and replaced the CP3 and my problem was fixed. It could also be caused by high injector return rates as others have said.
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Old 11-14-2017, 07:25 PM
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mine was pump related , and I experienced the same issues with rail pressure
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Old 11-14-2017, 07:53 PM
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went to do a return test but the cp3 will not draw fuel I thought the lift pump was keeping it from sucking fuel so I pulled the inlet line off the fuel filter housing and ran it to a 2.5gallon jug of diesel and primed it tell j was blue in the face and it just keep going out the return line so I cranked the piss out of the truck and it wouldn't suck anymore fuel out of the jug then the primer would so I tried to start it and it won't start if I hook the lift pump back up the truck starts I'm at a loss
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2002 Idaho robs built trans tunes,suncoast converter/trans,downpipe,5" exhaust ,3500 springs, dmaxstore motor mounts,gauges,lift pump,tank sump,intake heater delete,ppe cooler/ppe deep pan,lift keys alot of cutting and 35"tires
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