i dont know what to do here fuel problems

mch646

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Dec 13, 2011
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I can assure it's not a tuning problem cause the same tunes run great on his tow rig and he just says to buy bigger sticks and a new cp3and don't mess with each part individually which I would do if I had the money but it's not an option for me right now
 

Burn Down

Hotrodder
Sep 14, 2008
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Boise Idaho
Sorry, I checked your thread at lunch today but didn't have time to reply.

I would try a FPR before a cp3... Like Chris said call Dimitri he probably has one laying around you could try. If he doesn't Try calling Trent (EPR). Heck I have one that I would loan you but it will take a week to get to ya. Also I have heard of guys running 2-stroke oil to help free up sticky FPR's for what it's worth... Just the cheap walmart 2 stroke oil nothing fancy.
 

The Neens

BFD
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Aug 10, 2006
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I can assure it's not a tuning problem cause the same tunes run great on his tow rig and he just says to buy bigger sticks and a new cp3and don't mess with each part individually which I would do if I had the money but it's not an option for me right now

Then change the FPR...
 

mch646

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Dec 13, 2011
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Ha I would but pat is helping me with one after a bottle test tomorrow I drove up to dimitri last week for a returned and the dsp5 but this problem was there before these tunes. Anywhoo he is building 3 trucks ATM which I am excited to see this year it will be a nice surprise he's running 2 at drags and has a nice twinned tow rig ha I don't understand how he does it tho and the oil is dummy cause I run that ever 5 tanks or so to help quiet it down. And its OK dude don't worry bout it
 

mch646

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Dec 13, 2011
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OK just an update here y'all changed my fpr with a brand new one and its still the same general symptoms idle Psi is actually higher now and under wot its 12-14k depening on tune so I guess lucky me gets to change the injection pump unless there is something else I am missing ps the port on the passenger side of the engine where you check fuel vacuum that leaks constantly and the lift pump is at 8 psi
 

Sledhead

Mountain Pass Machine
Nov 29, 2008
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I think us LB7 guys should not rule out the Fuel Pressure Relief Valve. Mine won't be stock much longer.
 

mch646

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Dec 13, 2011
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But where I'm hesitant on the relief valve is after i let off the gas fuel pressure spokes up to 23k and I don't know if it would do that if the fprv was bad would it
 

super diesel

<<<< Under Pressure
But where I'm hesitant on the relief valve is after i let off the gas fuel pressure spokes up to 23k and I don't know if it would do that if the fprv was bad would it

Sure it will. It can only bleed off pressure so fast. That means that when the injects stop using the fuel they want, or sharing the fuel with the all the injects and FPRV it ALL goes to the FPRV and sensor on the junction block. The reg on the cp3 can only react so fast to shut down the pressure and all the pressure built up already needs to go some where because the injects arn't using it any more. This is the reason for spikes when the throttle is chopped off the best I can explain it. These have been know to be a problem in the past with draining off precious fuel pressure and I don't suspect the issue will be getting better over time unless there shimmed. May not be the problem or all the problem. But one less thing to go wrong in the future if addressed. This is trouble shooting stages that must be taken to find the root cause. Your eliminating a possibility and it may or may not suddenly cure it.
 

mch646

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Dec 13, 2011
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OK and on lb7 I have been told the fprv is located in the valley and on the drivers side furl rail so which is it
 

super diesel

<<<< Under Pressure
Its in the valley right down in front of the turbo and on top of the air intake Y bridge. The FPRV is pointed at the passenger side fender off of the junction block. some steel lines (return fuel lines) are banjo bolted to the output side of it. This will have to be disconnected to remove it for the mod. Well, you don't have to remove it but it's a bit trickier doing it that way.
 

mch646

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Dec 13, 2011
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The worst part is I just was in there doing the fpr ha back in we go and do you know the bolt thread for the Turbo intake horn I lost one yesterday and that's no Buenos
 

super diesel

<<<< Under Pressure
Try this. While looking under the hood, unhook the FPR and look for any leaks at the injector fittings or at the rail end plugs. Make sure everything is buttoned up good. Did you say you did a bottle test and checked for no fuel in oil? I know you said your injector rates were reasonable, but you need to rule more stuff out to get to the root.
 

mch646

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Dec 13, 2011
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OK ill check that today and no fuel I'm oil and fuel rail psi is at 15k when cold at idle with fpr plugged in
 

mch646

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Dec 13, 2011
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utah
And when warm its at 9 k andi just unplugged the fpr and fuel rail pressure does not do anything and I don't see any leaks at fuel rail ends or injector lines
 
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mch646

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Dec 13, 2011
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utah
It does it in every tune lowest tune is around 60 up a mileage tune and high tune is 250-300 horse tunedoesnt matter what its on