LB7: ppe dual fueler not holding commanded rail

DIESELMAFIAPER.LB7

DIESELMAFIAPER.LB7

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So noticed today i was only.holding 23k rail...im commanding 180 mpa or 26.5k it wont even hit above 24k. Now i have had a regulator code once about a month ago could a bad fpr cause this? Or should i start looking else were like supply pressure?

Forgot to mention i have a II pump in the valley wonder if its a issue
 
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Chevy1925

Chevy1925

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If you pop the plug off one or the other pump aand go run it, will it hold rail then?
 
Subman

Subman

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Mine wouldn't hold either turned out to be a bad relief valve. Started leaking under high pressure. Take a hose clamp or a set of needle nose vice grips and tape the jaws and clamp off the fuel return line. See if it holds rail pressure then.
 
WI Huck

WI Huck

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Subman said:
Mine wouldn't hold either turned out to be a bad relief valve. Started leaking under high pressure. Take a hose clamp or a set of needle nose vice grips and tape the jaws and clamp off the fuel return line. See if it holds rail pressure then.
Click to expand...

Whoa there, that is a lot of pressure you are talking about. :eek: I would not do the vice grip thing. The LB7 has a fuel block where the return is. You can shim that spring inside to raise the pressure relief valve setting. You will find it just in front of the turbo in the valley. It is the part that gets in the way when you try to do a larger intake runner.
 
juddski88

juddski88

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Jul 1, 2008
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I agree that it is most likely a worn FPRV on the junction block. they can get weak even with one stock cp3 and a big tune. shim it or block it and report back. There would be other symptoms if it were injectors.
 
whitelmmmax

whitelmmmax

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I'm fighting the same issue on my lmm. Did the bottle test and all that. Tested my injectors and they had a high return on some of them. Good luck
 
Subman

Subman

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WI Huck said:
Whoa there, that is a lot of pressure you are talking about. :eek: I would not do the vice grip thing. The LB7 has a fuel block where the return is. You can shim that spring inside to raise the pressure relief valve setting. You will find it just in front of the turbo in the valley. It is the part that gets in the way when you try to do a larger intake runner.
Click to expand...

Mine is an LBZ not sure if that makes any difference or not. The new plugs totally block it. Never had a problem doing it and have done it a number of times. You are not talking about much volume here. But I defer to the experts.
 
sweetdiesel

sweetdiesel

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DIESELMAFIAPER.LB7 said:
Just a reg performance code once awhile ago nothing since
Click to expand...

If you have modded or 2 different regulators that could be the reason for the code but doubt that is why its not holding rail

You could pull the belt off and unplug the vally cp3 and see if it can go to 180 mpa

Subman said:
Mine is an LBZ not sure if that makes any difference or not. The new plugs totally block it. Never had a problem doing it and have done it a number of times. You are not talking about much volume here. But I defer to the experts.
Click to expand...

It would be tough on a lb7 because the line that comes off is a pipe that also Ts into the cp3 and/or inj return lines

LLY + you could do as you suggested and I agree about the volume worst case it blows off the hose due to it being clamped....bottle test would be a better way but can be done with the vise grips



my lb7 relief valve has been welded shut for years
 
02dirtymax

02dirtymax

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I would not listen to guys with this in their sig: 06 Chev ec/sb DD SS/11.90 race truck 10.703, @ 130.39 #2

That is entirely too fast. You are better off with a limp dick cp3
 
TrentNell

TrentNell

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DIESELMAFIAPER.LB7 said:
Ya i know i was thinking the stock one is bad going to swap it out. I think i know the answer but can you run a lbz reg an a lb7 reg in a twin cp3 kit? I think its a no but thought id ask
Click to expand...

Yes you can run 2 different regs , it makes it harder to tune but I have done it quite a few times and has never been too bad to get dialed in .
 
DIESELMAFIAPER.LB7

DIESELMAFIAPER.LB7

<----new hotness
Jan 17, 2010
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super diesel said:
I did this a few years back and have had no side effects. I shimed it almost close though. You can also use a high pressure rail end screw to totally block it off as well. This was meant for bleeding off spike pressures sent to the rails. I don't know what the blow off pressure is. He's some picks of the mod. Never noticed any differance with or without it.
#1. is the FPRV (or fuel pressure blowoff valve also).
#2. is a look inside at the hex head screw to be removed.
#3. A look at the guts.
#4. A look down inside at the tine pin hole opening (where the fuel passes).
#5. .120 worth of shim. The slid can move .125 (IIRC).
#6. Is the shim down inside and ready for reassemble.
Click to expand...

isnt the lbz shim that size?
 
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