Help: Rail Pressure...No really

[adrenaholc1]

So this has probably been asked hundreds of times, but seriously:roflmao:. Why does peak rail pressure (rp) vary from time to time? My scenario on a few occasions has been logs show great rp (around 23-25k) when I do a few boost launch runs on the street up to 90mph or so. Next day I go to the strip and logs show rp at 19-21k and get P0087 every pass. Also happened on the dyno so i changed the ff on the ad2 while on the dyno...no help. However 2 days later with no changes logs looked great. Last night I went a best of [email protected] with 19-20k rp. I don't think it can be any faster without gaining mph...if that makes sense. In other words only thing keeping me out of the 12's is this fuel issue. Am I wasting my time with this problem or should I be looking at other parameters for fueling issues? I'm not a tuner in any way, but I'll log the hell out of the truck to see what might help it et quicker:thumb:. Any help or advice about this would be greatly appreciated...I hope this is in the right section

 

[adrenaholc1]

Guess the only answer anyone has is get a new cp3

 

[Chevy1925]

your fuel pressure regulator may be sticking.

 

[adrenaholc1]

If I've read correctly that can't be logged yet. my next step is to get a temporary guage hooked into the fuel line to monitor supply pressure to the cp3. It will connect to the factory test port via adapter I had laying around from an old 4.3 cpi gasser. It threads on where the test port was originally. I've read about some having trouble with lift pump pressure dropping to 0 at wot this can't be good.

 

[adrenaholc1]

how much stuff has to be removed to get reg. off the cp3?

 

[DIESELMAFIAPER.LB7]

not to much just wring harness and coolant line that goes into the thermostat housing on lly-up maybe the the y bridge been awhile since i tor one off a lly :spit: but i would take your air dog spring out an strech it a bit shuld help up the pressure some thats proabaly were your losing rail

 

[adrenaholc1]

Cool thanks. Whats psi at idle will cp3 handle?

 

[Chevy1925]

Cool thanks. Whats psi at idle will cp3 handle?

Ive seen guys with 45psi up to it with no issue but they have bypassed the FCIM from cooling it with fuel. some say at 12psi or more, the truck will lope from too much pressure at the FCIM. i was runnin 15psi without issue

 

[Devon]

I'm having the same problem with low fuel rail pressure. Bought a brand new cp3 and will be putting it on tomorow. Not looking forward to it but I'm dedicating the whole day to it. I also can only manage a 13.010 @100.92 with 19-21k of RP. Tried tweaking the tuning and went as far as trying someone else's dsp tunes. Did the fuel filters,installed rail fitting, switched from a fprv to race valve,cranked airdog up.replaced a high balance rate injector.so my last resort is the cp3 and reg....then time for some 12 second passes with a good mph 104-106 hopefully


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[adrenaholc1]

I'm having the same problem with low fuel rail pressure. Bought a brand new cp3 and will be putting it on tomorow. Not looking forward to it but I'm dedicating the whole day to it. I also can only manage a 13.010 @100.92 with 19-21k of RP. Tried tweaking the tuning and went as far as trying someone else's dsp tunes. Did the fuel filters,installed rail fitting, switched from a fprv to race valve,cranked airdog up.replaced a high balance rate injector.so my last resort is the cp3 and reg....then time for some 12 second passes with a good mph 104-106 hopefully


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Which pump did you go with?Hope it fixes this terrible problem. Good luck, take pics and share your tips when you complete your install. There are a lot of members on here and other forums with this issue and I'm sure a new cp3 would take care of most of them, however no one really says that their low rp is intermitten like mine.

 

[adrenaholc1]

Ive seen guys with 45psi up to it with no issue but they have bypassed the FCIM from cooling it with fuel. some say at 12psi or more, the truck will lope from too much pressure at the FCIM. i was runnin 15psi without issue

Where is the fcim located? Do LBZ's have these?

 

[adrenaholc1]

If my lift pump checks out ok I've considered getting the Revo kit from WICKED. I figure I'll put the suspect cp3 out in the open where it can be easily accessed, overdrive it to try and squeeze a little more out of it and possibly try to modify the regulator. If that don't work or I screw it up up to bad I'll throw the arson kit at it. And if all else fails new pump:thumb:. Anyone have experience with the revo?

 

[SmokeShow]

There isn't an external FICM that is liquid cooled on the LBZ (or 06 lly like yours) like it is on the LB7, it's incorporated into the ECM. :thumb:

 

[x MadMAX DIESEL]

lbz has it built into the ecm. I'd say get a new regulator first, than if that doesnt fix it you can order a cp3 minus the regulator. I'm ordering a whole cp3 this week. My best was a 12.8 at 102 or 101, but I usually run 13 flat at 99-100

 

[adrenaholc1]

If my lift pump checks out ok I've considered getting the Revo kit from WICKED. I figure I'll put the suspect cp3 out in the open where it can be easily accessed, overdrive it to try and squeeze a little more out of it and possibly try to modify the regulator. If that don't work or I screw it up up to bad I'll throw the arson kit at it. And if all else fails new pump:thumb:. Anyone have experience with the revo?

I knew it sounded to easy as the REVO kit is only for cummins . Damn.

How much work would it be to delete the pump in the valley and run a single belt drive pump?

 

[Dozerboy]

I had the occasional PR problem before adding a lift pump. Where I couldn't hold RP even on small tunes on my first WOT of the day. So as long as went WOT once before hand it would hold fine. I haven't checked it since adding a lift pump.

 

[adrenaholc1]

I'm really starting to suspect a cp3 supply issue. I need to find time to get a fuel pressure gauge set up to monitor. It has 9.5psi at idle and the adj. Reg. On the air dog doesn't seem to effect the pressure at idle. Can these lift pumps supply 15psi under wot?

 

[Devon]

I just bought a stock pump,the old pump is about ready to pull out of the valley, just diddling my thumbs on if I can pull this bad boy out with the Y bridge still intact..I will take some pics of everything removed tomorow as I have to work 2nd shit today. Also debating on getting the arson kit shipped while this things out. I do not plan on building my motor any time soon, and know a lbz cp3 can support decent hp even with a bigger turbo and maybe some 30 overs for a while. Then I'll look for something to add on for a dual kit.right now it's hard enough to get into the 12s due to this low fp bullshit


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[adrenaholc1]

Devon you might as well get the arson kit on it while it's out. I like doing things once and knowing that it will be good to for a while especially if it is something that takes 8 hours, a flashlight, a mirror, 12 busted knuckles, special made tools, and a pack a cig's to calm the nerves to complete. I havn't heard how much power a healthy lbz pump w/arson will support, but my guess would be in the 600-650 range depending on the rest of the fuel system.:thumb:

 

[Devon]

Yea I may order it


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