Low rail pressure

[matt2778]

I have a low rail pressure at wot on max effort tune. If cruising at partial throttle rail pressure is at 26k then drops to 22 at wot. Truck is lb7 15% injectors, sportsman cp3, fast 150 lift pump at 8 psi, efi, intake and exhaust

 

[CaptPhil]

22k isn't low. That is about as much drop as you want to see. Some people say you can lose even more rail than that and still make power.

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[S Phinney]

I have a low rail pressure at wot on max effort tune. If cruising at partial throttle rail pressure is at 26k then drops to 22 at wot. Truck is lb7 15% injectors, sportsman cp3, fast 150 lift pump at 8 psi, efi, intake and exhaust

There shouldn't be any low rail with that setup. Stock pump wouldn't be that low. Check for restrictions and lift pump pressures at wot.

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[WVRigrat05]

X2, my LMM on the max effort tune spikes to 27 and hangs out at 25300-26100

 

[matt2778]

There shouldn't be any low rail with that setup. Stock pump wouldn't be that low. Check for restrictions and lift pump pressures at wot.

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Restrictions in the feed to the cp3? What should lift pump pressure be at wot?

 

[WVRigrat05]

I have mine at 15 at idle.

 

[Ne-max]

Restrictions in the feed to the cp3? What should lift pump pressure be at wot?

+1 or more

 

[matt2778]

I have mine at 15 at idle.

I have checked mine and its 8psi at idle. fass has them preset to 8-10 psi. Is that too low? Or is everyone making 500 horsepower with lift pumps set at 8 psi at idle? I just got a new spring that is suppose to increase static pressure to 13-14 psi

 

[WVRigrat05]

My pump is only 100 gph and I run two micron filters, I make it take fuel.

I'd try the larger spring.

Is your fuel pressure relief valve shimmed or plugged?

 

[matt2778]

My pump is only 100 gph and I run two micron filters, I make it take fuel.

I'd try the larger spring.

Is your fuel pressure relief valve shimmed or plugged?

No my pressure relief valve is stock. On 1-4 tunes I hit 26k rail pressure at wot and it will spike to 28k when letting off the gas.

 

[mpeters0991]

That relief valve would be the cheapest and simplest thing to start with.


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[JoshH]

There is not enough information here to make me think there is anything wrong with the truck, and I'm just a little confused how or why anyone is giving advice on fixing what is likely not even a problem.

 

[TheBac]

X2, my LMM on the max effort tune spikes to 27 and hangs out at 25300-26100

LMM to LB7. Not the same. Yours is supposed to be higher. 22000 is NOT low rail, considering LB7 run at ~23,500 normally. Mine used to drop to 21000-20000 at WOT, had to reduce pulse to bring it back up some.

I have mine at 15 at idle.

and you dont lope? 15 thru an LB7 is wayyy to high. FICM might start leaking, and it sure would lope.

There is not enough information here to make me think there is anything wrong with the truck, and I'm just a little confused how or why anyone is giving advice on fixing what is likely not even a problem.

Yep.

 

[mpeters0991]

LMM to LB7. Not the same. Yours is supposed to be higher. 22000 is NOT low rail, considering LB7 run at ~23,500 normally. Mine used to drop to 21000-20000 at WOT, had to reduce pulse to bring it back up some.



Yep.

I forgot the lb7 was lower


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[matt2778]

The problem is there is no noticeable difference between tune 4 and tune 5 max effort
Desired rail pressure says 26k while actual is 21-22k

 

[WVRigrat05]

LMM to LB7. Not the same. Yours is supposed to be higher. 22000 is NOT low rail, considering LB7 run at ~23,500 normally. Mine used to drop to 21000-20000 at WOT, had to reduce pulse to bring it back up some.


and you dont lope? 15 thru an LB7 is wayyy to high. FICM might start leaking, and it sure would lope.


Yep.

My LLY would lope at 20, backed it off to 15 and it was good, LMM doesn't care either.

with a bigger pump and desired r.p. Is 26, I'm ASSuming he has an LBZ reg or the tables set for 26k desired, then it should hold it, for no more shit than he's got with a larger pump.

 

[matt2778]

It's a exergy sportman lbz cp3 with a lb7 regulator

 

[CaptPhil]

We don't know anything about his tune. He could be running a 3200us tune on his 15% overs that could be larger and the pump just can't support it. Can't immediately jump to assuming that hard parts are the problem.

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[Dozerboy]

No one's even going to ask what his PW is before giving advice? What about ported rail fittings or are they stock?

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[JoshH]

My LLY would lope at 20, backed it off to 15 and it was good, LMM doesn't care either.

with a bigger pump and desired r.p. Is 26, I'm ASSuming he has an LBZ reg or the tables set for 26k desired, then it should hold it, for no more shit than he's got with a larger pump.

You don't know anything about how the truck is tuned. If you're running more pulse width than the CP3 can support with the oversized injectors, it won't matter what regulator you are running. I can make stock injectors drop rail pressure if I command enough pulse width.

Matt, this is an issue that needs to be discussed with your tuner. You need to provide logs that show exactly what the truck is doing. You may not have a big difference in power between tune 4 and tune 5. If tune 4 is just on the verge of holding 26k psi, it is probably getting the same amount of fuel in the cylinders as tune 5. Was the tune adjusted for the injectors?