Fuel Pressure on an LBZ [Archive] - Duramax Diesels Forum

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blue68383
02-03-2009, 10:31 PM
How much psi can I turn my 1792 up safely. I recall only being able to run 12 psi on my LLY because of the FICM correct? Since there is no FICM on the LBZ can I run 20? 30? 40? 50? psi?

super diesel
02-03-2009, 10:39 PM
If you have a factory priming pump only about 12psi before it starts to slowly weep (what I've seen anyway). Even if not, the higher pressure will start to make the truck lope at idle (my experiences saw it at about 18psi in low milage trucks). On higher milage trucks 100K+ it is even lower because of the wear in the fuel pressure regulator (unless it's been replaced recently). The fuel pushes past it and causes the lope (high fuel pressure at idle). Hope this helps.

LBZrcks
02-03-2009, 10:52 PM
How much psi can I turn my 1792 up safely. I recall only being able to run 12 psi on my LLY because of the FICM correct? Since there is no FICM on the LBZ can I run 20? 30? 40? 50? psi?

Will it even put out that much?:confused:

I run about 15psi out of my ppe pump

RPM Motorsports
02-03-2009, 10:55 PM
Mine is set at 14-15psi as well. It will pull all the way down to 3psi. durring a pass.

blue68383
02-03-2009, 10:58 PM
If you have a factory priming pump only about 12psi before it starts to slowly weep (what I've seen anyway). Even if not, the higher pressure will start to make the truck lope at idle (my experiences saw it at about 18psi in low milage trucks). On higher milage trucks 100K+ it is even lower because of the wear in the fuel pressure regulator (unless it's been replaced recently). The fuel pushes past it and causes the lope (high fuel pressure at idle). Hope this helps.

What do you mean weep? Is there an aftermarket alternative to the factory priming pump? Can you tune that lope out by decreasing PW at idle?

blue68383
02-03-2009, 11:04 PM
If you have a factory priming pump only about 12psi before it starts to slowly weep (what I've seen anyway). Even if not, the higher pressure will start to make the truck lope at idle (my experiences saw it at about 18psi in low milage trucks). On higher milage trucks 100K+ it is even lower because of the wear in the fuel pressure regulator (unless it's been replaced recently). The fuel pushes past it and causes the lope (high fuel pressure at idle). Hope this helps.

What do you mean weep? Is there an aftermarket alternative to the factory priming pump? Can you tune that lope out by decreasing PW at idle?

blue68383
02-03-2009, 11:07 PM
Mine is set at 14-15psi as well. It will pull all the way down to 3psi. durring a pass.

Why do these pumps lose soo much psi at WOT? Not enough GPH? Or is it pump design?

ripmf666
02-03-2009, 11:10 PM
I'm at 15lbs

NWTDIESEL
02-03-2009, 11:17 PM
What do you mean weep? Is there an aftermarket alternative to the factory priming pump? Can you tune that lope out by decreasing PW at idle?

Weap=leak then drip on the manifold and stink up the engine compartment.:D I took mine all apart and put different screws in the top along with a few other changes i got it to hold a little more psi. 15psi is enough.

LarryJewell
02-04-2009, 05:20 AM
Mines puting out 9 :confused:

LB7Diesel
02-04-2009, 06:50 AM
I turn my edelbrock down to around 10 psi in town, and then crank it up to 15+ at the track. No leaks.

super diesel
02-04-2009, 07:57 AM
What do you mean weep? Is there an aftermarket alternative to the factory priming pump? Can you tune that lope out by decreasing PW at idle?

Yes. Weep=leak. I went to a dual filter down on the frame. One before my pumps (protects the pumps and they last seems like forever) and one after the pumps (protects the CP3 and inject from smaller stuff and from pump wear items). The one before is a 10 mic. for ease of sucking through to the pumps and the one after is a actual 2 mic. that is far better than the factory filter and can handle over 100 psi if needed. I changed my pump set up from what I use to make and sell, however those are fine. I just did it a little different for test purpouses in the new motor. My new set up is a compound style. I have 4-5 psi all the time, then I have a 7psi pump feed them above 8psi (pressure switch). It jumps up to 10-11psi when this happens, but then the duel fueler sucks it down to about 6-7psi on a big run. I use to have a 3 stage that would bump pressure up to about 120 psi on big runs that came on at over 25 psi. This had no effect on how well rail pressure was held for me that I could see. After a year and a half. I changed it.

There no way to tune out the lope. It's fuel being pushed past the regulator that controls the fuel flow into the CP3.

RPM Motorsports
02-04-2009, 07:34 PM
"Why do these pumps lose soo much psi at WOT? Not enough GPH? Or is it pump design?"

Any pump is going to pull down to a certain PSI while in use, Unless it's on a regulator. As long as it is still supplying fuel psi to the pump, it's doing it's job. I have thought about putting a high preasure pump in place, and use a regulator to hold a constant preasure, but I sold my last race pump last year.

LB7Diesel
02-04-2009, 07:51 PM
At WOT your cp3 is cycling alot of fuel to try and keep up to commanded RP. Not saying your using all of it, but it does draw alot. As long as there is positive pressure it's doing it's job by keeping it fed. This is where the big outlet ports and 150GPH come into play.

Some people have luck with 90GPH pumps. My choice would be a 150, but that's just me.

2500HeavyDuty
02-04-2009, 08:17 PM
I'm trying to lower my psi to the cp3, I'm at 12 and its causing my cpe to do funny things

blue68383
02-04-2009, 08:40 PM
I'm trying to lower my psi to the cp3, I'm at 12 and its causing my cpe to do funny things

Whats it doing?

12secondhandshaker
02-04-2009, 08:40 PM
Buy a FASS and be done with it:baby:

I had two 1792's; both leaked and dropped in pressure at WOT. Cant say the FASS got me into the 12's but it didnt hurt my times at the strip thats for sure. Every once in awhile I will get a FPR code CEL but other than that the FASS has been a great pump, not to mention the extra filtration. You get what you pay for thats what I say.

hondarider552
02-04-2009, 09:28 PM
im at 12psi

McRat
02-04-2009, 10:16 PM
There are two ways to address the "lumpy idle" issue with high output lift pumps.

One is to rescale the CP3 amps the other is to lower the rail pressure in problem areas. Both accomplish the same thing, and can be done with EFILive.

2500HeavyDuty
02-04-2009, 10:59 PM
Whats it doing?

itl surge on acceleration and highway speeds.

i did tune out the high rail pressure that was caused by adding the lift pump.

but ima drop it down to 10psi and hoprfully i wont have to make any adjustments to it on efi

super diesel
02-05-2009, 07:57 AM
There are two ways to address the "lumpy idle" issue with high output lift pumps.

One is to rescale the CP3 amps the other is to lower the rail pressure in problem areas. Both accomplish the same thing, and can be done with EFILive.

Pats correct.
This is possible if it's not leaking around the slide (is what I meant). Some times I don't say thing right. I had this situation a few times and had to change the reg to control it (newer LB7 reg). Maybe mine were just to worn out (to much fuel excaping around it instead of going through it like it should).

sweetdiesel
02-05-2009, 08:51 AM
itl surge on acceleration and highway speeds.

i did tune out the high rail pressure that was caused by adding the lift pump.

but ima drop it down to 10psi and hoprfully i wont have to make any adjustments to it on efi


My pumps are on a switch since they are flow through KD pumps
no matter what pressure you use it will effect the cp3.

log rail current in milliamps and you can see this effect.

As Pat said it can be tuned out for the most part. It's more of what YOU can live with:)

2500HeavyDuty
02-05-2009, 10:01 AM
My pumps are on a switch since they are flow through KD pumps
no matter what pressure you use it will effect the cp3.

log rail current in milliamps and you can see this effect.

As Pat said it can be tuned out for the most part. It's more of what YOU can live with:)


i have the amps turned up in the first 3 cells on b1010 about 65ma.

but im trying to lower the pressure to where i wouldnt have to do that since my cp3 is new