What should FP be?
Melting Slicks
Joined: Aug 2003
Posts: 3,399
Likes: 394
From: Lakeville MI
Without an FMU, you should see fuel pressure equal to your no vacuum fuel pressure reading + 8 psi on the gauge.
The effective fuel pressure however, is still only equal to the no vacuum fuel pressure since the gauge is meauring relative to atmosphere and not relative to the manifold pressure.
With an FMU it depends on the FMU step up ratio and fuel pump relief.
The effective fuel pressure however, is still only equal to the no vacuum fuel pressure since the gauge is meauring relative to atmosphere and not relative to the manifold pressure.
With an FMU it depends on the FMU step up ratio and fuel pump relief.
Burning Brakes
Joined: Sep 2006
Posts: 1,142
Likes: 0
From: Spring Grove Illinois
Raid...I just read last night that the min fuel pressure with an FMU you should run is 8:1 @ WOT..Really depends on your A/F ratio I would think...I'm gonna play with my Innovate today to nail mine down..After I fix an oil leak(Damn PVC valve..The oil cooler is leaking)
Last edited by Happydad; Dec 18, 2007 at 06:54 AM.
Thread Starter
Melting Slicks
Joined: Oct 2001
Posts: 2,315
Likes: 110
From: Brandon Fl
Well I was going to eliminate the FMU because ATI recommended to run 42# injectors and no FMU but now that I have done that my pressure stays solid at 43#'s and that is not comforting as when I had the FMU hooked up it would bounce up to 80#'s. I have not hammered on it for fear of leaning the motor and burning something up. I guess I'll spend more money on braided line and hook the FMU back up.
On another note I want to go to a colder than the stock plug to help eliminate the chance of detonation, any recommendations?
On another note I want to go to a colder than the stock plug to help eliminate the chance of detonation, any recommendations?
Melting Slicks
Joined: Aug 2003
Posts: 3,399
Likes: 394
From: Lakeville MI
Is your chip tuned for the 42s, 23s or something else?
Do you also have extra enrichment tuned into the PE tables to compensate for MAF saturation or was all the enrichment coming from the fmu?
Assuming you had 23 # injectors before at 85 psi with the fmu, they would have flowed like 32 # injectors at 43.5 psi.
42# injectors at 43.5 psi should be much richer than 23# injectors at 85 psi. They will likely be too rich, especially at part throttle without some compenstation in the chip for the increased injector size.
Do you also have extra enrichment tuned into the PE tables to compensate for MAF saturation or was all the enrichment coming from the fmu?
Assuming you had 23 # injectors before at 85 psi with the fmu, they would have flowed like 32 # injectors at 43.5 psi.
42# injectors at 43.5 psi should be much richer than 23# injectors at 85 psi. They will likely be too rich, especially at part throttle without some compenstation in the chip for the increased injector size.
Melting Slicks
Joined: Jul 2004
Posts: 3,277
Likes: 32
From: Mission Viejo California
If they only made a global fuel adjustment, you may want it redone to include fuel enrichmnt and timing retard. You need to get the fuel to rise at a 1:1 ratio minimum or you're going to lean out into boost unless you have a way to enrich via the chip. I don't know the answer to this question, but is there a way to get the fmu to work at a 1:1 ratio or even like a 2 to 1 ratio?
Thread Starter
Melting Slicks
Joined: Oct 2001
Posts: 2,315
Likes: 110
From: Brandon Fl
If they only made a global fuel adjustment, you may want it redone to include fuel enrichmnt and timing retard. You need to get the fuel to rise at a 1:1 ratio minimum or you're going to lean out into boost unless you have a way to enrich via the chip. I don't know the answer to this question, but is there a way to get the fmu to work at a 1:1 ratio or even like a 2 to 1 ratio?
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Melting Slicks
Joined: Jul 2004
Posts: 3,277
Likes: 32
From: Mission Viejo California