so i have been spending the last couple weeks trying to figure out all of the fuel management stuff when doing a supercharger install. reading through as many threads as possible and google searching. i didnt find the info all matched together, but these two links helped.
FPR (fuel pressure regulator) http://www.type2.com/bartnik/reg.htm
FMU (fuel management unit) http://www.superchargersonline.com/content.asp?id=84

after reading a thread that dfownz started about having his Aftermarket FPR stolen and pm'ing him for info, we decided that getting this info all in one place would be really beneficial and clear up alot of questions and headache partially-answered threads.


i got this pic from an FSM for a 5.0 gen. and all info below relates to such but is almost completely cross-gen.

If you are going to install an Aftermarket FPR and a FMU here is what dfownz did.
1.drill a hole through the Stock FPR and run a fuel line from it into an aftermarket FPR (ex: Aeromotive). (**i just thought of this now, but an exact explanation of how/where to drill the hole was not discussed, so dfownz if you could elaborate on what you did exactly that would help)
2.then run a fuel line out of the Aftermarket FPR and into a FMU (ex: Cartech)
3.finally run a fuel line out of the FMU to the fuel tank

reason why it works this way:
-fuel goes into the Fuel Damper, circulates around the fuel rails and goes through the Stock FPR
-the fuel damper regulates the pulsations of the injectors.
-Stock FPR is giving the injectors constant pressure so that even under zero boost, there will be sufficient fuel.
-Aftermarket FPR allows you to adjust your base fuel pressure while the Stock FPR is not adjustable (34psi idle / 43.5psi wot on a 5.0 gen)
-FMU increases fuel pressure based on the amount of boost and is necessary to allow enough fuel to get into the engine when going FI.
-YOU MUST HAVE either your Stock FPR or an Aftermarket FPR initially for there to be any fuel pressure in the rails.
-A FMU CANNOT BE USED without one of these two FPR b/c a FMU does not give any fuel pressure unless there is boost present.

from what i have read (and seen from looking under the hood, but correct me if im wrong and i will edit) there is a vacuum line coming out of the the intake manifold near the firewall on a 5.0 gen and it has a T that shoots a line to the Fuel Damper and the Stock FPR.
-between the T and the intake manifold cut the vacuum line and add another T with a line going to the your aftermarket units
-on the new line add another T to the end with a line going to your Aftermarket FPR and your FMU.

**Useful Links**
Fuel Rail Mod for equal fuel distribution to each engine bank
Return vs. Returnless Fuel Circulation
Fuel pressure: OEM FPR vs OEM FPR + 4:1/6:1/8:1 FMU ratio
another FPR thread
Stock ECU, Z32 MAF, 550's...explained
Fuel management with the Stillen Supercharger kit and Turbo's



if anyone has corrections please post! thanks.

 

34psi (i think) idle / 43.5psi wot

 

http://forums.maxima.org/showthread.php?t=373297


This is my personal favorite fuel related thread.
http://forums.maxima.org/showthread.php?t=288889

In the end, I was at 34psi base fuel pressure with a 3:1 boost curve on my Vortech SMFU. I also had 410cc injectors and a Z32 MAF/A32 ECU combo. Honestly, looking at the chart again, I probably didn't need it at all. I was only pushing 13 psi when I took out the S/C.

The most correction that I had with the SAFC was less than 12%.

 

Great stuff here...Subscribing for more.

 

Good post Steve.

One question I would like answered is what size disc comes in the FMU as part of the stock Stillen kit? I've read 6:1 and 8:1. I've read that Stillen started out with 8:1 and changed to 6:1. What's the final word? Over the weekend, I was just about to take my FMU apart and see for myself, but got distracted with other car projects.

I'm running pig rich and leaving horsepower on the table. (Finally got my Wideband installed) I too, am seeking the ultimate setup. I also have a Z32 Maf, 555 injectors, Walbro and a Vortech SFMU sitting in the garage. Just trying to figure this stuff out too.

Great thread.

 

You probably won't need the SFMU with the 555's.

You could have just gotten the Aeromotive FPR and been done with it.

The stock unit comes with the 8:1, and that's why you're really rich. I swapped mine out to a 4:1 before I installed the SFMU. If I go digging in the garage, I may still have my replacement disc set somewhere, but I have an incling on 1. I sold it or 2. It got lost in the shuffle when I bought my house.

 

By the way, its been a long time since I even though about these formulas. The only reason why I'm looking at it again is because I'm thinking about putting an Xterra roots blower on my 95 5-sp Pathfinder.

 

this thread popped up just in time. I had a few ?s



let me get this straight based of the graph posted abouve about the OEM frp and FMU.

I assume that information is relevant both supercharging and turbo charging?
With the graph above in mind, if a 3.5L motor which its fuel pressure at idle is 51psi, would not need a FMU if it were to boost to say 7lbs correct? it would be fine (for 7psi and under) to keep stock injectors and fuel pressure as is (@ 51psi @ idle)?

 

I would be wary about boost creep. The 7psi is the high end of the boost? Then yes, you would PROBABLY be ok. I'm always one for safety though.


Edit, just do the math for the 51 psi.

Is that without vacuum? What I posted there was without.

 

You're looking at 58 psi on what sized injectors? (again its been a long time)

 

I agree. I would rather side with safety and reliability than anything else.

51psi @ idle with vacuum.
7psi would be the high end of boost, that would be the most boost seen.

It would be better to be cautious in case of a boost spike, cause then not enough fuel could be supplied, engine run very lean, and that could be a bad outcome.

so on the safe side run a 3:1 disk, just to be safe.

I can not remember what the 3.5 injectors are rated at off the top of my head.

 

Could we run 555cc's with Z32 Maf's on stock 4th gen ECU on a 7psi boost level? what tunes? rich? lean? Anyone can confirm? No AFPR and No FMU, nor piggy tunes, just a Walbro pump.

Also, alternatively, for the 7 psi boost with stock injectors and 3.0 engine, what tunes do we get from the 6:1 and 8:1 discs? I heard 8:1 gives a crudely rich result, but what about the 6:1? I'm fixing to buy one of these vortech FMU's. And I'm still confused on which size to get. I'm running the V2-SQ blower with Matty's full starter kit. Also a Walbro 255 lph-hp is in place. And I'm staying at 7 psi's and no other. Anyone can point me out? Appreciate it.

-Peter-

 

^^ This may answer some of your questions...

http://forums.maxima.org/showthread.php?t=459787

 

I disagreed with Mike on that one. I think that if you're going with a "lower" boost setup like you're talking about, the 400-450cc injectors are a better fit all around. It has to deal with the injector pulsewidth and the amount of fuel that is going in at idle. You will have a better idle with the smaller injectors.

I had 410's.

 

well i updated some stuff and added some links to try to cover all the bases.
does someone have the numbers for each gen's stock fuel pressure at idle/wot?