Should I run an FMU or not......

[Cobra R]

I have a 93 Mustang 5.0 with a few bolt ons and an S-trim. I just got it going yesterday and every time I get into boost it spiked the fuel pressure WAY to high...like 100 psi or more. I'm running 24 lb inj and a 190lph fuel pump. i dont know why it's doinf this but I'm going to upgrade to 36lb inj but I was told not to run the FMU. Instead get a boost sensative adjustable fuel pressure regulator and ditch the FMU. BTW I'm pushing about 12 psi. Any opinions on this??

Thanks!!

[Doug]

Dump the FMU and get a set of 36's or 42's. Get a boost sensative fuel pressure regulator and a better fuel pump. You will have plenty of fuel and you will make more power.
Doug

[frdfandc]

I'd sell the 24's, get 42's and be done with it. The 42's have LOTS of room for growth. Also, don't forget your new MAF meter. Get your self an 80mm pro-m calibrated for supercharger application.

[Cobra R]

what I have is a set of 36 lb injetors and a 75mm Pro-M for the 36's and its for supercharged application. I'm gonna ditch the fmu and put them on it and get it tuned this weekend. I have a 1:1 boost sensative pressure regulator on it. I hope it tunes in right.

[Starrman]

My 42's and Pro-M 80mm s/c calibrated rocks!! It gives me a perfect 11.8 a/f up to about 4600rpm, then it richens a bit to 11.5 up to redline, with no additional tuning. This is with a stock fpr and a 255lph high pressure intank pump

[Cobra R]

My 42's and Pro-M 80mm s/c calibrated rocks!! It gives me a perfect 11.8 a/f up to about 4600rpm, then it richens a bit to 11.5 up to redline, with no additional tuning. This is with a stock fpr and a 255lph high pressure intank pump

I put the 36's in there and it ran like ***. It wont idle for **** and it's way too rich at idle and low rpms. The mass air I was using is calibrated for 36's and a supercharger application. I even tried turning the fuel pressure down to like 35psi. What do you guys think about this? I put the 24's back in it for now. I'm babying it and not getting into boost until I figure this out. BTW keep in mind my motor is STOCK. My S trim puts out an average of 10-11psi max right now.

[regattacoupe]

what meter did you use for your 36's? Did you clock the meter at all?

[Cobra R]

what meter did you use for your 36's? Did you clock the meter at all?

I'm using a 75mm pro-M thats for 36's and supercharged application. I didnt try different clocked positions. The sample tube was it about 3:00 though.

[regattacoupe]

are you using a powepipe? try putting the meter as the most inside "track" of the powerpipe.

[Cobra R]

are you using a powepipe? try putting the meter as the most inside "track" of the powerpipe.

No powerpipe. And my mass air is a suck through, not a blow through.

[RACERMO]

i would let the 24's in with the fmu. if your fuel press. is pegged under boost then it's doing it's job. why do you want to switch? is it running lean? if your switching because you thought something was wrong with it, it's not.

[Starrman]

I used to have a idle problem with my old 75mm pro-m bullet. It ran best with the electronics closest to the engine and idled like crap as i rotated it toward the fender, and would eventually die

[Cobra R]

Yeah I decided to put the 24's back in and run an adjustable FMU. It runs pretty good but I think it's maybe sill a little rich. What should be peak fuel pressure under boost? It hits about 80 psi or so at about 10-12psi boost. My new FMU has a lot of adjustment range and it curves the fuel pressure alot better than the stock Vortech unit.

[RACERMO]

I RAN A VORTECH SUPER FMU W/ 12LBS OF BOOST I HAD 100PSI FUEL PRESS.

[midnight]

The formula for computing FP under boost is as folls: Inj size cal X boost# + appx 1/2 of base pressure....So here is the reason that u see 100+...24#=8:1 cal times 11# boost, plus 1/2 base pressure(40)=max load and boost pressure=8:1 X 11=88 + 20#fp=100+..It is not a good idea to run inj's over 80% duty cycle as u can see u r maxed+ out....may lock one/more of them open..