mike89z

Well I got the charger in finally (p600b, 3-core, and 12lb pulley) but it seems like the FMU isnt working . Heres the breakdown:

19" ----- 45psi cruising
14" ----- 50psi idle
0 ----- 60psi part throttle
5# ----- 60psi wot 5000RPM

So the FMU isnt doin its job!! I double checked the FMU connections and they are all goin the right way. Also I took that little restrictor out of the vacuum line goin to the fmu. The screw is turned all the way down and when I blew into the line no air escapes so that seems right. The only thing I can think of is that the FMU is internally screwed up.
I didnt use the inline pump but did put in a wahlbro 340 with a hotwire setup so I would imagine I would be alright to 75psi.
So what do you guys think.....
Has anyone ever come across a bad FMU?

B4Ctom1

open the FMU and check the diaphram if it isnt broken then the lines might be installed backwards

mike89z

Thanks for the info !!

Boxeat2469

Ditch the FMU and switch to speed density pinned for the Sy/Ty 749 setup. I just did it and LOVE IT!! I smoked my best run from last year already, and my new chip is far from dialed in. My O2 voltage at WOT is a nice straigt line when graphed out. All the effort into trying to dial the setup in last year wasn't worth it. Anyone running forced induction should look into the 749 ECM.

Mark A 91Formula

iTrader: (3)

Sounds familiar, couldn't get the FMU for my setup working right either. Tested out just fine using a mity-vac but wouldn't work when hooked to the engine, didn't make sense to me. Switched over to 749, the actual swap is easy. New MAP sensor, change about 10 ecm pins and it's tuning time.

mike89z

I really dont feel like swapping out injectors(superram=PITA) and the theory behind the fmu seems sound. I took my fmu apart and it seems like its missing something(the system was bought used). There seems like there should be a cylinder between the internal plate(boost side) and the fuel diaphram. Any thoughts......

Damon

Might want to just buy a new FMU. Used parts you never know who has monkeyed with them in the past. I've rebult enough carbs to know that almost everyone selling used stuff is doing so because they couldn't get it to work right- and they tried "reengineering" just about everything inisde it to fix it. Often screwing stuff up worse in the process.

I'm no blower genius but I've used enough FMUs to know they basically do their job correctly if working and adjusted correctly.

Damon

Might also want to just double-check the standard fuel delivery system as well. Pop the belt off the blower and unplug the FMU. Make sure fuel pressure is "sane" in a non-boost environment before going after the FMU.

BTW- looks pretty close to me so far. Remember that the stock FP regulator should drop fuel pressure by about 1PSI for every 2" of manifold vacuum. Make sure that relationship holds true in the standard non-boosted operating range. You can even test this on a non-running engine (if you can run the fuel pump constantly) by just supplying vacuum to the fitting on the FP regulator and watching fuel rail pressure.