has anyone here ever have a problem with their fmu? if so explain the problem and how you fixed it. is there any way you can check to see if it is working right?

 

I used to have this problem:
FMU got stuck and after boosting, it still controls the fuel return. So I was rolling at 2500rpm, 70mph with 70psi of fuel p.

solution :

how to check to see if it works : fuel pressure gauge, in-cabin gauge preferred.

 

mine straight up failed... not sure why... diaphgrams were intact - it just died...


also.... as far as a/f goes through the band... it's ridiculous - i was running 8:1ish down low, and all the way up to 14-15:1 up top... with random dips here and there

 

I hope that wasn't the Cartech I am picking up tommorrow

 

yeah.... i figured i'd make it look like you broke it.... so much for being sneaky.

 

The problem with Vortech non-adjustable FMU's (for higher boost levels) is that at lower rpm's they increase fuel pressure at the same time that the ecu is increasing injector duty cycle to accomodate the extra air flow that the maf is sensing. Since the ecu doesn't know that the fuel pressure is anything but 43 psi, you end up overly rich until the injectors get maxed out (which is when you need the extra fuel pressure). Then the afr suddenly goes lean because the FMU is now not providing enough fuel pressure and the ecu can't help out anymore. That is why an SAFC is needed along with an FMU to get the afr nice and level. If you have the Vortech S-FMU or the Cartech adjustable FMU, you're okay without the SAFC.