LS1-450

iTrader: (33)

My 99 LS1 engine has a returnless fuel system. Can someone explain how the Procharger FMU works on a returnless system? Boost closes the return line flow which in turn increases fuel pressure. So, how does the FMU keep fuel from returning to the tank on a returnless system? What am I missing?

kp

iTrader: (34)

The ATI setup gives you a braided return line to add to the car and an adapter to go by the fuel filter to hook it in. It pinches off the return pre-regulator. The very first kit I bought, one of the first ATI LS1 F-body kits, had the FMU and an inline boost pump (some kind of bosch pump). After having little luck with the FMU I swapped to 38lb injectors/MAFT (LS1 edit didnt exist at the time) and was able to get the car to run pretty well. Best ET/mph with the FMU was 11.7 @ 109 and with the bigger injectors/MAFT tuning it ran 11.30s @ 120 - wasnt bad for 2001

Anyhow, avoid using the FMU over 5psi, plenty of good tuning solutions out there these days.

EPP

iTrader: (22)

I agree with KP, don't waste your time with an FMU. Larger SVO 42 lb fuel injectors, combined with a larger fuel pump and a good tune is the best way to go for your Miata. Bob

618HAWK

iTrader: (361)

Hear,,,, Hear Dump the FMU. Asking for problems.

LS1-450

iTrader: (33)

Thanks guys,
I had found a re-built Procharger head unit & was looking into fueling options. Found the FMU set-up on their web site & wondered about it. Am trying to avoid installing injectors because of already doing it once before to fuel the head/cam. Will probably wait until the 4L60E goes out before doing anything & then install the head unit w/ injectors & a new transmission. Thanks again for the information.