FMU Question

**ron5.0** · 03-23-2010, 03:21 PM

How can I tell if the Paxton Fmu I have is the one that I can change the disk in
for 8 to 1.
It is silver colored with a red ring that saids Paxton in blue.
I need it to work for 24 lb injectors and don't want to buy the kit to
change it and find out its not the one that can be changed.

Thanks!!!!

**89LX** · 03-24-2010, 09:13 AM

I have a Paxton SN-2000 that will be a year old this June. I run the FMU (mine is all Blue)
with my set up for now, but I opened it up and there is just a slug type piston and the calibration disc and the seal at the bottom and the diaphram at the top and a spring. I would think yours should be adjustable like most. Take the allen head bolts out and look for the disc? Try not to break the diaphram gasket thats all. I was told once I stepped up to a large type injector ie.. 42lb I wouldn't need the FMU any longer anyway. I am building
a brand new motor while we speak so my FMU will be up for sale when I get it done. Hope this helped you out?? 89LX,Todd

**ron5.0** · 03-27-2010, 03:25 PM

Thanks for replying LX89. So yours has a spring in it. I had mine apart and it had no spring in it . I figured that the fuel pressure would act like a spring.
Now I am more confused LOL. Is Your FMU a Paxton unit?

Thanks for your help!!!!

Where are you in CT? I grew up in CT now live in Pa.

**89LX** · 03-27-2010, 06:51 PM

I believe from memory it was above the diaphram on the top side?? My car is in garage in Uncasville,CT. Not here right now so I can't run out and check for you. I lived in Uncasville most of my life.

**89LX** · 03-27-2010, 06:53 PM

sorry, yes it is it came with my new Paxton last June.

**Sponge** · 03-29-2010, 02:20 PM

What's the purpose of t he FMU? Is it a fuel regulator?

**89LX** · 03-30-2010, 08:27 AM

The Fuel Meter Unit helps to move the fuel back in the return side to
the tank. They are calibrated for your injector size for a very good reason.
It is only necessary with the smaller injectors because you need a larger LPH

fuel pump to keep up with the fuel needs of the supercharger.
With the smaller sized injectors they can't use all the fuel that is being fed to them
so it would back up in the rails if you didn't help evacuate the suplus
un-used fuel back to the tank as quickly as possible. This is how it was explained
to me and it makes sense.
I found on a Ford Racing Catalog on Disc for 2009 a handy guide for proper fuel injection
sizes by approximate horsepower ratings, it's on the money for proper fuel air ratios.
You may then tweek your fuel pressure up or down to get the correct "Stoic"
reading on a Wide-band Air fuel gauge. I use an Autometer and it works well, just make
sure to get the Wide-band one and "NOT" the Narrow-band one. You will know the
difference by price the Wide-band is around 260.00 but they are coming down in price
the Narrow band is 50.00 or so and all it will do is bounce back and forth because it is
only designed to read slightly around "Stoic" where as the Wide-band
covers a much larger range. If you want to completely tune your car you can
look into an Anderson PMS system that will do alot more Fine tuning. You can adjust
everything from timing by boost and fuel adjustments by injectors pulses by Percentages etc..