my hemi

Im pulling hair out of my Hair...I have an ATI FMU... just got from procharger a rebuild kit rebuilt and my FUEL pressure still its spiking in boost what am I doing wrong PLEASE help....I swear I have the fuel lines hooked up right I have the FMU going to its own Vac source...I just don't know what else to think....or do.....

Jonesyfxr

iTrader: (2)

I was at SEMA and learned a few things from Aeromotive. They have found you should run the fp reg AFTER the carb, at the return. They have found that placing it on the back side of the rail causes better pressure regulating than on the feed side. They have actually developed sensors to place the fuel bowls and were able to verify this.

Basically, they say to set up the fuel system like an injected car.

Dunno if this will help....good luck.

hillntx

So you have a TPI setup and you're running a Procharger supercharger using an ATI fuel management unit and your concern is that the fuel pressure is spiking when the car is running boost?

To be honest I'm not familiar with any of those systems, but I have a turbo miata so may have some similar experiences.

Are you running stock size injectors or are you running larger injectors to accommodate the increased fuel need under boost?

my hemi

No im running a paxton sn93 the old style ball bearing blower making about 6-7 psi its a 350 tpi 22lb injectors a walbro 255 lph pump..I have a ATI fmu its not working still after the rebuild I just did IT IS not raising the fuel pressure when I go in boost..I cant figure out why its killing me..its a simple device that I cant get working...

ogie

Dont know a lot about your combo , But curious why you are just not using a simple boost referenced regulator? It will give you a 1lb fuel pressure to 1lb of boost raise . It is likely all you will need to do to fix the issue . Aeromotive or Magnafuel sell nice ones.

my hemi

I have a brand new south bay adjustable regulator on it im guessing it is a 1.1 rise type because I had it set at about 52-55 vac off I would drive it and get into boost A/F was only 13 still to lean for me I would like to see at least a high 11 im thinking that's the most I can get out of this regulator I really didn't try to adjust it any higher can it go any higher??? I mean I can try but that's why I went with the FMU figured I could keep the fuel pressure on the stock side increase it while in boost with the FMU...but this damn FMU isn't working and I have no idea why it isn't....

ogie

I am not familiar with the south bay regulator . But I may check where you are picking up your signal at . On my car I have my regulator referenced just behind the throttle plates as that is where you will get the strongest signal . Although your injectors are likely designed to flow at 45 psi people do raise the pressures on them. But usually that is a band aid for having to small of an injector . What I have done to test my system is first check my filters , Then I get a little pancake compressor and regulate the air pressure to whatever psi of boost I will be running . I test my car off as my system is capable of running without the car having to be running . But seeing you are running 6 to 7 pounds of boost you can probably test it with your car running . Have your fuel pressure gauge hooked up and shoot six or seven pounds of air pressure down the reference line and see if you are getting a true 6 or 7 pound rise in fuel pressure . If you are then look at other areas like reference location , dirty injectors , fuel pump etc.

my hemi

That makes sense but I know the fuel pump is fine its brand new walbro 255 lph...also the injectors are not that old...before the FMU I had the fuel pressure set to 52-55 psi vac off idle was around 45 ish...I drove the car around in boost the air fuel would go 13 then that's when this all atarted I bought a used fmu and tried it I put the fuel pressure back to 40ish hooked the FMU up and never saw an increase when in boost I did see it once it went to about 65 psi...then I bought a rebuild kit did that and test drove it the fuel pressure never rose....im lost...

ogie

Dont know if this will help at all.

Sharing a vacuum source may impact the functionality of the FMU and cause inaccurate fuel/air adjustments that may result in poor performance and/or engine damage. Fuel flow through the FMU is specific. If the fuel supply and return line are reversed, this will cause spikes in fuel pressure. A fuel pressure gauge will indicate erratic increases in fuel pressure under boost. The air-bleed valve mounted in its center can identify the top of the FMU. The fuel inlet line should enter the FMU from the side. The outlet or return-line exits the FMU at the bottom in the center.

86Z

iTrader: (4)

your adjustable fuel pressure on the rail has nothing to do with boost, set it 45psi with the line off, after that it only increases slight pressure with vacuum loss.

the fmu blocks the return line and thus increases your fuel pressure, some where your having bleed off in the fuel system where it won't increase, see my pm, send me pics of the fuel lines you have hooked up and the vacuum line.

i assume you have a fuel pressure gauge on the test port of the rail ?