This is topic Fuel pressure dropping in forum Tech Talk at Northern California Ford Owners  .


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Posted by 91 5.0 (Member # 1527) on :
 
My freind just put an 8-9 psi B&M blower on his 91. We also installed an FMU, 24/lb injectors, Pro-M mass air for the 24's, BBK adjustable FPR, and a 190lph fuel pump. For some reason I wasnt able to adjust the fuel pressure. It stayed constant at about 60 psi at idle with the vaccum tube removed. Under acceleration, the fuel pressure would drop to about 40psi. It almost seems as if the FMU is working backwards. So my questions are...

*Why cant I adjust the fuel pressure?
*Why would the fuel pressure drop under boost instead of raise? (keep in mind the car is bone stock except the mods mentioned above)

Thanks for the help guys.
 

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Posted by 91 5.0 (Member # 1527) on :
 
anyone????
 

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Posted by cheap (Member # 858) on :
 
Damn, what pressure were you trying to set at idle? I thought about 45 psi is what you'd want to start with... how high were you gonna go if it stopped at 60?

It sounds to me like you've got a bad FPR... also, you might have the FMU plumbed wrong. If you have the FMU on the inlet side instead of the outlet side, that could be the cause of your loss of fuel pressure under boost. The FMU restricts more fuel flow on the fuel return side (which makes the fuel pressure go up) the more boost it reads... so if you have it on the inlet side instead of the return side it would restrict the flow of fuel to the engine instead of the flow of fuel back to the tank.

Hell, if Im right on the FMU maybe that's the cause of the whole problem you're experiencing.
 

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Posted by cheap (Member # 858) on :
 
yeah screw the FPR i dont think it's your problem, even though they tend to come bad a lot. Here, look at page 3 in http://www.vortechsuperchargers.com/pdf/manuals/4FA218IM.PDF cause it shows there how the FMU is supposed to be run. If you plumbed it into the intake side instead of the outlet side that would cause the pressure drop.

Dave
 

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Posted by 91 5.0 (Member # 1527) on :
 

quote:

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Originally posted by cheap:
Damn, what pressure were you trying to set at idle? I thought about 45 psi is what you'd want to start with... how high were you gonna go if it stopped at 60?

It sounds to me like you've got a bad FPR... also, you might have the FMU plumbed wrong. If you have the FMU on the inlet side instead of the outlet side, that could be the cause of your loss of fuel pressure under boost. The FMU restricts more fuel flow on the fuel return side (which makes the fuel pressure go up) the more boost it reads... so if you have it on the inlet side instead of the return side it would restrict the flow of fuel to the engine instead of the flow of fuel back to the tank.

Hell, if Im right on the FMU maybe that's the cause of the whole problem you're experiencing.

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