Fuel pressure too high? - MustangForums.com


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Old 07-04-2005, 04:27 PM   #1  
jhogan2424
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Default Fuel pressure too high?

Another question on fuel pressure.... My fuel pressure guage reads correct at idle, somewhere between 41 and 43 most of the time. But when the car is under boost at high rpm's the guage pegs at 90psi. Is that normal? The car is running extremely well but it is difinetly burning a little rich... Lots of black smoke when i get on it hard. I am running an aeromotive fuel pressure regulator with the vacuum that should raise the fuel pressure under boost but is that too much?
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Old 07-04-2005, 08:13 PM   #2  
stanglx2002
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Default RE: Fuel pressure too high?

you should have the fuel pressure at 40 at WOT so set the psi with the vaccum off
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Old 07-04-2005, 09:32 PM   #3  
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Default RE: Fuel pressure too high?

Ok, I pulled the vacuum off the regulator and capped it off. The fuel pressure still pegs out at WOT. What the hell? Should it stay a constant 40-42 throughout the run?
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Old 07-04-2005, 10:27 PM   #4  
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Default RE: Fuel pressure too high?

do you have a FMU with supercharger they will run the press up so the motor gets the extra fuel it needs so you can still run small injectors.and it only spikes the press. when on boost.
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Old 07-04-2005, 10:46 PM   #5  
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Default RE: Fuel pressure too high?

you take the vaccum off and unscrew the bolt a little to lower the psi
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Old 07-04-2005, 11:08 PM   #6  
jhogan2424
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Default RE: Fuel pressure too high?

Yes, I have a FMU. Is that what causes the pressure to run up to 90 psi? Should I get rid of the FMU and just use the vacuum on the fuel pressure regulator?
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Old 07-04-2005, 11:22 PM   #7  
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Default RE: Fuel pressure too high?

you need to adjust the AFPR
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Old 07-05-2005, 12:42 AM   #8  
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Default RE: Fuel pressure too high?

most FMUs are adj.and you can back them off look on top of it. our old procharger FMU had a very small **** on top that you bled off the boost press. and it would not fully block the fuel return line and would not spike the press as high. As far as not running a FMU that depends on how much HP you are making and how big the injector you are running.also is the fuel prees. reg. that you have boost sensitive if it is you could lose the FMU if its not I would stay with the FMU and just tune with it.If you choose to lose the FMU be very careful not to spark knock the motor or get it to lean.If you get lucky you will just blow head gaskets.Remember you are not playing with a N/A motor you are boosting it and adding lots more air and you got to have the fuel to go with that air or you are gone to screw things up and fast.if you are not real good with boosted motors or understand them very well you need to find some to help you that does have a understanding. JUST MY .02
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Old 07-05-2005, 03:03 AM   #9  
jhogan2424
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Default RE: Fuel pressure too high?

Thanks for the info on the FMU. I'll check it out tomorrow and see if it has an adjustment. If it does, what should I adjust it to? What should the fuel pressure be at WOT and full boost? Should I just leave it running rich to be safe?
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Old 07-05-2005, 09:03 AM   #10  
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Default RE: Fuel pressure too high?

What size injectors do you have?
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