Dropping Fuel Pressure After 24lb Inj/maf Install

Discussion in 'Fox 5.0 Mustang Tech' started by KENS89LX, Jun 3, 2012.

  1. After installing the 24lb setup from 0 throttle to wide open it hesitated so checking the pressure at idle it is at 40lb when you hit the trottle it drops to 20, I have a 110lph fuel pump and a adjustable regulator..Help!!!
  2. Dude, you have run out of pump...Or have a dirty filter or obstructed pressure line coming from the tank...

    Copied from the FORD RACING PERFORMANCE PARTS catalog:


    Fuel Pumps
    The following information is presented assuming the above information has been taken into consideration regarding BSFC, fuel pressure and specific gravity of the fuel being used. Most fuel pumps for electronic fuel injection are rated for flow at 12 volts @ 40 PSI. Most vehicle charging systems operate anywhere from 13.2v to 14.4v. The more voltage you feed a pump, the faster it spins which, obviously, will put out more fuel. Rating a fuel pump at 12 volts then, should offer a fairly conservative fuel flow rating allowing you to safely determine the pump’s ability to supply an adequate amount of fuel for a particular application.

    As previously mentioned, engines actually require a certain WEIGHT of fuel, NOT a certain VOLUME of fuel per horsepower. This can offer a bit of confusion since most fuel pumps are rated by volume, and not by weight. To determine the proper fuel pump required, a few mathematical conversions will need to be performed using the following information. There are 3.785 liters in 1 US Gallon. 1 gallon of gasoline (.72 specific gravity @ 65° F) weighs 6.009 LBS.

    To be certain that the fuel pump is not run to its very limit, which could potentially be dangerous to the engine, multiply the final output of the fuel pump by 0.9 to determine the capacity of the fuel pump at 90% output. This should offer plenty of ‘cushion’ as to the overall “horsepower capacity” of the fuel pump.

    To determine the overall capacity of a fuel pump rated in liters, use the additional following conversions:
    (Liters per Hour) / 3.785 = Gallons
    Multiply by 6.009 = LBS/HR
    Multiply by 0.9 = Capacity at 90%
    Divide by BSFC = Horsepower Capacity
    So for a 110 LPH fuel pump:
    110 / 3.785 = 29.06 Gallons
    29.06 x 6.009 = 174.62 LBS/HR
    174.62 x 0.9 = 157 LBS/HR @ 90% Capacity
    157 / 0.5 = 314 HP safe naturally aspirated “Horsepower Capacity”
    Safe “Horsepower Capacity” @ 40 PSI with 12 Volts
    60 Liter Pump = 95 LB/HR X .9 = 86 LB/HR, Safe for 170 naturally aspirated Horsepower
    88 Liter Pump = 140 LB/HR X .9 = 126 LB/HR, Safe for 250 naturally aspirated Horsepower
    110 Liter Pump = 175 LB/HR X .9 = 157 LB/HR, Safe for 315 naturally aspirated Horsepower
    155 Liter Pump = 246 LB/HR X .9 = 221 LB/HR, Safe for 440 naturally aspirated Horsepower
    190 Liter Pump = 302 LB/HR X .9 = 271 LB/HR, Safe for 540 naturally aspirated Horsepower
    255 Liter Pump = 405 LB/HR X .9 = 364 LB/HR, Safe for 700 naturally aspirated Horsepower

    Note: For forced induction engines, the above power levels will be reduced because as the pressure required by the pump increases, the flow decreases. In order to do proper fuel pump sizing, a fuel pump map is required, which shows flow rate versus delivery pressure.

    That is, a 255 liter per hour pump at 40 PSI may only supply 200 liters per hour at 58 PSI (40 PSI plus 18 lbs of boost). Additionally, if you use a fuel line that is not large enough, this can result in decreased fuel volume due to the pressure drop across the fuel feed line: 255 LPH at the pump may only result in 225 LPH at the fuel rail.
  3. after more investigating, we realized that the pressure was done with the vacuum on, so when we unhooked it I was only carrying 30lbs of pressure so after adjusting it to 40 with vacuum off it runs alot better but I am looking to get a bigger pump...Thanks for the info
  4. Could be, i changed out a failed 190 that I had in mine and used a stock pump to get the car back on the road and its been in there for over a years and I can tell no difference in the way the car runs.