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Return style wiring HOW TO allowing OE type fuel pump actuation

Discussion in 'How-To' started by MalcolmV8, Jan 27, 2012.

  1. MalcolmV8

    MalcolmV8 Well-Known Member Established Member

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    My return setup has the fuel pumps come on as soon as the key is on and they just stay on but that's kinda ghetto. I'm wanting to get it work like OEM where key on means the pumps prime for a second or two and then go off. Crank the car and pumps are on, engine running pumps are on. If motor were to stall pumps go off after a second or two.

    Anyone figure out how to make that happen? I was thinking of building an electronic circuit to do it. Use one of the outputs from the ECC that's only high when the engine is running to trigger it. If someone else has already done all this though no use in re-inventing the wheel. Thoughts, ideas?

    Thanks
    Malcolm

    EDIT - I figured out the solution towards the end of page 2. Here it is for those searching and finding this thread.

    SOLUTION:
    OK when I first wired up my pumps return style my thought process was to remove the FPDM from the equation as it's no longer needed. Instead I took the DG/YE wire (pin 9) as everyone suggested and used it to power my relay. The downside of course is the pumps run continuously when the key is on regardless of engine running.

    The signal wire from the ECC is the WH/R at the FPDM side (pin 1). It provides the correct times for the pumps to be on such as prime and then off when motor is off. It alone however is to weak to drive a relay.

    So the solution is as simple as using the FPDM output that would normally drive a fuel pump to drive your relay. Use pin 10 & pin 3 to wire your relay. This way the ECC still tells the FPDM when the pumps should be turned on and the FPDM in turn activates your relay.

    Pin 10 = BN/PK (normally fuel pump positive)
    Pin 3 = RD/BK (normally fuel pump negative)

    Note: you must use pin 3 to ground the relay coil (trigger) and not chassis ground or it does not work.

    There you go guys!!
    Malcolm

    EDIT: pinout

    FPDM.jpg
     
    Last edited: Mar 1, 2015
    aarons04cobra likes this.
  2. gt347mustang

    gt347mustang Well-Known Member Established Member

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    I'd like to know also... my pumps run with key on.
     
  3. 03rd SVT

    03rd SVT Member Established Member

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    The thing is that's the way a return style system works. You apply full power to the pumps and regulate pressure via the fuel pressure regulator. If your pumps prime then shut off there is no fuel pressure.

    The pumps prime with the returnless style system because the fuel rail is the stopping point for the fuel until you start the car and the injectors spray. Fuel pressure is regulated by the fuel rail pressure sensor. The FRPS decides how hard the pumps are running.
     
  4. MalcolmV8

    MalcolmV8 Well-Known Member Established Member

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    That's not true. Return pumps have a check valve. When I turn my key to the on position my base pressure is 39 PSI. When I turn the key off it only drops to 30 PSI and holds that. It will slowly bleed out over hours.

    Nope, even factory return fuel systems work the same way from the factory. Turn the key on and they prime and shut off. The check valve in the pump will hold pressure against the fuel rail pressure regulator for a while till you start the car.
     
  5. sn94cobra

    sn94cobra Corn-aholic Established Member

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    I have often thought about figuring this out but haven't taken the time. Mine has been this way for two years. Not as annoying as you think when you get used to it. It is aggravating when you want to load sep tunes
     
  6. GodStang

    GodStang Well-Known Member Established Member

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    On the stock Returnless system you have the PPRV that holds the fuel in the line. It is for starting purposes mostly. Those that have removed the PPRV (or changed hats) sometimes have start issues because there is no longer fuel held in the lines by the PPRV. The FRPS and the FPDM work together with a tune to decide when for the pump(s) to come on. The FPDM is the part that actually sends the signal for it to pulse. When I went to a Fore hat returnless setup I had to add a -8an Check valve back into the system to help with starting issues.

    *EDIT* According to what I could find this is suppose to be controlled by the FPR once it hits the required pressure it is suppose to send a signal to shut off pump or cut power. Wonder if since our Computer is made for returnless does it not know to not shut off or if it is setup wrong in the tune. How is your system setup? I am sure there is a way to do it.
     
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  7. Tims97SVT

    Tims97SVT Active Member Established Member

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    If we go back to fox body days how was the pump controlled? Turn on the key the pump came on for 5 seconds then shut off. Then it came back on when the engine was running. Now did the computer have anything to do with pump control on them?
     
  8. GodStang

    GodStang Well-Known Member Established Member

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    That is what I am trying to find. From what I found those days the FPR would reach its pressure and then send a signal to the pumps to turn off then once the engine started you would be continually running and it would not need to shut off since the car would use the fuel.
     
  9. Tims97SVT

    Tims97SVT Active Member Established Member

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    The fpr could not have sent a signal to the pumps. They had no sensors in the fuel system... I need to go find my fox body chassis wiring book. I'd have an answer for this but I have not gone return yet. Working on it though:beer:
     
  10. cobracide

    cobracide Active Member Established Member

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    - How does a fuel pressure regulator work?
    The fuel pressure regulator is able to maintain proper fuel pressure to the vehicle it has been designed for because inside the regulator housing there is a spring pushing against a diaphragm, the spring pressure has been pre-set by the manufacturer for the desired fuel pressure, so the fuel pump has to pump enough fuel and enough pressure at the same time to overcome the spring pressure.

    Fuel pressure regulator
     
  11. Tims97SVT

    Tims97SVT Active Member Established Member

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    I think we know how a fpr works. We are talking about the prime cycle when you turn the key on..
     
  12. gt347mustang

    gt347mustang Well-Known Member Established Member

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    Wow! This thread is full of nonsense...

    With 10 responses I thought somebody would have had the correct answer by now.

    I'm looking for the correct wire to tap in my wire harness that sends power to the relays for my fuel pumps.
     
  13. Tims97SVT

    Tims97SVT Active Member Established Member

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    Full of nonsense... How so?
     
  14. gt347mustang

    gt347mustang Well-Known Member Established Member

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    ^ because some people think this is controlled by the fuel pressure regulator.

    I was hoping to find an answer, instead i get people explaining how a fuel pressure regulator works.:bash:
     
  15. black 10th vert

    black 10th vert Active Member Established Member

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    That's because the OP, and others are trying to determine how the whole system functions to determine a method of shutting the pumps off once pressurized. You purpose is different, so why bash someone else's thread? If it isn't what you need, or are looking for, just move on. :nonono:
     
  16. Tims97SVT

    Tims97SVT Active Member Established Member

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    Agree!

    Gt347 the answer your looking for to power your relays is simple and can be found via search.
     
  17. MalcolmV8

    MalcolmV8 Well-Known Member Established Member

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    No signal from FPR back in the fox days. I know those very well because I used to put 302 EFI mustang setups in Rangers and wired up many of them. There's a signal from the ECC (I don't have the pin memorized but can get it from my wiring diagrams in the garage) that triggers the fuel relay. So yes the ECC controlled the fuel pump back in the fox and SN95 302 days.

    I don't know if we can make the current ECC in our Cobras simulate that old behavior or not? It's pin 1 at the FPDM which comes from the ECC. If there was a way to reprogram the ECC to simulate the old behavior of return setups that would be great.

    However - the old fox eccs A9L etc. were capable of driving a relay from that pin. The new ECC in our cars only ever had to send a signal to the FPDM so it may very well not be capable of driving a relay. That's why I thought I'd just build a circuit to receive that signal and control a relay myself.
     
  18. MalcolmV8

    MalcolmV8 Well-Known Member Established Member

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    I think it's pin 9 at the FPDM (from memory). It's switched 12 volts when the key is on. Make sure it runs through the inertia switch too if it doesn't it's the wrong wire.
     
  19. SVT GI

    SVT GI Well-Known Member Established Member

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    Green w/yellow stripe on the FPDM harness.


    For the OP, I haven't done this, but seems a HOB switch inline with the regulator would be the answer. Hmmm...have to do some thinking on that one.
     
  20. gt347mustang

    gt347mustang Well-Known Member Established Member

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    Way ahead of you...

    No it cant, hence why I'm posting in here.

    Maybe I'm not being clear enough with my intentions. I want my return fuel setup to behave like a foxbody, or other factory return style cars, not just run pumps full time with the key on like they do now with the green/yellow wire tapped for my relay signal.

    I'm guessing this is what the op is trying to acomplish also?

    From what I'm reading here it looks like there's no such pinout on the returnless style cars.
     

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