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  • Fuel Pump Not Working When Cranking

    Hello y'all!

    I have the Pro Flo 4 kit for my 302 (#35940) as well as the fuel pump kit #3604, and it seems that when I'm cranking so start the engine, my fuel pump is not working. It is pumping fine right before and after. I can monitor data when trying to start, and I see the fuel pressure dropping to 0PSI as soon as I try to start the engine, from around 50PSI just before that. While troubleshooting, I found out that two wires of the main relay were somehow badly wired - contacts 30 and 87 were swapped. I'm gonna replace the relay tonight, but from my understanding, it wouldn't make that big of a difference since that only meant that 12V were always at the exit contact. So if it is not the relay, what could cause the fuel pump to stop when cranking? My only two guesses are low voltage, but that would disconnect my ECU from the bluetooth tablet when cranking as well, which is not, or a bad ECU... Could it be so? Any ideas would be appreciated.

    Thanks guys!

  • #2
    30 and 87 are the Normally Open contacts.
    Example in the first diagram I have used for over 40 years : https://www.the12volt.com/doorlocks/...door-locks.asp

    What is the voltage at the fuel pump when cranking the engine?
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    • #3
      Edelbrock inline fuel pump kit #3604 ---Does not require a relay.
      Wire from PF4 ----Orange goes to + on pump / Tan/white goes to - on pump.


      Note: if one were to add a relay here is the pins : PF4 intank pump relay.JPG

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      • #4
        2700 Cast
        I just assumed my pump was wired to the main relay since it is wired this way in the wiring diagram of the PF4 manual (see attachment). I just plugged both connectors together (the one from the fuel pump and the one from the harness). Does this mean the wiring in the manual is wrong? Or it is right, and I should wire it differently?

        @BITE_ME
        I haven't checked the voltage directly on the pump itself while cranking but I will definitely try it tonight!
        Attached Files

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        • #5
          Straightforward wire connections:

          Wire from PF4 (fuel pump connector)----Orange goes to + on pump / Tan/white goes to - on pump.

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          • #6
            2700 Cast's diagram is for "in tank" fuel pumps.

            If yours is mounted on the "rail" then it's fine.

            In tank pumps use a Positive to turn on the pump.....The Opposite of Edelbrocks EFI systems.
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            • #7
              Alright, so I made a few tries tonight. I now think I have two distinct issues: The fuel pump is not working while cranking, and the engine is not starting. I do not think the low fuel pressure is stopping the engine from starting, here's why:

              I looked at the voltage when cranking the engine. It lowers below 12V, I got about 11.3V at the lowest. Could it be that the voltage drops too low for the pump to keep working while cranking? Maybe that's the problem, but I don't why it does so nor how to prevent it from dropping. I then tried to plug the fuel pump directly to the battery and see if it would keep pumping while cranking. It did, and I was able to keep the pressure steady while trying to start the engine. Alas, to no avail, the engine would not start.

              I tried calling Edelbrock tech support but it was right before end of work hours, I'll try again tomorrow. The guy still gave me a few options to look at. I updated my firmware as well as the map. I was at firmware 50 and map 5000, now firmware 65 and map 5000_v65. The coil I installed is a generic one I bought from my local part supplier, with a primary resistance of 1.4Ohm. Any new idea is more than welcome. Thank you!
              Last edited by bilodeaum; 06-04-2020, 08:06 PM.

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              • #8
                Is that 1.4Ohm, or 1.4KOhm?
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                • #9
                  That is 1.4ohm, not kohm.

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                  • #10
                    Run a Hot wire 12v from battery to the positive on the pump & ground the neg.
                    With the pump running constant ----does the engine start & run great ?
                    All Inputs on tablet are with in spec?

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                    • #11
                      I tried it, the engine does not start unfortunately, even with a steady pressure of around 40-50psi.
                      As for the tablet, everything is green and within specs (besides fuel when pump is not working and voltage when I crank for too long). But the voltage gets back up when I let go of the ignition. Battery voltage is around 12.8V when doing nothing.

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                      • #12
                        So it's the PINK/BLACK wire: This wire needs a uninterruptible 12 volts positive connection, that has power when the ignition key is running, and cranking.
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                        • #13
                          Originally posted by BITE_ME View Post
                          So it's the PINK/BLACK wire: This wire needs a uninterruptible 12 volts positive connection, that has power when the ignition key is running, and cranking.
                          Mark,

                          For testing try to jumper the Pink/black wire directly to the battery post. Then try to start engine.

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                          • #14
                            Hello guys!

                            Little update: so I did as 2700 Cast as suggestedand guess what.. it worked! I managed to get it running at idle, adjusted timing until the engine was running smoothyl (tablet was indicating 16°), set idle RPM at 900RPM and and then everything was perfect. Or so I thought...

                            I stopped it to continue working on it the day after. The next day, fefore I tried to crank, I adjusted fuel on cranking and tried to start it, but it would not start. I tried resetting what the ECU had learn but it did nothing. I managed to start it by giving about 20% of throttle, but it was not running great and stopped as soon as I let go of the gas. I could not get it to start again that day.

                            Now, everytime I try to start it, I have to give about 20-30% of throttle. The engine will not stay at 900RPM no matter what I do. And, as soon as I stop with the throttle, the engine stalls and won't start again. I have to wait a couple hours before I can try again to start it, with the same results as before. It is getting frustrating... Any idea what it might me? Another thing that may be worth mentionning, I see the IAC is not at 70%. is normal to be that high? How can I change that value? Any help is appreciated.

                            Thanks!

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                            • #15
                              Could you please post a picture of the "Digital Display". With the key ON, but motor OFF.
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