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Electric fuel pump wiring revisited

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  • Electric fuel pump wiring revisited

    found this while searching for the pinout of a VW fuel pump relay:

    http://www.ratwell.com/mirror/sfraser/relay.html

    this is exactly the schematic I was trying to make myself, except someone's already done the homework. Hope this helps someone... if one wanted to include an inertia switch it would be trivial to insert it somewhere in the circuit (possibly between terminal 31 and chassis ground)

    Only thing he didn't give us is the part number for the socket that holds aforementioned relay. I'm working on that...

    nate

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  • #2
    Good page.
    Thanks

    Mike

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    • #3
      Interesting concept, thanks Nate.
      sigpic 1963 Studebaker Avanti: LS1 motor and T-56 transmission have been moved rearward, set up as a two seat coupe with independent rear suspension. Complex solutions for nonexistant problems.

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      • #4
        Part numbers from germansupply.com

        321 906 059 C Fuel Pump Relay w/ Fuse Ear... $CAD 28.00
        849 941 593 Relay Terminal Housing 9-St... $CAD 14.00
        558.6010 Terminal - .110" Non-Insula... $CAD 0.58 (each)
        558.6032 Terminal - .25" Non-Insulat... $CAD 0.75 (each)

        you'll need a special crimp tool for this, the kind used for weatherpack connectors (I have one)

        only thing I have yet to determine is if the relay part number I've referenced includes the carb priming function. I've asked a couple knowledgeable VW-heads and didn't get a definitive answer. I guess I will just have to order the stuff and find out. If it doesn't, I can pull the relay from the Corrado in the garage and see if it will work in the socket referenced above. (I don't think that it will however... bummer)

        If the relay that fits in the available socket will not prime the carb, I may have to go back to the drawing board, and/or simply make my own socket for the relay that works the way that I want it to (BTDT, just takes a little ingenuity and epoxy.)

        nate

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        • #5
          N8, I read the text that accompanies that link, and it would appear that it does not have the carb-priming function. The relay was used with VW's CIS system. You get about 1/2 of fuel pump action after initial turn-on. Then it has to see voltage spikes from the coil primary to reset the internal timer. Nice work on the part of the writer!

          What I'd do, I think, is simply have a standard Bosch relay from Pick 'n' Pull, plus an oil pressure switch, and a hidden manual toggle switch with 3 positions: normal, pump fed by relay; prime/over-ride, pump fed directly through switch; and "off" power to pump disconnected. Simple anti-theft device.

          Once I get that 4.3 engine into the '65 Commander, I will have to do exactly this, as the engine has no provision for a mechanical fuel pump.

          Gord Richmond, within Weasel range of the Alberta Badlands
          Gord Richmond, within Weasel range of the Alberta Badlands

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          • #6
            I know that I've had CIS engined cars that would run the fuel pump for 3-4 seconds after initial turn on then would work as you describe above. The thing is, they were all newer than the cars that use the exact relay discussed; and I have not driven a car that uses the exact relay discussed. I of course could use the relay for, say, an '84 Scirocco and I know it'd work exactly like I want it to, but it uses a different socket which was molded into the entire fuse/relay panel for those cars.

            nate

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            • #7
              All my VW fuel injection books went with the GTI that I sold last Summer. But, I remember some fuel pump relays had the rev limiter function incorporated. There was an upper limit to the number of pulses per min. from the distributor, above which the fuel pump would shut off.
              If the relay you use was intended for a four cylinder engine, and you are using it with an eight; rev limit will be half the intended speed. I would expect about 3K rpm. If it's there, you would see it the first time you try to hold high speed long enough for the fuel in the carb to be used up. This could be dangerous, especially with a supercharger. It runs leaner as the fuel level in the carb drops; instead of sharply cutting off like it would with injection.
              It would be safest to check with a volt meter or test lamp, to see if the rev limit function is there.
              Mike M.

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              • #8
                yes, I plan to test this out before removing the mechanical fuel pump. I don't believe that that was incorporated into any of the cars I've driven however... I know I've floated the valves on my '84 GTI before! (trying to get out of the way of a red light runner while making a left turn... that'll get your juices flowing.)

                nate

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                • #9
                  Now that I think about it, I'm pretty sure the rev limiter was built into the distributor rotor, not the fuel pump relay. Haven't received the parts yet so no way to check though.

                  nate

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                  • #10
                    I remember pictures of the Bosche rotors with the built in rev limiter in books from the '70's. There's no mistaking them!
                    Of course. there are a few ways to limit maximum engine speed. I'm pretty sure one was to build a limit into the fuel pump relay. It is also a maximum speed limiter for the car; as well as the engine.
                    Mike M.

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                    • #11
                      follow up: I've procured all the parts necessary to do this and tested the setup today. Everything works fine, BUT the relay only "primes" the carb for about a second on key on, not the 4-5 seconds that later relays did. I ASSume that I could probably pop the top of the relay and mess with the circuit to increase that time, but if I have let the car sit for a long time I could just cycle the key a couple times. It works fine with the Chrysler ignition, which was my biggest concern. I did not get this installed because I found that I was out of 5/16" rivet nuts which made mounting the fuel pump a little difficult (I was going to put it on the little vertical piece of sheetmetal under the rear seat; pulling the rear seat and having to have a helper inside the car to remove/install the fuel pump bracket seems... inelegant.) other than that I don't see any issues with using this setup. I did have to epoxy a little metal tab onto the relay socket so I can mount it in the car. (I'll screw it up under the dash somewhere - having a tach in the car, I have all the wires that I need right there.)

                      nate

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