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Electric fuel pump connection

Discussion in 'Fuel System & Electrics' started by Alpal, Aug 9, 2012.

  1. Alpal

    Alpal Moderator Staff Member

    Messages:
    8,508
    Location:
    Melbourne Bend of Islands
    Probably a bit slow asking this question since I have been running elec pump for a few years.
    Bit concerned with the current direct hook up to ignition that if something goes amiss I will have fuel pumping out until the battery goes flat or a fireball turns it off.
    Vague memory of some posts advising fuel shut off and a relay that 'reads' the dizzy?

    I'm pretty slow on lectrics so keep it simple please.
     
  2. 1500king

    1500king Well-Known Member

    Messages:
    1,545
    Location:
    Adelaide, SA
    You can buy a "tachometric" relay from an Auto LPG supplier along with a fuel cutoff solenoid. (relay approx $20, solenoid approx $60.)

    You can bolt the solenoid to the fuel pump using a double male 1/8NPT pipe fitting(using Loctite gas pipe sealer on threads to avoid leaks) and a 3/16 barbed fitting(with male 1/8NPT end to bolt into pump and solenoid at each end)... Once you have that set up, wire the relay with a fused ignition wire (10A is good) to "+" input, then output to both solenoid and pump. Bolt the relay to a ground point(the mounting tab is the ground), then the tach signal to "-" on the coil(follow wiring instructions supplied with relay)...

    When done, as soon as you turn the ignition on, the relay will "prime" for 3 seconds(turning on both the pump and shut off solenoid), then stop. As soon as you start cranking, then the relay will turn back on when it has a signal from the coil and off you go. When the engine stops running, the relay shuts the pump down and shuts off the cutoff solenoid.

    Nice and simple, mount the pump unit on the rear seat firewall above the trans nose cone and plumb the tank to the cutoff solenoid end, fuel pump end to carbs... Keeping all the working bits close to the tank for effective shut-off and out of the engine bay.

    This setup performs ALL of the functions of the original fuel pump.
     
    onetrackwonder and syncro like this.
  3. Mordred

    Mordred Super Moderator Staff Member

    Messages:
    2,830
    Location:
    Penna, Hobart
    If you can throw up some pics, I reckon this should be a sticky. There are lots of people that would benefit from this info.

    Adrian
     
  4. Burnstar

    Burnstar Member

    Messages:
    94
    Location:
    Artarmon
    Fitted a Tachometric relay to the Kombi on the weekend, no more electric pump being constantly on whilst the ignition is on and engine off.

    Relay was approx $50 from JustKampers
     
    Kai likes this.
  5. Alpal

    Alpal Moderator Staff Member

    Messages:
    8,508
    Location:
    Melbourne Bend of Islands
  6. Rocky

    Rocky Well-Known Member

    As 1500king put up, this is the best solution.
    An alternative (without the cut off solenoid) is possible using a couple of standard 12V relays - I will dig up the wiring info, but basically it works as follows. One relay is to ensure that the pump in off if the starter motor is off, one ensures that the pump is off if the alternator is off. They are wired so that if neither one of the starter motor and alternator are connected, then the fuel pump cannot be connected.
    Obviously a positive fuel cut off solenoid is a great addition to either this system or to the tachometric relay system. This is just a neat way to utilise existing and cost effective relays.
     
  7. grumble

    grumble Well-Known Member

    Messages:
    1,045
    Location:
    Taree
    The Bosch relay with a normally closed contact is much easier than the double relay setup as there is only one relay used.
     
    Rocky likes this.
  8. syncro

    syncro Well-Known Member

    Messages:
    9,382
    Location:
    Southern Highlands
    Do you have any details of that as I cannot imagine how it would be connected?
     
  9. autron

    autron Member

    Messages:
    76
    Location:
    victoria
  10. autron

    autron Member

    Messages:
    76
    Location:
    victoria
    when ign is on and motor not running power to pump stopped at open contacts on standard relay as changeover relay is on due to alt warning light wire being a negative when alt at rest not spinning. when cranking power to pump is achieved as standard relay pulls in. power to pump when motor has started is achieved by changeover relay dropping out as alt warning light wire becomes a positive . i hope i have explained my self ok
     
  11. syncro

    syncro Well-Known Member

    Messages:
    9,382
    Location:
    Southern Highlands
    Easier to use 2 NO relays but that would work.
     
  12. autron

    autron Member

    Messages:
    76
    Location:
    victoria
    can you please explain thanks
     
  13. syncro

    syncro Well-Known Member

    Messages:
    9,382
    Location:
    Southern Highlands
    Relay on left term 87 to 15.
    Second relay Alternator D+ to 85. - to 86. 15 to 30, fuel pump to 87.

    When 50 is energised the left relay supplies to the pump.
    When the alternator is charging D+ operates the second relay which supplies the pump. (Similar to the Kombi heater relay)
     
  14. Rocky

    Rocky Well-Known Member

    I'm pretty sure this is how I did it. I am not with the kombi now so cannot confirm, but this would allow power to the pump while cranking, or power to the pump while the alternator is producing power. The only drawback I guess is that if you are in gear and rolling and the alternator is still giving twelve volts then fuel would still pump... Other than that scenario, if you are not cranking and the engine is not being driven, then the fuel pump will not have power. This utilises two standard 12v relays. 20150728_154629.jpg
     
  15. Kai

    Kai Well-Known Member

    Messages:
    4,734
    Location:
    Sydney, NSW
    why use 2 relays when you can just use one. its it really simple.
     
    syncro likes this.
  16. Rocky

    Rocky Well-Known Member

    When I set mine u; I had a bag full of standard relays and found it quite simple with 2...
     
  17. saabman

    saabman Well-Known Member

    Messages:
    4,800
    Location:
    Goulburn
    Or connect the pos of relay to ignition and the relay gnd to the oil pressure switch.

    Once the starter starts turning the engine over it will raise the oil pressure and the pump will start.

    If the oil pressure drops either by no oil or stopped engine the pump will stop.
     
  18. Alpal

    Alpal Moderator Staff Member

    Messages:
    8,508
    Location:
    Melbourne Bend of Islands
    The Tachometric Relay connected to the coil runs the pump for a few seconds before it cuts out. Primes the fuel system ready to run when you crank it over. Seems a good idea. Just fitted and it works well.
     
    Burnstar likes this.
  19. Burnstar

    Burnstar Member

    Messages:
    94
    Location:
    Artarmon
    My only issue with this is if the bus breaks down this will make troubleshooting more complicated.
     
  20. Kai

    Kai Well-Known Member

    Messages:
    4,734
    Location:
    Sydney, NSW
    you'd need something to prime the pump.
     

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