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Thread: Wiring Path for Electric Fuel Pump

  1. #1
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    Default Wiring Path for Electric Fuel Pump

    Working to get a car back on the road after a 20 year nap. Tank has been cleaned and reinstalled. Working to replace the electric fuel pump. However, power dose not seem to be making it back to the fuel pump.

    A kill switch was placed under the dash and that seems to work, power goes in and comes out of the switch and to the harness connector in the console under the radio, but no power is making it to the connector at the fuel pump.

    There are two wires at the pump with bullet connectors, one is ground (black wire) and I has been tested for continuity, the other will not read. I figure that there is a break some where between the console and the back of the car.

    How dose this harness route to the back of the car? I see it go up in the RH quarter panel, but what do I need to remove to trace these wires?

    Any help greatly appreciated.

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    Registered User madkaw's Avatar
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    First post? Welcome!
    Fill out your signature so we know what year car you are referring to.
    The green wire or power on the early models weaves under the dash passenger side and then follows the harness along the passenger side. Should be green and black wires at the pump.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Registered User rossiz's Avatar
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    with the key on you can pull the plug off the oil pressure sender (down low on the block, passenger side) and the pump should run - at least it should get power...
    as a safety feature the fuel pump is wired to shut off if there's no oil pressure, in case of an accident where the engine is shut off and a line is ruptured.

    there's also a fuel pump relay to check - some of the other electrical gurus will have more specifics on these, but you should be able to hear the pump running which should help you test for the bad connection.

    while you're at it, might want to replace the fuel filter up front - if the tank was dirty/rusty there's a good chance that filter is toast.
    '78 280z - Daily driver/work in progress...

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    Ah. Oil pressure switchn got it. I hear a click under the dash when key is set to run. Will check at oil pressure switch and then check for power again. Yes will be changing fuel filter as well.

    Had engine running from gas can and electric pump up front just for temp to see if engine was good. So far, everything is checking out.

    New clutch master and slave,and hose, new brake master everything bled. Just need to take around block to see how things feel, then wheea will come off to do full brakes

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    Registered User Jarvo2's Avatar
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    Here's a quick link to my write up as well as a diagram that I drew when I added an electric pump to my '72 240z...

    Dave's 1972 Datsun 240z: Electric Fuel Pump Installation

    Click image for larger version. 

Name:	FuelPumpSchematic_v2.JPG 
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    Dave
    Windy City Z Club (Chicago)
    1972 240z, restoration in progress
    http://jarvas240z.blogspot.com

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    Rust Free'ish zKars's Avatar
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    Whoa boys. We don't even know what year of Z we are dealing with and we are telling him to go check a fuel pump relay. There are no fuel pump relay interactions until at least the first FI cars. And only some 72-73's had an electric pump in the back, and none of that wiring involved a relay, let alone a oil pressure switch!

    Blackbirdpilot please update at least your first post with your Z details first, THEN we'll put you on the right path.
    Last edited by zKars; 09-03-2014 at 08:05 AM.
    -----------------------------------------
    Jim
    73 240Z HLS30 149331
    69 510 PL510 77603

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    Registered User madkaw's Avatar
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    I guess Blackbird didn't read my post
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Sorry for the delay on the sig update. Was having lots of issues logging. But here are the details none the less. It is a 1973 with 4 speed and AC. Has domed Carbs, not the flat tops.
    1973 240Z. 4speed w/AC. Dome top carbs

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    This might help..

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    Ok, I've found the relays.... now dose someone have a wiring diagram that shows what pin dose what?
    1973 240Z. 4speed w/AC. Dome top carbs

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    No more body roll! SteveJ's Avatar
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    Tell me what wires go to what pins, and I can probably tell you what the pins are.
    73 240Z
    74 260Z

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    Looking fot the pin out that feeds power to the fuel pump from the realy so I can see if power is going in and comming out if realt to the fuel pump.
    Am I looking for a green wire going in and a green going out or what pin on the connector feeds out to the pump.
    1973 240Z. 4speed w/AC. Dome top carbs

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    Ok. Im starting to understand how this works. Found the two relays. I see how they are connected. Now, it seems that im not getting power to relay A.

    So im trying to understand the chain of events that trigger the fuel pump.
    1973 240Z. 4speed w/AC. Dome top carbs

  14. #14
    No more body roll! SteveJ's Avatar
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    Relay A is energized by a wire between the alternator and regulator. When the engine is running, the alternator is turning, and the coil is powered.
    When the contacts for Relay A closed, Relay B's coil is energized.

    If someone removed the harness that energized Relay A, Relay B will never get power on the coil. This might be the case if someone converted the alternator to an internally regulated unit and removed the voltage regulator. After that conversion, Relay A will always be energized unless the harness for Relay A is removed. That will run down the battery.
    Been there.
    Done that.
    Got the t-shirt.
    73 240Z
    74 260Z

    Blue's collection of tech tips - A great place to look for answers
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    I don't think I would look that good in that T-shirt. Does it come in 2XL?
    73 240Z
    74 260Z

    Blue's collection of tech tips - A great place to look for answers
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    Haha!!

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    So then, how dose the pump engerize from a cold start? Will A engerize while cranking, untill the Alt starts charging?
    If the Alt fails to charge, will the pump cut out?
    1973 240Z. 4speed w/AC. Dome top carbs

  19. #19
    No more body roll! SteveJ's Avatar
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    Quote Originally Posted by BlackBirdPilot View Post
    So then, how dose the pump engerize from a cold start?
    The electrical pump doesn't pump at the start.

    Quote Originally Posted by BlackBirdPilot View Post
    Will A engerize while cranking, untill the Alt starts charging?
    No.

    Quote Originally Posted by BlackBirdPilot View Post
    If the Alt fails to charge, will the pump cut out?
    Yes.

    Remember, the mechanical pump is the primary pump. The electrical pump was integrated in to deal with issues associated with the flat top carburetors.
    73 240Z
    74 260Z

    Blue's collection of tech tips - A great place to look for answers
    XenonS30 -The cheap source for FSMs
    Georgia Z Club
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