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just1n962

Jury Rigging Fuel Pump

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    Okay so I've been restoring a 75 280z and it's so close to being finished but for some reason my fuel pump won't kick in when the engine is turning over unless I direct connect a wire from the fuel pump to another wire source that is getting current. Is it okay to do this? If so, where can I hook it up so that it's safely getting enough power, isn't stealing too much power from something else and won't burn up any wires or create a huge electrical problem. Oh, also, where would I hook the negative side to?

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    I have no idea but I did find this from http://atlanticz.ca/zclub/techtips/

    The fuel pump control for the 75 - 77 N/A.

    When the engine is not running the flap in the AFM is closed and the fuel pump control switch in the AFM is OPEN. When the key is turned from "OFF" to "RUN" there is no continuity through the fuel pump switch in the AFM and the fuel pump should not run. When the key is turned to "START" the engine turns over AND the fuel pump relay closes which starts the fuel pump. As air is sucked past the flap in the AFM it opens and the FUEL PUMP contacts in the AFM close. When the engine starts the air flow through the AFM keeps the fuel pump running because the switch is closed. If the engine stops / stalls the flap in the AFM closes and the fuel pump control switch in the AFM opens thereby shutting off the fuel pump.
     

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    It would be best to track down the issue, but yes you can do it that way.  I would not use the wire unless you know the exact load rating what it was designed for.

    Since your defeating any safety fuel pump shut off, it would be best to run new wire to the + side of the pump, ground the - to the chassis and install a Ford inertia shut off switch inline of the + side wire. Youtube it and you will see what a simple device it is and where you can get it.

    Again, Ideally it would be best to figure out what is wrong.

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    The voltage for the coil on the fuel pump relay comes from the Black/White wire. The negative goes from the relay to pin 5 on the ECU. You should read the EF section of the FSM. I suggest using the 76 version since it's a better quality scan than the 75. 

    If the relay coil isn't energizing, the fuel pump circuit isn't complete. I suggest that you not bypass it. Get everything working right.

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    Okay this is great stuff. So I should use a voltage meter with one side on the black/white wire from the relay and the other end on pin 5 of the ecu to see if they correlate? Also, I have a 76 fuel pump relay and fuel injection harness. Does that make a difference? It's all the same connections I believe. 

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    How do you know the pump is not getting power?  It doesn't kick-in, it just gets power when the key is turned to Start.  The simple test is to disconnect the starter solenoid wire and turn the key to Start. You can hear the pump because the engine doesn't turn.  The other one is to turn the key to on and open the AFM vane.  This will use two different parts of the same system.

    How far down did you tear things during the restoration?  And is it a restoration or a resto-mod?  Is the EFI/pump relay still there?

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    Actually check voltage to ground off of pin 72 on the relay (It goes to pin 5 on the ECU). While starting, if it is 12VDC, you don't have a ground. If it is 0VDC, check resistance from pin 72 to ground. It should be low, less than 1 Ohm.

    I am not aware of any major changes between the 75 & 76 systems, so you should be good with those parts.

    Additional things to check:

    Ground for the fuel pump - Does the black wire at the fuel pump connector have continuity with the chassis?

    Does the Green/Blue wire at the fuel pump have continuity with the same wire color at the fuel pump relay?

    Measuring to ground, are you getting 12VDC (battery voltage) at the fuel pump relay with the white/red wire, black/yellow wire, and black/white wire?

    Are you sure you have a good ECU?

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    It was a pretty full restoration, rebuilt the motor and all and stripped most everything out. The ECU should be good. I bought it off of a running 76. I haven't seen any kind of ground for the fuel pump, is there supposed to be one? The black wire that goes to the negative just runs back up through the hatch along with the green/blue and to the hookup on the passenger side. 

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    12 minutes ago, just1n962 said:

    I haven't seen any kind of ground for the fuel pump, is there supposed to be one?

    SteveJ is instructing at doctorate level but you're at 101.  No offense.  You're going to have to learn some basic electrical concepts.  Or just do the simple tests, like listening for noise when you turn the key to Start.

    1975 EFI wiring.PNG

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    None taken. I love the cutting, welding and engine rebuilding part of a restoration but I can admit that wiring is not my forte. I had my dad at the back end listening to and feeling the fuel pump for activity when turning the key and there was none until we connected another wire to the positive end of the fuel pump and the other side of that to the starter ignition switch wire. It was pretty weak but was pumping gas. Definitely not something that could be heard from inside the car. There's probably a better place that I could connect it that would give it more power but I'm not sure where that would be. 

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    my 2 cents, fix it with out having to rig something up, one issue at a time. Its not that complicated, just a relay and the ignition switch (at least the start position) like zh said before, disconnect the starter solenoid wire, have some one turn the key to start, begin tracing to see where the problem is.

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    42 minutes ago, just1n962 said:

    None taken. I love the cutting, welding and engine rebuilding part of a restoration but I can admit that wiring is not my forte. I had my dad at the back end listening to and feeling the fuel pump for activity when turning the key and there was none until we connected another wire to the positive end of the fuel pump and the other side of that to the starter ignition switch wire. It was pretty weak but was pumping gas. Definitely not something that could be heard from inside the car. There's probably a better place that I could connect it that would give it more power but I'm not sure where that would be. 

    Projects like this are great opportunities to learn new skills.  Because the knowledge has immediate impact.  You've mentioned "more power" at least a couple of times, but there is not "more power" available.  It's just the 12.6 volts from the battery.  It's basic direct current electrical stuff.  You shouldn't really be looking for a better place to make a connection.  You should make the proper ones work right.

    Giving good descriptions of what you're doing will help a lot also.  "Turning the key" doesn't tell much because there are three positions to turn to - Acc, Run or On, and Start.  We don't know which you turned it to.

    If you start using your meter to measure voltages you'll start to understand sources and grounds better.  Start at the battery by connecting the positive lead to the battery positive terminal then placing the negative lead on various body and engine parts.  You'll see how grounding works.  And the two tests mentioned for testing the relay are very simple and should be done.  Remove the solenoid wire and turn the key to Start with all of the proper wiring connected properly, and open the AFM vane with the key at On.  Both of those should supply power to the pump.  If you start connecting various wires to other circuits just to get power you'll end up creating more problems.

    It might be that you have a problem with the wiring and a weak pump, both.  But you  should be able to separate the two issues.  Click the Fiddling with Z Cars link at the bottom of SteveJ's posts and go to the Electrical category.  He has some basics in there.

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    Some day I should probably make an instructional video for people to use their meters to diagnose Z electrical systems. There are still plenty of opportunities for tech tips.

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    23 minutes ago, SteveJ said:

    Some day I should probably make an instructional video for people to use their meters to diagnose Z electrical systems. There are still plenty of opportunities for tech tips.

    You should Steve!  I just get lost following the wires in the silly schematic!

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    I'm definitely going to be trying out all of these diagnostics and figuring out more about reading the meter. And when I talked about turning the key I meant that I turned it all the way to start. The engine does turn over and it wants to fire but without gas getting to it she obviously won't. We got her to run for a second or two off of starter fluid. 

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    Don't overlook that if the car sat for quite a while before you got it the gas might be bad, the fuel pump might have rusted, there might be water and/or rust in the tank, it might have made it's way in to the fuel rail and injectors, etc...

    There's a lot missing from the story.  If you define where you're starting from you might save yourself a lot of time and trouble,  People often just throw a battery in to a car and suck all of the bad fuel through the fuel system, hoping the engine will fire.  Then they have to fix all of the damage.

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    Yes, I'm sure theres some crud in there.  You should, if you haven't already, put a Fram G3 clear plastic $3 filter between the tank and the pump.  That short hose is low pressure.

    There's a write up from Blue's Tech Tips with good pictures.

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    I pulled the engine and fuel tank and all the lines. The engine is completely rebuilt and brand new, I took apart the tank, cleaned it out, welded it back together and coated the entire inside and all the fuel lines are new. It's definitely not an issue of crud anywhere. Even with the fuel pump I took that all apart and cleaned every inch of it. This was a full on restoration. The only problem is that the car that I chose to restore had a previous owner who decided he'd take a "what the hell" approach to wiring this thing up when there were issues. 

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    Didn't you post these same photos on FB? They look familiar to me.

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    So, you're up around Toccoa, right? That's not too far from me. Besides, didn't you want to see how my car felt with the Chevette springs?

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    Yes, the engine is in and running great. I could make it up your way around the weekend of the 25th if you want to do some diagnostics.

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    There is a chance that I will be working a shift in atlanta on the 25th but I don't have any info on that just yet. Let's go ahead and shoot for that date and I'll keep you posted once I know more. I appreciate you helping me out here. 

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