Wiring in Electric Fuel Pump

[Moltar]

I have a 240z with the original L24 engine, and have recently converted over to an Edelbrock 4 barrel. Needless to say the stock mechanical pump can't keep up with the carb, so I bought an electric Carter to replace it.

 

My question is:

Can I steal power from my fuel sending unit without blowing anything up to power my fuel pump, so should I run a wire to the fuse box?

 

Ultimately I'm trying to get ignition power to the pump, and would prefer not to run 12' of cable through the length of my car

 

Or is there another source of power that I am not aware of that would be a better place to go to?

 

Almost forgot, I'm mounting my pump to the rear differential mounting brace.

 

~Thanks

[ktm]

I have a 240z with the original L24 engine, and have recently converted over to an Edelbrock 4 barrel.

 

Then you are doing something wrong. The stock pump can handle the 4-barrel.

 

Can I steal power from my fuel sending unit without blowing anything up to power my fuel pump

No, you'll fry the line.

 

so should I run a wire to the fuse box?

No. You'll fry whatever circuit you put it on.

 

Ultimately I'm trying to get ignition power to the pump, and would prefer not to run 12' of cable through the length of my car

 

So you'll go through the effort to replace the SUs by swapping manifolds, but running 12 ft. of 10 ga wire is too much?

 

Or is there another source of power that I am not aware of that would be a better place to go to?

 

What year 240z? The 1972 and 1973 240zs (I am not sure about the earlier models) have a wire with an inline fuse near the fuse box for an electric pump. They also have mounting points near the rear differential for the fuel pumps as well. However, I would still highly recommend running 10 ga wire to the back to power the fuel pump. Use a relay to power the 10 ga line. The ground wire for the fuel pump can be attached to the chassis. Electric pumps' flow ratings are sensitive to voltage.

 

Almost forgot, I'm mounting my pump to the rear differential mounting brace.

 

The 1972 and 1973 model years already have a mounting point (two capture nuts) for an electric fuel pump.

 

Saying that, the stock mechanical pump is more than capable of fueling your engine. You may simply have jetting issues with the carb, tuning issues, or a faulty pump.

[zedman240]

When I installed the EFI system in my early 70 zed, behind the stereo area was a 2 pin plug with heavy gauge green wire but not connected to anything. That wire was there from the factory, already running to the rear where the fuel gauge and sender live. I just supplied that power from the fusebox to run the EFI pump mounted at the rear. There should be a wire already there; just have to supply power to it.

[Moltar]

Then you are doing something wrong. The stock pump can handle the 4-barrel.

 

 

Thanks for the help.

 

The longer I thought about it, I realized doing it your way (the correct way), was just better. No point in frying anything, as that just makes for more work.

 

It is a '71, so no mounts for an electric fuel pump. Also the carb is a 600 cfm, the stock pump has no problem keeping up with the front two barrels, but when the back two open up, it cannot keep up. I've tried every rod/jet change, but it just doesn't want to keep up with the back two.

 

I don't think the stock pump is bad, as it read an output of 3.1 psi when I pulled it (which matched the FSM spec for it).

[hoov100]

Thanks for the help.

 

The longer I thought about it, I realized doing it your way (the correct way), was just better. No point in frying anything, as that just makes for more work.

 

It is a '71, so no mounts for an electric fuel pump. Also the carb is a 600 cfm, the stock pump has no problem keeping up with the front two barrels, but when the back two open up, it cannot keep up. I've tried every rod/jet change, but it just doesn't want to keep up with the back two.

 

I don't think the stock pump is bad, as it read an output of 3.1 psi when I pulled it (which matched the FSM spec for it).

a 600cfm carb is a little big for an l24, isnt it?

[ktm]

Gotcha. Most folks simply install a 390 cfm or so as a replacement for the SUs. The 600 cfm is a bit much.

 

If you are going to run a line, use a relay to power the pump. Basically, run a 10 ga line from the battery to the relay, a 10 ga from the relay to the pump, a ground for the relay, and an ignition hot source to the relay. You can find out how to wire a relay by doing a quick search here.

[Moltar]

Gotcha. Most folks simply install a 390 cfm or so as a replacement for the SUs. The 600 cfm is a bit much.

 

If you are going to run a line, use a relay to power the pump. Basically, run a 10 ga line from the battery to the relay, a 10 ga from the relay to the pump, a ground for the relay, and an ignition hot source to the relay. You can find out how to wire a relay by doing a quick search here.

 

Outstanding sir, thank you for the help.

[waddiejohn]

My 71 has a blue wire running from the rear if the fuse box to the rear of the car wherethe electric fuel pumps are mounted on the later cars and is switched with the ignition. I tied my electric pump to it and have had no problems for two years now.

[theghosttanker]

Running an electric fuel pump so that it turns on and off with the ignition key is a stupidly dangerous thing! If you look at how electric fuel pumps are controlled by ANY modern car, you will see that they ALL have a system that insures that the power to the pump is cut off in the event of an accident, even if the ignition key is left in the "on" position. Z-cars had a couple different ways of doing this...early cars had a relay controlled directly from the alternator, which prevented the pump from running if the alternator was not moving. Later cars had a relay run off the oil pressure sending unit. Other cars simply have the fuel pump controlled by the ECU. At a bare minimum, you should at least install a relay designed to shut off the fuel supply when it senses the shock of an accident. These are cheap and readily available at NAPA or Rockauto.com.

That being said....having run an l-28 on triple webers that made over 225 HP to the rear wheels, I know that the stock mechanical pump is completely capable of providing all the fuel your car will ever need. The reason you are having tuning problems at WOT with your 600CFM carb is that, with all four barrels wide open, your air velocity through the carb is too low for the carb to properly draw and atomize the fuel. It's too large a carb for the airflow demands of an l-24.Changing the size or type of a carb does not effect the fuel flow requirements to the engine.Fuel flow requirement is directly proportional to the horsepower output, and the stock mechanical pumps are capable of supporting WAY more horsepower than your setup is going to make.If I were you I would quit worrying about the pump and put on a properly sized carb.

[Moltar]

Running an electric fuel pump so that it turns on and off with the ignition key is a stupidly dangerous thing! If you look at how electric fuel pumps are controlled by ANY modern car, you will see that they ALL have a system that insures that the power to the pump is cut off in the event of an accident, even if the ignition key is left in the "on" position. Z-cars had a couple different ways of doing this...early cars had a relay controlled directly from the alternator, which prevented the pump from running if the alternator was not moving. Later cars had a relay run off the oil pressure sending unit. Other cars simply have the fuel pump controlled by the ECU. At a bare minimum, you should at least install a relay designed to shut off the fuel supply when it senses the shock of an accident. These are cheap and readily available at NAPA or Rockauto.com.

That being said....having run an l-28 on triple webers that made over 225 HP to the rear wheels, I know that the stock mechanical pump is completely capable of providing all the fuel your car will ever need. The reason you are having tuning problems at WOT with your 600CFM carb is that, with all four barrels wide open, your air velocity through the carb is too low for the carb to properly draw and atomize the fuel. It's too large a carb for the airflow demands of an l-24.Changing the size or type of a carb does not effect the fuel flow requirements to the engine.Fuel flow requirement is directly proportional to the horsepower output, and the stock mechanical pumps are capable of supporting WAY more horsepower than your setup is going to make.If I were you I would quit worrying about the pump and put on a properly sized carb.

 

Ah, you have summed up exactly what I've been trouble shooting for the past week.

 

The 600 cfm is too big for the little L24.

 

The electric pump is far too noisy, not to mention dangerous now that you bring up the crash safety notion, I failed to think (who ever thinks they will get in a wreck?). Thank you for the insight on that one.

 

I'm planning on switching back to the SU setup, just because it responded a lot better than a 600 edelbrock (duh...).

 

~Thanks again, you confirmed what I've been pondering.

[boostiswhatsfordinner]

Running an electric fuel pump so that it turns on and off with the ignition key is a stupidly dangerous thing! If you look at how electric fuel pumps are controlled by ANY modern car, you will see that they ALL have a system that insures that the power to the pump is cut off in the event of an accident, even if the ignition key is left in the "on" position. Z-cars had a couple different ways of doing this...early cars had a relay controlled directly from the alternator, which prevented the pump from running if the alternator was not moving. Later cars had a relay run off the oil pressure sending unit. Other cars simply have the fuel pump controlled by the ECU. At a bare minimum, you should at least install a relay designed to shut off the fuel supply when it senses the shock of an accident. These are cheap and readily available at NAPA or Rockauto.com.

That being said....having run an l-28 on triple webers that made over 225 HP to the rear wheels, I know that the stock mechanical pump is completely capable of providing all the fuel your car will ever need. The reason you are having tuning problems at WOT with your 600CFM carb is that, with all four barrels wide open, your air velocity through the carb is too low for the carb to properly draw and atomize the fuel. It's too large a carb for the airflow demands of an l-24.Changing the size or type of a carb does not effect the fuel flow requirements to the engine.Fuel flow requirement is directly proportional to the horsepower output, and the stock mechanical pumps are capable of supporting WAY more horsepower than your setup is going to make.If I were you I would quit worrying about the pump and put on a properly sized carb.

 

So im running my mechanical pump alone. But im having problems with it keeping fuel in the line. I bypassed the electric pump and itll run for a little bit but will stop running and when i take the fuel feed line off there is no fuel. I dont know whats up.

[waddiejohn]

The Fox body Mustangs have a really neat part to shut down the fuel pump in event of a crash.

[S30TRBO]

When I installed the EFI system in my early 70 zed, behind the stereo area was a 2 pin plug with heavy gauge green wire but not connected to anything. That wire was there from the factory, already running to the rear where the fuel gauge and sender live. I just supplied that power from the fusebox to run the EFI pump mounted at the rear. There should be a wire already there; just have to supply power to it.

 

 

On my 1/71 it was taped off in the rear on the harness for the sending unit. Nissan did think ahead and planned for us EFI upgraders.....