So they gave us electric fuel pump wires?

[cygnusx1]

My 72 will be getting Webers so I installed an electric fuel pump. It was nice of Datsun to give us pre-installed wires for the pump. They run from the radio area back to the fuel level sender area. A black and a green wire with T-Connector up front, and bullets in the back.

Now that the pump is connected to the bullet connector out back, what should I do with the T connector up front?

I need switched power for the green wire and I suppose I can just ground the black wire. But this is a fuel pump we are talking about. What is the proper way to wire a fuel pump so that it stops pumping if the engine stalls? In the 280Z, Nissan used a switch in the AFM. What do we use in a 240Z?

[beandip]

The way I handled this was to put a pressure switch at the oil sending unit that switches on at 5 psi. and off with the loss of oil presser below 5 psi. All that is needed is to buy a tee at your parts store and a pressure switch with two spade connectors. Cut the power wire going to the pump, green one, and run a wire to the pressure switch , then a wire from the pressure switch back to the other end of the cut green wire. Now when you turn the key to the on or start position, the pump will not run. The engine will start and run with the gas in the float bowls . When the engine starts you will activate the pump. If you crash or the engine stalls and the oil pressure drops the fuel will stop.

This setup saved me from a likely fire .

Total cost involved here is about $8.00. If for some reason you need to by-pass the p-switch. Just take a modern type fuse , pull the two wires from the p-switch and connect them to the fuse. Turn the key to run or start and the pump is active. Like if you run out of gas or something and you want to start the engine.

I may have made it sound complicated , but this is a simple mod. Your oil sender connects to the tee along with the presser switch. I took my sender with me to the parts store so I could be sure of the thread sizes .

Gary

[ChrisZ]

There is also another way of doing this, the 260Z way, on the 260Z the altenator pulls a relay and there is also a 2nd relay, this is connected to the starter, that relay cuts off the power to the pump while cranking, so the pump will work in ON but not in START mode, go xenons30 and download a 260Z FSM.

Chris

[Zs-ondabrain]

The stock connector for behind the dash area is just an inline fuse loop that plugs in there. I think it's a 15 amp fuse? I could be wrong.

Dave

[ChrisZ]

It shouild be a 20A fuse, but ive read about melting wire issues so i wont go any higher than 15A as Dave points out, search, it have been covered before.

Chris

[cygnusx1]

I searched "fuel pump wires". Didn't find out any detail on how to make the pump crash/stall safe on a 240Z. I figured that there was a way through the alternator output, but the oil pressure switch is a neat trick too. I also see listed, at rockauto.com some pump control switches that look like roll-over protection. They may be mercury switches, not sure.

[oldhemi]

To implement a cutoff switch; Tip from Tony D:

I have always used an interrupt switch from Ford Products (Tempo-Topaz have them in the left rear corner of the trunk, Ranger Pickups under the mat on the passenger's floorboard).

I bolt them to the bulkhead where the wires go through the floor on a 280Z for the stock electric fuel pump. If you get hit hard, or roll over this switch will trip. You simply reset it with a push of the big red button on top.

Curiously, it's the same part Pegasus Racing sells for crash/rollover pump interrupt as well! Looks the same at least. But boosting it from the junkyard is cheaper and you can dissect the wiring harness on the trunk mounted location to get at least one meter of heavy gauged wire on all the connections...it's almost enough to go from fusebox tap to fuel pump.

I am not sure what the 280Z has in way of wiring that Tony Refers to.

The 260Z uses engine RPM to cut off the electric pump, so its *NOT* used during start up!

Here is info from Steve Golick on the 260Z set up:

Electric Pump Operation

Here’s what the 1974 260Z service manual, section EF Fuel System, page EF-7 says:

This system controls the operation of the electric fuel pump according to the engine speed. It receives the engine speed information from a voltage generated by the voltage regulator. When the engine is running below 400 rpm, the electric fuel pump cut relay #1 remains OFF and the pump will not be operated. While cranking the engine, the electric fuel pump relay #2 remains OFF and the pump will not be operated.

Under normal engine running conditions, both the electric pump and the mechanical pump are operated.

As part of pre-planning exercise (gleaning info from various members - Steve, Zsonda, TonyD, Beandip, ezzzzz) a general wiring cleanup/upgrade project, I am considering deleting my 260Z electric pump and its associated relays and wiring along with the seatbelt interlock system. Notice, I said "considering". As implemented, the electric pump does nothing on start up. I also run a fuel pressure regulator into my Weber 40DCOE's because the mechanical pump is more than enough for me! YMMV.

Edited March 7, 2010 by oldhemi

[Zs-ondabrain]

On my 260Z project, I plan to run a 10 gauge power wire to the rear of the car and use a standard relay off that power wire, controlled by the regular fuel pump wire. This will severely reduce the current going thru the stock relay wires so I won't have a melt down up front.

I plan on running my 40 DCOE's and a mechanical fuel pump block off plate. trying to keep that 4 PSI is tough on the mechanical. probably go with the carter and fuel pressure cut-off.

Dave

[oldhemi]

Dave - 10 GAUGE!!! How many amps does that fuel pump consume? Or am I missing something that you have unearthed in this snakes nest of excellent '70's engineering? Are you considering using one of the original relays?

I hope you share this because I have a 260Z and would like to go a better way. I understand now that my add on regulator is tough on the pump. I did connect the return line 14 years after I initially installed the Webers because I was concerned with the Houston Heat. Still have both original pumps. Not sure if the electric pump ever worked again after I disconnected the seat belt interlock and then later installing a points dizzy after having many problems with the "ecu". I got unplugged wires all over the place form my temporary fixes - decades ago.................

[cygnusx1]

Thanks. rockauto.com has the fuel pump inertia switch for $23.00. Small price to pay for safety. Unfortunately they also want $25.00 for the connector but I can make that up.

AIRTEX Part # 1S3906

Edited March 7, 2010 by cygnusx1

[Zs-ondabrain]

Dave - 10 GAUGE!!! How many amps does that fuel pump consume? Or am I missing something that you have unearthed in this snakes nest of excellent '70's engineering? Are you considering using one of the original relays?...............

I'm doing 10 gauge for a few reasons actually.

1) The distance from the batteries distribution block, on the firewall, to the very back of the car.

2) The fuel pump will pull 12 to 16 amps, The Brake lights will each have a small relay as well.

3)Anything else I decide to add back there will have a good power supply.

I'll also be running a 4 gauge power wire along side that for the 2 amps that will be located in their new homes in the quarter panels. I might also tap that wire for the new Pioneer AVIC-Z110BT's memory and power wire. And maybe even the Power windows, alarm and shaved door popper's.

But at least the fuel pump, no matter which one I end up with (maybe even the stock unit) will have sufficiant power and NO strain on the stock system, due to the power wire and relays.

Dave

Now back to the subject.....

[Walter Moore]

The Holley electric fuel pump that I put on my Z (from Summit Racing) came with instructions specifying that it needs to be protected with a 7 1/2 amp fuse. I used 14ga wire and thought that was overkill.

10ga wire is fused at 30A in house wiring. On a car it would be expected to carry the full output of the OEM alternator. But hey, it is your car. A little extra copper won't hurt anything.