Hey all,

Couldn't find much info on this after some searches....

I am replacing my stock L24 with a reman 280 ZX F54/P79 motor, and am trying to figure out fuel pump issues. Here's what I know:

1) The P79 head has the mech fuel pump hole blocked off (or rather, not cut out of the head casting) because of the nature of high pressure FI setups, and that all 280ZXs came with electric fuel pumps.

2) Low volume/pressure fuel pumps (3-4psi) are available for 240Zs.

3) The wiring for early electrical pumps (1973-74 carbed 140/260Z)seems to be relayed such that the pump is on to prime the motor, then essentially off when the motor is running (most of the work done by the mech fuel pump)...

4) My 5/72 wiring harness does not have the same relay setup as the 1973s. The car has the wires for the fuel pump near the tank, but I don't know where those wires go, because...

5) I don't have a reliable 1972 240Z wiring diagram:dead:

So...what I want is an electric fuel pump that is on when the key is on the "on" position or the "start" position, and off when the key is "off." Does anyone know the way the early harnesses are wired for fuel pumps? Is this possible? Can I have the P79 fuel pump hole cut out and install a mech fuel pump (is that worth it?)? Any other suggestions?

Thanks for your time,

Steve

So...what I want is an electric fuel pump that is on when the key is on the "on" position or the "start" position, and off when the key is "off." Does anyone know the way the early harnesses are wired for fuel pumps? Is this possible? Can I have the P79 fuel pump hole cut out and install a mech fuel pump (is that worth it?)? Any other suggestions?

Is modifying the P79 head worth it? No.

The reason is that wiring an aftermarket electric pump is simple. The factory wiring can be used if you are planning to mount your pump in the back near the tank. The existing wiring is not connected to anything at either end. The other end is located in the wiring under the dash somewhere.

On the other hand, I mounted an inexpensive 4.5 psi pump on the side of my P79 head, right where the mechanical pump would be. That simplifies all the fuel lines. I have a relay that is triggered from the lead from the ignition switch to the coil, that routes power from the battery to the pump. Very simple.

As a final safety precaution, it is advisable to wire a circuit that cuts power to the pump when the oil pressure drops. This is to prevent fuel spills and fires in event of an accident. I haven't done this yet, but will before I get my car back on the road.

Thanks, Arne...

I have always been told that electric fuel pumps are better at pushing fuel than pulling it, hence the tank-mount location. Any problems with a forward-mount?

I wish I were more electrically-inclined--what kind of relay did you use? Was it connected to the ignition wire at the coil, or closer to the ignition switch? How much splicing of the wiring harness did you do? Any inline fuses placed?

How do you propose to make your safety cut-off switch?

Sorry for the questions. Thanks for your help,

Steve

It is true that the electric pumps push better than they pull. But mine seems to work OK pulling, and it was much easier to wire, route fuel lines and mount up front on the head.

Wiring the relay - any normally open automotive relay will work. Same as you'd use for pair of fog lights. I didn't splice any of the factory wiring. The relay has four terminals - one is the ground, one is the power supply (goes to the positive battery terminal with an inline fuse), one is the hot lead to the pump, and the last is the trigger wire which I ran over to the coil and tapped into the positive lead there. When ever the ignition is switched on, the relay is energized by the trigger and sends battery power to the pump.

There are several ways to wire the safety switch. You could use a second relay, but the most elegant way would be to connect the ground wire from the fuel pump relay to an additional oil pressure sender designed for an idiot light. Might take a touch of experimenting to get it right, but it would be simple and reliable.

snip...The existing wiring is not connected to anything at either end. The other end is located in the wiring under the dash somewhere....snip

Arne:

Too much Italian roast coffee for me tonight, I guess. Just checked my FSM (1973, mind you), and it looks like the fuel pump wires, while taped up at the tank side, are connected to the wiring harness. Solid green wire at the pump connection passes into the body harness, and connects to the dash harness via bullet connectors. From there, the green wire splices in to the Black wire w/ White trace which connects the ignition switch to the fuseblock and its 20A fuse. The second black wire at the fuel pump is a common ground wire which also serves the domelight, among others.... I confirmed on my 1972 that the green wire connects to the dash harness, but am not too terribly interested in opening all the tape to find if it's spliced to the ignition circuit. Circuit tester might be a better option!

Which pump did you use? JC Whitney has a number of them, and this one has been recommended as a direct replacement for the pump at the tank location

http://www.jcwhitney.com/autoparts/Product/tf-Browse/s-10101/Pr-p_Product.CATENTRY_ID:2005664/showCustom-0/p-2005664/N-111+10201+600002064/c-10101

Is yours something more like this one?

http://www.jcwhitney.com/autoparts/Product/tf-Browse/s-10101/Pr-p_Product.CATENTRY_ID:2005671/showCustom-0/p-2005671/N-111+10201+600002064/c-10101

Steve

Here's the pump I plan to use when I swap in my L28.

http://store.summitracing.com/partdetail.asp?autofilter=1&part=HLY%2D12%2D801%2D1&N=400178+115&autoview=sku

The first one you posted actually resembles the stock elec fuel pump in the early car that had them. 1973-?

I was originally planning on replacing the stock pump because I thought mine was going out. It's noisy. Here's the one I was looking at bu the JC Whitney one looks similar and the price is right if you want to go for the stock look.

http://www.drivewire.com/nissanparts/catalog/nissan720fuelpump.html

You can open that hole on the head. I have actually done that. Not on a L motor but on a NAPS Z24 that I put in a late 510 that originally had a Z20 in it. I just drilled a hole an finished it with a die grinder, tapped the holes for the studs and put the fuel pump on. If you do that remember to install the eccentric wheel on the front of the cam gear.

The Facet brand pumps are said to be noisy. The one I bought locally is the one in the link below. I got it from my locally owned parts house for $30. That pump is marketed under numerous brand names, and is available in a 2.5-4.5 psi version, as well as a 4-7 psi version. It is fairly quiet when mounted directly to the body, and totally silent when mounted to the cylinder head as mine is now.

http://mgaguru.com/mgtech/fuel/fp201.htm

I've also heard that the early generation fuel pumps from a Mazda RX-7 are perfect for this conversion. But that's what I've heard, no personal experience.

The RX7 pump is a good option, if you can find one. Several people run the carb'd RX7 pump - beandip for one. But I couldn't find an RX7 pump locally or affordably, so that's why I went with the one I did.

Hi Guys,

Holley has a PDF web page that shows how to wire an oil pressure safety switch. Its on page three I believe.

http://www.holley.com/data/TechService/Technical/Fuel%20Pump%20Tech%20Info.pdf

Chris A.

I used a Summit low pressure cutoff switch as my safety switch when i converted to an electric fuel pump. the model number was SUM-G1438. http://store.summitracing.com/partdetail.asp?part=SUM-G1438

They have a pdf that you can download that has the wiring diagram for the switch and fuel pump. You'll also need a relay for this to work, but the pdf covers that too.