280z fuel pump wiring

[Rij Martin]

I just swapped from the FI system to some SU carbs on my 1978 280z. For the fuel pump I just mounted a new low pressure pump right where the old one went. I have not touched any of the wiring other than just disconnecting it from the old intake so I could replace the manifolds. I read somewhere that the fuel pump is somehow hooked up to the CPU and pulling it will require you to re-wire the fuel pump so it runs. Is this true? I only read it on one post out of the hundreds that gave information about the swap. If it is connected to the CPU and I am required to re-wire it, does anyone have any experience and could tell me how you did?

[JSM]

If I recall the CPU triggers the fuel pump as well as the AFM. You'll likely have to install your own fuel pump relay either using the alternator as the trigger (ive heard yellow wire) or install an oil pressure trigger switch to trigger the relay. There was a write up not long ago. On here if I recall. 

I searched and can't find it. If I find the link I'll post it. 

This wasn't the link but shows the oil pressure switch I was referring to:

It was very similar to this thread:

 

Edited February 13, 2017 by JSM

[Rij Martin]

Could I just unplug all the wires that go into the engine bay and leave the CPU in the car? Also does the CPU only affect the fuel pump or are there other things that I will need to re-wire?

[JSM]

ECU only controls the FI. I might be crossing my ECUs up but I thought  there was a trigger for the Fuel pump relay.  I know the AFM does for sure. 

[JSM]

After reading up on Fords Inertia switch, I will be using it in as a safeguard when installing Fuel injection in my 240z.  Such a simple device.

[Rij Martin]

I just pulled out the ECU from my car and turned the key on, the fuel pump still runs. I am very happy but at the same time a little confused.

[Zed Head]

Apparently there is a flaw in the design of the fuel pump control system for 1978 and maybe beyond.  If the oil pressure switch is disconnected it will trigger the pump control relay when the key is on.  So, odds are, either your oil pressure switch is disconnected or defective.  The switch is combined with the oil pressure sender, by the oil filter.  You might check there first.

[Rij Martin]

What are the consequences of me leaving this disconnected, or not fixing it?

[JSM]

5 hours ago, Zed Head said:

Apparently there is a flaw in the design of the fuel pump control system for 1978 and maybe beyond.  If the oil pressure switch is disconnected it will trigger the pump control relay when the key is on.  So, odds are, either your oil pressure switch is disconnected or defective.  The switch is combined with the oil pressure sender, by the oil filter.  You might check there first.

That is weird. It should work just the opposite. 

5 hours ago, idgemartin said:

What are the consequences of me leaving this disconnected, or not fixing it?

In an accident the fuel pump will continue to run. Lots of people run fuel pumps without safety measures but it is a risk. 

[siteunseen]

Your car runs and drives without the ECU?  Amazing!

[Zed Head]

6 hours ago, JSM said:

That is weird. It should work just the opposite. 

It's described at the bottom of this page from atlanticz.  It has the positive of making it easy to run the fuel pump, using just the ignition key.

http://atlanticz.ca/zclub/techtips/fuelpump/moreinfo.htm

 The Engine Fuel chapter of the 1978 FSM has a full description of how the fuel pump control works, with charts and diagrams.  The ECU didn't get involved with pump control until late in the ZX models.  

[siteunseen]

1 hour ago, Zed Head said:

 The ECU didn't get involved with pump control until late in the ZX models.  

I read that too quick I guess, I thought he was saying the car ran without the ECU.  Sorry