'74 260Z Fuel Pump Wiring Question

[Aerodynamic]

Hi everyone,

 

I have a question about some stupid wires in my engine bay that hopefully you guys can help me with.

 

Now before I start, I am aware of the many threads talking about fuel pump wiring on Z's but I've found no helpful information whatsoever.

 

I am trying to convert to using only the modern electrical pump in the rear of the car, but I'm confused with the wiring.

 

I have traced the wires connected to the pump all the way to the engine bay and they have continuity to the blue single wire in the photo:

 

 

That's great and all, but where does this wire go?  After poring over wiring diagrams I noticed that possibly the above harness of wires needs to connect to the starter and the alternator as "cutoff relays" however there is nowhere to connect them. My pump currently has no power or way of starting.  Here is a photo of the wiring diagram.

 

 

Any info would be greatly appreciated, as I honestly don't know what to do next and this seems like a frustratingly simple problem.

[datzenmike]

Well you should have a mechanical fuel pump and an auxiliary electrical fuel pump. You should be easily able to start on the mechanical pump.

 

The left relay becomes energized when the alternator has little output or stops turning. ( roughly below 400RPMs)

 

The right relay becomes energized and cuts pump operation when cranking during starting.

 

 

You should have electric pump operation only when running and the alternator charging. Hope this helps.

[datsunaholic]

They don't connect directly to the starter or alternator.  The starter feeds one relay, the alternator feeds the other.

 

The "Alternator" one turns the fuel pump on only when the alternator is working, so that in the event of a crash or other situation where the ignition is on but the engine not running, the fuel pump will turn off.  It's to avoid fire.  The issue of course is, the fuel pump won't turn on when cranking, since the alternator isn't spinning fast enough, so there's a second relay to turn on the pump when the starter is cranking.

 

The relays in question are inside the car, probably in or near the passenger side kick panel.

 

 

 

The wires you're looking at (in the engine bay) are for the air conditioning and the FICD, which is also part of the air conditioning.  They have nothing to do with the fuel pump. 

 

That blue wire went to the FICD's magnet valve.  It had multiple points, but essentially it went from the compressor relay to the FICD and to the compressor clutch.  Why it connects to the fuel pump I don't know, but according to the wiring diagram it shouldn't be connected to it at all.

[datzenmike]

The issue of course is, the fuel pump won't turn on when cranking, since the alternator isn't spinning fast enough, so there's a second relay to turn on the pump when the starter is cranking.[/quote}

Doug this is a 260z carb motor and should have a mechanical pump as a primary source of fuel. I can't find this other relay. Later EFI would have a series of relays to get the pump going for start and run the cut out timer if no alt. for safety. The 720 truck even adds a no oil pressure input so the pump motor will quit with low oil pressure.

[datsunaholic]

I was unfamiliar with the 260Z fuel system, so I at first thought he had a 280Z wiring diagram.  Since the pump should be mechanical.  But when I looked at the wiring diagram for a 1974 260Z it shows the 2 fuel pump relays.  I can't think of any reason to connect alternator-fed and starter fed relays to a fuel pump except as a deadman's switch and an override.

 

 

http://www.atlanticz.ca/zclub/techtips/wiringdiagrams/74_260z_manual_wire.gif

[datzenmike]

No you are totally correct. It's an auxiliary pump for when running but there has to be a way of shutting it off in an accident.

[datsunaholic]

OK, yeah, so I'm confused as to why you said you couldn't find the second relay...  ? 

 

When I first saw the question I was completely clueless on this subject, so I went to the books.  Z-cars aren't my thing. I've had one, it was a POS and the only thing it did reliably was break down every 500 miles like clockwork.  I traded it for a basket case 510 Wagon that I still think I got the better deal out of.  The 510 still runs, and I suspect the Z became rebar or tuna cans at least 5 years ago.

 

Was totally unaware that a 260Z had an electric fuel pump at all, let alone TWO fuel pumps. That's why my post was after yours, BTW.  I was verifying the photo of the portion of the wiring diagram really was a 1974 diagram (it is) and then I was trying to figure out what the disconnected wires he pictured are supposed to go to (the A/C system, as it turns out), based solely on the visible wire colors, shape of plugs, and the corresponding part of the wiring diagram.

[datzenmike]

It's all good. I found the 260 had an electrical pump... didn't know that so I looked deeper too. Two pumps, who would have thought?

[maltese]

Once upon a time, I was told the lift pump was a fix for certain Z cars, that had fuel delivery issues using only the mechanical pump. My source was an old school Nissan tech, so I believed his information to be credible. Can't say for sure, since I haven't found literature to back it up.

 

To the OP... What is the reason for eliminating the mechanical pump, in your Z? I'm curious, because I'm switching to triple Webers, which I thought 'required' more volume from an electric pump, but these are running well with the stock mechanical pump in place.

[Aerodynamic]

Hi guys I apologize for the delayed response.

 

@maltese the reason I want to change to just the electric pump with a regulator is for the consistency of fuel pressure flow.  Through my current system the mechanical pump alone occasionally has times where it cannot keep the fuel pressure fully consistent which is obviously an issue.  I am also redoing my fuel system to get rid of all the metal rails boiling my gas so close to the engine and I figured I might as well switch to the electrical pump only since it's already been properly installed.  I just need to figure out how to power it.

 

@datzenmike @datsunaholic Thanks for the input you two.  I've been told to look for the aforementioned relays in the past yet they don't seem to exist on 260s.  It also doesn't help that '74 was a weird year and I have an engine from a 280 in there lol.  Guess I'll just have to keep digging for some kind of solution.  Or just give up and seek out an auto electrician haha.