Phantom Fuel Pump? Most frustrating!

[2many280zzz]

Why would the fuel pump only operate when the key is in the 'start' position cranking it over? As soon as the Z starts, the fuel pump actually turns off. This is a new low pressure pump for carb conversion that works fine. This, verified by connecting to an external 12v power source. It ran great and I was even able to start dialing in the carb. What gives?

[sblake01]

What year is your 280z? If it's the 75, it would be because you no longer have the AFM hence no signal from the fuel pump contacts in the AFM once the car starts. If it's the 78, it should work providing that none of the other wiring has been changed since that signal comes from the alternator, the oil pressure switch, and the fuel pump relay .

[SteveJ]

My guess is that you're getting your power from a circuit that is only active in the start position. To get a better answer I suggest you do this:

1. State the year/model of the car.

2. State the known modifications, especially if they are related to the system giving you problems.

By doing that, wonks like me can look up wiring diagrams that we've downloaded to give a solution or help you diagnose your problem better.

Also here is a link to some wiring diagrams at Blue's website for the Atlantic Z Car Club. See if one works for you. If you hooked up the fuel pump to existing wires, tell us the colors and maybe we can figure out when the wires are hot.

By the way, bookmark that website. It's one of the best tech tip sites out there.

[JimmyZ]

Not knowing the specifics about the pump and it's relay I'd have to say that it's something to do with the supply to the pump/relay. You need to be more specific about where the system is and what it's hooked up to. Also have you hooked up a meter to the pump to see if it's getting voltage?

Is there a relay or is it just a fused direct link to the pump? Is the pump tied into the ignition system via a relay or is it something using the stock harness in back?? If so then it's probably just a simple matter of finding which wire is hot during "run" and hooking up to that.

[sblake01]

I'm assuming that he's talking about the 75. All you really need to do is bridge the two wires together that went to the fuel pump contact points in the AFM.

[2many280zzz]

I was just telling Lynn that you are quite brilliant regarding this type of stuff. You are correct in that I am converting the '75. Fortunately every wire got labeled as I removed everything. I figured this failure was something to do with the stock setup that would have to be 'plugged back in' to something. The bridging makes sense now. Thank you! The '78 is next. Both are great cars with rather nightmareish injection systems. Threw some money at local 'Z experts':cross-eye: when I didn't live in town yet had no time to troubleshoot and fix it myself. They actually made things worse-jokers. Since, I have found the real experts in Tulsa who could actually teach me something. This fascinating info makes the coming morning much easier and a bit more fun.

With great appreciation~

Brannen (and Lynn thanks you too...her Z)