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Discussion Starter · #23 · (Edited)
I’ve probably been running around the problem this whole time, but I’m still not sure what it is. Bare with me because I’m not good when it comes to electrical problems, and understanding all of this has had a huge learning curve. I disconnected the fuel pump from the positive cable under the car and left the negative attached. With a set of jumper cables running from the positive wire of the pump to the battery the pump runs perfect, so I can assume the pump is fine? I Then reattached the positive fuel pump wire and connection under the car and placed the probes of my multimeter on the corresponding negative and positive connections of the fuel pump, while turning the key to start, the multimeter gave me a reading of -.30volts. (I’m very new to multimeters so forgive me, to calibrate myself I tested my battery at 12.5 Volts that way I’d know I’m reading it correctly) using the same setting I used to test my battery is what I used on the fuel pump connections and while they were both attached under the car, like I said the multimeter said -.30 So what am I missing?

One odd thing I need to mention, the connectors under the car will only give me a reading without the fuel pump wires connected. If I connect the fuel pump wires and turn the key to start the multimeter will read zero. Without the fuel pump wires the connectors will read -.30. I’ve done this over and over with same results.
 

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Mr.Harrold:

O.K., now I'm getting confused...

We know the pump runs, so the first question is, is it getting voltage on "start".

Disconnect the green/blue wire from the + pole of the pump. Positive probe of the VOM on the green wire, the neg. to the chassis.

With 10ga. white wire off the starter solenoid, turn key to "start", measure the voltage (on "20 volt" scale on the meter) from the green/blue wire.

If you get voltage, there's a problem with the ground.

If reading is minimal or 0, you'll have to look to the relay. If you haven't already, get the wiring diag. @ <https://www.classiczcars.com/files/file/10-1977-280z-wiring-diagram-in-color/>

You will find that the EFI relay diagram (follow the grn/blu wire from the fuel pump) shows two "clicking" relays. You will see that contact 74 is the output to the fuel pump and that contact 73 is the input. You'll have to check for voltage (+ on 73, - on 74) between them with ign. at "start".

If no voltage, check the activation circuit (72 to 70) with key on "start".

Hopefully, you'll get the drift of things once you have the diagram for reference.


To all: if I've erred (wouldn't be the first time), please offer correction.
 

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Discussion Starter · #25 ·
Okay the good news is, I finally have battery voltage running all the way to the fuel pump. With my mutimeter prods on the fuel pump connectors, I can read 11.5v or somewhere around there. Here’s the odd part, it’s still not kicking on the fuel pump. If I straight wire the same fuel pump connectors to the same battery the fuel pump will turn on. But it won’t turn on using the leads under the car, even though my multimeter shows 11.5v. So either way through under the car or via directly from a spare battery the pump is getting 11.5v, but it will only kick on for the spare battery. Am I looking at a busted pump?
 

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Okay the good news is, I finally have battery voltage running all the way to the fuel pump. With my mutimeter prods on the fuel pump connectors, I can read 11.5v or somewhere around there. Here’s the odd part, it’s still not kicking on the fuel pump. If I straight wire the same fuel pump connectors to the same battery the fuel pump will turn on. But it won’t turn on using the leads under the car, even though my multimeter shows 11.5v. So either way through under the car or via directly from a spare battery the pump is getting 11.5v, but it will only kick on for the spare battery. Am I looking at a busted pump?
Well, if the pump turns on when you wire it to the battery its not the pump. If you are getting power to the positive lead that's good, but the circuit isn't completing which is why the pump isn't turning on.

All that to say - the negative wire probably isn't grounded. Touch the wire to the car body metal and try to start the car - it should work. If it does, follow the negative wire and see where it ends - it's probably not connected somewhere.
 

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Discussion Starter · #27 ·
Well when I touch the negative to the metal body unfortunately the pump doesn’t kick on. But the fuel pump relay beside the driver door clicks every time I touch the negative wire to the connector.
 

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Well when I touch the negative to the metal body unfortunately the pump doesn’t kick on. But the fuel pump relay beside the driver door clicks every time I touch the negative wire to the connector.
Are you just touching the pump ground wire to other metal or are you using a separate piece of wire from the pump ground to a good ground on the body?
 

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Discussion Starter · #29 ·
I used a separate wire attached to the pumps negative wire. Every time I touched the separate wire to clean metal, it would just click the relay.
 

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If I may interject, I suspect that at this point, the issue may be one of communication.

In an effort to promote clarity, I suggest that we run through this using a common methodology.

A "by the numbers" approach might look like this:

- Unplug the 10ga. wire at the back of the starter solenoid.

- Connect both fuel pump wires to their respective terminals on the pump (we are assuming that the bullets behind the seat are also correctly connected); Grn/Blu (actually, I'm not sure of the wire color here; it's Grn/Blu into the bullet connectors behind the seat) to the +, black to the -. Leave these wires connected throughout this procedure. Note: you must be certain that you have the polarity correct and the connections are firm.

- Get/build/buy a two-wire set of clip leads (3 or 5 ft. long) with clearly marked ends (red and blk are preferred) to assure correct polarity.

- Clip the red of one end of the clip lead to the pos.(+) pole of the fuel pump, Clip the black of the same end of the clip lead to the neg.(-) pole of the pump. Clip the opposite ends, pos. and neg, to, respectively, the pos. and neg. probes of the VOM, which is set to register Volts. Keep them separated and not grounded.

- Turn the key to "Start" (not "On") and read the voltage. It should be around 12 volts, and the pump should run.

- If the VOM shows no voltage, the problem is in the relay, or one of its connections. Put your VOM on relay plug pin no. 74, turn key to "Start" and check voltage. If no voltage, probe relay plug pin no.48 (this feeds to 74) and turn key to "Start". If there is voltage, the problem is in the relay. If no voltage, the problem is the wire from, or the Air Regulator itself.

- If the VOM shows voltage, but the pump does not run, clip the neg. clip lead to both the neg. VOM probe and to clean metal on the tub or suspension. Again, turn the key to "Start"; the VOM should show 12v. and the pump should run.

- If the pump runs, your problem is in the grnd. (Blk) wire headed to a common chassis ground.

- If you show voltage and the pump still does not run, there are some serious gremlins at work there.

I hope this helps.
 

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Discussion Starter · #31 · (Edited)
In this picture, the negative to the pump is connected to the car. The POS lead to the pump is disconnected from the car. My Negative VOM probe is on the negative connection. And my POS probe is touching the POS lead coming from the car. The VOM is reading 8.81, which I know is low but my battery was dying. But in other instances it said 10.5 etc etc. and oddly enough, the key was only in the “on” position not “start”, even weirder, if I touched the positive pump lead to the car lead, the pump would not run. With the negative still connected a straight wire from my battery reading the same volt. would run the pump if touched to the pump lead.

I even took a video showing me moving my VOM probe from the car lead to a straight cable from my battery and how they were both reading the same VOLT, but when I touched my pump lead to both of them, only the battery cable would run the pump
 

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Mr.255:

I take it you haven't consulted a wiring diagram yet. I suggest that it would be of no small help.

I would note this: you may have voltage at the pump, but without sufficient amperage, it won't run. I'm not sure how many amps the pump draws, but you could check off the NEG pole when the battery is directly connected. Then you could measure the available amps from the relay.

The pump (and the air regulator) is fed through the relay, with power from one of the fusible links. If you don't have sufficient amps, you need to investigate upstream.

Keep at it.
 

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pdx280 and zmanofwashington have previously referred to the relays that feed the pump, as has ensys right above this post. Download the service manual at "nicoclub.com/FSM/280Z/" and study the wiring near the battery on the diagram. Also look at the text of testing components that appears right before the first diagram.
 

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Discussion Starter · #34 · (Edited)
Thanks you guys. I’ll get out and retest that relay. I know the relay passed the continuity tests. But I’ll have to retest plug pins and 74 and 48, thanks for linking the nico fsm, I previously didn’t know which plug pins those were until I saw them in the nico fsm.
 

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Discussion Starter · #35 ·
With the POS probe on relay plug pin 48 and the key turned to start my VOM read -.50. And would drop back to 0.0 when the key was off. Of course if I switched the probes and put the NEG probe on 48 it was a positive .50. Relay pin 88d was getting the same results. Relay plug pin 74 wasn’t reading anything. Some of the other plug pins in that cluster were reading battery voltage however.
 

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Mr.255:

With the hope that doing so will simplify things, I suggest going here (<https://www.classiczcars.com/files/category/1-wiring-diagrams/>) to load the appropriate wiring diagram in an easy-to-read format.

On the 280 diagram, you will find a detailed schematic of the Fuel Injection Relay and all its connections, that will provide clarity, with one caveat: the pin next to 36 is actually "20", not 70. This is important as this is the circuit that controls the relay's two switches.

However, what it does not show is any pin no. 88b.

At any rate, the use of the diagram and the diagnostic procedures in the FSM should yield a successful effort that we all look forward to hearing about.
 

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Discussion Starter · #38 · (Edited)
Found it I think. Haven’t repaired it yet. Power is going through ecu pin 34 but not getting back to the relay. So I connected a spare positive lead to the positive air regulator connector and to the battery, a negative lead to the air regulator and the corresponding connector, and the fuel pump starts running immediately. Without the spare lead the air regulator connector reads 0.0 when key turned to start. So I’m assuming a short in wire 34 somewhere

Added a picture to clear up any confusion. The positive is of course headed to the battery, and the fuel pump runs perfectly.
 

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Sure looks like you found the culprit. Congrats.
Now just finding the break in 34 wire or a connector that is intermediate between ECU and Air Regulator.
 

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Discussion Starter · #40 · (Edited)
How possible is it that the connector itself just isn’t working? I’ve uncovered about 90% of wire 34 and so far everything visually looks okay. Trying to look inside the connector, it looks like it could be mildly corroded, so I sprayed it with parts cleaner, and soaked it in baking soda and water to no avail. Pretty discouraging considering I’m going to have to tape all that harness back up for nothing lol I figured I’d cut the wire at the connector and see if it’s getting power up to the connector and then I’d know. If it wasn’t getting power thought it’d just go ahead and pull it completely through and work in a new wire.
 
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