Fuel pump not turning on. - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

kkmecham88 · 06-28-2020, 05:52 PM

I got a wiring specialty harness and plugged it into my car and my fuel pump is no longer priming. I ended up replacing the fuel pump relay and the fuel pump fuse is still good, still nothing. I jumped the relay and got it to turn on so now i need to figure out why the ecu isn't turning on the relay like it should. the previous owner wired in a push to start and switches i'm wondering if it has something to do with that. one of the switches turns everything on basically turns it to accessory mode and then you push the push to start and everything works fine. before i got the new harness that switch also turned on the fuel pump on so i think it has something to do with that switch but i dont know where to start on the dash harness.

samotage · 06-28-2020, 05:57 PM

The FSM, read and become acquainted with the schematics, and in particular read the stuff in a general about how to read the wiring diagrams. After that it?s all just work.

The fuel pump relay wire is black with a yellow stripe, find that on the ecu plug, then trace it through to where it fires the relay. Note I think the pin out for the fuel pump relay from the ecu varies from model to model, but the wire has the same code.

Sent from my iPad using Tapatalk

kkmecham88 · 06-29-2020, 10:21 PM

I?ve looked at the fsm multiple times I know what?s going on now just don?t know how to fix it. Pin 104 is the fuel pump relay wire which activates the fuel pump by using a ground switch. The ecu isn?t trigging the ground which is why it won?t turn on. So if I manually ground pin 104 then the relay clicks and the fuel pump turns on. So why won?t it do it by it?s self.

samotage · 06-29-2020, 10:25 PM

What happens at the ecu? Does the pin there drop to ground when the ignition is set on? Note it will run up a few seconds before cutting out to pressurise before start, so you will have to be watching the multimeter when turning the key.

It could also be a fuse

Sent from my iPhone using Tapatalk

kkmecham88 · 06-29-2020, 10:37 PM

I grounded the wire at the ecu so i don?t think any fuses would be bad. And nothing happens when you turn the key. I know that it turns on before actually starting the car but that?s the problem. I?m not quite sure how the ecu grounds the wire out though.

samotage · 06-30-2020, 01:26 AM

It does, low side switching.

Is the ecu getting its on signal from the eccs relay? This is simple enough to test, look for 12v voltage on the two pins that it connects to when you turn the ignition to on.

Sent from my iPad using Tapatalk

samotage · 06-30-2020, 01:28 AM

Low side switching is from the collector of a transistor inside the box of magic smoke (which should remain contained)

Sent from my iPad using Tapatalk

06-28-2020, 05:52 PM	#1
kkmecham88 Join Date: Jul 2019 Location: utah Age: 23 Posts: 32 Trader Rating: (0) Feedback Score: 0 reviews	Fuel pump not turning on. I got a wiring specialty harness and plugged it into my car and my fuel pump is no longer priming. I ended up replacing the fuel pump relay and the fuel pump fuse is still good, still nothing. I jumped the relay and got it to turn on so now i need to figure out why the ecu isn't turning on the relay like it should. the previous owner wired in a push to start and switches i'm wondering if it has something to do with that. one of the switches turns everything on basically turns it to accessory mode and then you push the push to start and everything works fine. before i got the new harness that switch also turned on the fuel pump on so i think it has something to do with that switch but i dont know where to start on the dash harness.

06-28-2020, 05:57 PM	#2
samotage BANNED Join Date: Oct 2018 Location: Melbourne Posts: 88 Trader Rating: (0) Feedback Score: 0 reviews	The FSM, read and become acquainted with the schematics, and in particular read the stuff in a general about how to read the wiring diagrams. After that it?s all just work. The fuel pump relay wire is black with a yellow stripe, find that on the ecu plug, then trace it through to where it fires the relay. Note I think the pin out for the fuel pump relay from the ecu varies from model to model, but the wire has the same code. Sent from my iPad using Tapatalk

06-29-2020, 10:21 PM	#3
kkmecham88 Join Date: Jul 2019 Location: utah Age: 23 Posts: 32 Trader Rating: (0) Feedback Score: 0 reviews	I?ve looked at the fsm multiple times I know what?s going on now just don?t know how to fix it. Pin 104 is the fuel pump relay wire which activates the fuel pump by using a ground switch. The ecu isn?t trigging the ground which is why it won?t turn on. So if I manually ground pin 104 then the relay clicks and the fuel pump turns on. So why won?t it do it by it?s self.

06-29-2020, 10:25 PM	#4
samotage BANNED Join Date: Oct 2018 Location: Melbourne Posts: 88 Trader Rating: (0) Feedback Score: 0 reviews	What happens at the ecu? Does the pin there drop to ground when the ignition is set on? Note it will run up a few seconds before cutting out to pressurise before start, so you will have to be watching the multimeter when turning the key. It could also be a fuse Sent from my iPhone using Tapatalk

06-29-2020, 10:37 PM	#5
kkmecham88 Join Date: Jul 2019 Location: utah Age: 23 Posts: 32 Trader Rating: (0) Feedback Score: 0 reviews	I grounded the wire at the ecu so i don?t think any fuses would be bad. And nothing happens when you turn the key. I know that it turns on before actually starting the car but that?s the problem. I?m not quite sure how the ecu grounds the wire out though.

06-30-2020, 01:26 AM	#6
samotage BANNED Join Date: Oct 2018 Location: Melbourne Posts: 88 Trader Rating: (0) Feedback Score: 0 reviews	It does, low side switching. Is the ecu getting its on signal from the eccs relay? This is simple enough to test, look for 12v voltage on the two pins that it connects to when you turn the ignition to on. Sent from my iPad using Tapatalk

06-30-2020, 01:28 AM	#7
samotage BANNED Join Date: Oct 2018 Location: Melbourne Posts: 88 Trader Rating: (0) Feedback Score: 0 reviews	Low side switching is from the collector of a transistor inside the box of magic smoke (which should remain contained) Sent from my iPad using Tapatalk