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munkey_mike

Fuel Pump Only Gets Voltage When Car is Running

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My fuel pump does not get voltage when cranking. I have to manually run voltage to the pump to prime the fuel lines. Once pressurized (over 30 PSI) the car starts after a few seconds of cranking and then the fuel pump kicks on. I have checked the fuel pump relay and fuel pump control relay with a multimeter and the continuity tests come back normal. I have also unplugged the starter lead wire and turned the ignition to start and do not hear the fuel pump. The voltage to the pump only increases VERY slightly when I do this.

 

I'm going to upload a video here in a bit.

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57 minutes ago, jhm said:

Actually, I believe your pump is functioning correctly.  IIRC, accessories are not powered while the ignition switch is in the "Start" position (i.e. when the starter is cranking).

 

 

EF-16 of the FSM says "When the ignition switch is turned to the START position for cranking operation, the fuel pump is actuated irrespective of the conditions of the alternator and the engine oil pressure switch."

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Sorry, my bad....may have been thinking of earlier year model.

 

How are you "manually running voltage to the pump to prime the lines"?  Have you put in a temporary bypass hot lead to the fuel pump that you can control manually?

 

I'm wondering if it's possible for the fuel pump relays to pass a continuity test but still not function correctly to pass full voltage to the pump while cranking the starter?  

Edited by jhm

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Looking at the 78 wiring diagram (available here), it looks like the fuel pump should be triggered by the same wire as the starter solenoid (the black/yellow one that connects to the ignition switch). Since the starter works, I suspect a break between that wire and the fuel pump control relay, or that relay is not behaving as it should.

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37 minutes ago, jhm said:

Sorry, my bad....may have been thinking of earlier year model.

 

How are you "manually running voltage to the pump to prime the lines"?  Have you put in a temporary bypass hot lead to the fuel pump that you can control manually?

I did not install a bypass, I have a Power Probe device. It hooks up to the car battery and there is a probe that detects positive, negative as well as an on/off supply power switch. I probe the positive terminal of the pump and engage the supply switch. Because the pump is already properly grounded, the pump works manually in this way.

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11 minutes ago, NewZed said:

Is it an automatic?  The circled "A" is the circuit for that.  There's an inhibitor relay.

 

image.thumb.png.327547eccc8acda19596aacd8e9ae205.png

 

Hmmm. Yes mine is an automatic. However I did not see an inhibitor relay next to the others when I tested them if this picture is correct:

https://www.zcar.com/forum/10-70-83-tech-discussion-forum/302977-relay-part-280z.html

 

I do remember seeing an unplugged 4 pin connector in there though. I guess it IS possible the previous owner took it out for some reason... I will try to jump it.

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Zhoob's link will have the wire colors.  If you want to be sure.  I think that the inhibitor switch is at the shift lever or on the transmission.  A neutral switch.  The diagram might show location, or the transmission chapter might show the switch.

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1 hour ago, NewZed said:

Zhoob's link will have the wire colors.  If you want to be sure.  I think that the inhibitor switch is at the shift lever or on the transmission.  A neutral switch.  The diagram might show location, or the transmission chapter might show the switch.

 

Yup it's the neutral safety switch. Unplugged the starter wire, shifted to neutral, cranked to Start and I could hear the fuel pump fire right up and fuel pressure shoot up. Thanks.

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Hello D9inger, 

 

That seems a lot easier than finding working relays, I like that the original feature is still there. Would it be a possibility to share how you added these two modern realys to replace the old one and keep the same function. I recently bought a 260z and my fuel pump is not getting power, even when the car is on.

I am new to the thread. Any input will be greatly appreciated.

Thank you

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Thank you NewZed, I think I'll try to figure out a way to replace the original relay with modern ones unordered to keep that function and have power to the pump once the car is running

Appreciate the info. If anybody has ever done this and has an idea, feel free to send it over.

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