Fuel pump not getting power on 77 280z - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #1 of 24 (permalink) Old 08-20-2018, 12:56 AM Thread Starter
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Fuel pump not getting power on 77 280z

Hey everyone, I’m sure this question has been asked a million times, I’ve read through many of them and haven’t been able to completely solve my problem. I’m not electrical savvy on automobiles so please bare with me. I parked my Z about 6 months ago running fine, no problems. Now it won’t start. When I turn the key in the on position I do not hear the fuel pump. The car will start however with starting fluid. I’ve ran a pair of jumper cables from my battery directly to my fuel pump wires, and immediately the fuel pump kicks on and the car will start and run perfectly, that is until I unplug the cables from the battery. So I know that my fuel pump works fine, and so obviously the pump is not getting power, correct? There is a set of bullet connectors under the passenger seat and from my understanding they run to the fuel pump, using a tester, I see that they have power to them when cranking the car. I’ve checked my fuses, fusible links, and I’ve pushed the afm flap and did not hear the fuel pump kick on. My oil pressure seems fine. Like I said when I inject starter fluid, the car runs great. I’ve read many times that the fuel pump relays rarely go bad, my car only has 93k original miles so I wouldn’t think the relays would be bad anyway. I just don’t know what could’ve happed in the last 6 months that would cause this sitting in a garage.

Thanks all for the tips, I could really use them
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post #2 of 24 (permalink) Old 08-20-2018, 07:06 PM
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When I turn the key in the on position I do not hear the fuel pump. The car will start however with starting fluid.

Ive pushed the afm flap and did not hear the fuel pump kick on.

Seems like you've managed to work around not quite understanding how the fuel pump gets power. It's described in the Engine Fuel chapter of the FSM if you want to get up to speed.

I had the fuel pump relay contact switch in my 1976 AFM get dirty once. Take the black cover off and check it. The fuel pump will only "kick on" if the key is on when you open the flap.
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post #3 of 24 (permalink) Old 08-20-2018, 11:56 PM Thread Starter
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I should have clarified, but yes I have moved the afm flap with the key in the on position and still nothing happened. You are referring to the black cover of the afm correct? Mine is still factory sealed with the original glue so I’ve been hesitant to remove it
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post #4 of 24 (permalink) Old 08-21-2018, 01:10 PM
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Yes, that black cover. It's just pressed on, no clips or latches. Cut the sealant and pry it off.

BUT. The other way to test it is at the fuel pump relay plug. Which is up under the dash by the hood latch lever. Probably easier to remove the black cover.

You can see the tiny little contacts that supply the circuit to the fuel pump relay. A little metal arm that moves with the AFM flap.
They're small because they don't pass much current. With a multimeter or circuit tester you can probe the base of the two legs of the switch to see if the contacts are making contact. a tiny piece of dust or a small hair can stop them from closing. Move the flap and you'll see how it works.

There are pictures on atlanticz.ca. Do not do any of these adjustments! Just look at the pictures. http://www.atlanticz.ca/zclub/techtips/afm/index.html
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post #5 of 24 (permalink) Old 08-21-2018, 11:24 PM
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You can see the tiny little contacts that supply the circuit to the fuel pump relay. A little metal arm that moves with the AFM flap.
They're small because they don't pass much current. With a multimeter or circuit tester you can probe the base of the two legs of the switch to see if the contacts are making contact. a tiny piece of dust or a small hair can stop them from closing. Move the flap and you'll see how it works.
l
My '76 used to shut off on hard cornering intermittently. Found these tiny little contacts were reading about 15-20 ohms when closed. Should have been reading zero, or close to it. I cleaned the contacts by polishing them with a thin piece of cardboard. That was 15 years ago, have not had an issue since!
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post #6 of 24 (permalink) Old 02-06-2019, 10:16 PM Thread Starter
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Well I’m back after 6 months of discouragement. I tried all of the above suggestions without any luck. I know I have power to the connectors under my passenger seat, I tested the connectors with a tester. I’ve cleaned my afm connectors and oil sensor connectors. I really don’t know where else to check. Thanks!
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post #7 of 24 (permalink) Old 02-07-2019, 02:30 PM
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There is a set of bullet connectors under the passenger seat and from my understanding they run to the fuel pump, using a tester, I see that they have power to them when cranking the car.
If the connector has power there when you crank the engine then everything in front of that is working, at least for Start. Does the engine start then die immediately or does it not even pop?

Here's another test that will tell you something. If the connector by the seat has power when you turn the key to Start then it should have power if you remove the small yellow wire from the starter solenoid and turn the key to Start. That is actually Nissan's official factory test method, described in the Service Manual. Much easier to hear the pump with the starter not engaged.

Try that. If there is power at the connector but the pump does not run then the problem is between that connector and the fuel pump. You've been working on the wrong end of the car.
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post #8 of 24 (permalink) Old 02-07-2019, 03:24 PM Thread Starter
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If the connector has power there when you crank the engine then everything in front of that is working, at least for Start. Does the engine start then die immediately or does it not even pop?

Here's another test that will tell you something. If the connector by the seat has power when you turn the key to Start then it should have power if you remove the small yellow wire from the starter solenoid and turn the key to Start. That is actually Nissan's official factory test method, described in the Service Manual. Much easier to hear the pump with the starter not engaged.

Try that. If there is power at the connector but the pump does not run then the problem is between that connector and the fuel pump. You've been working on the wrong end of the car.

Thank you! I’ll try these suggestions when I get home. Could it possibly be the ignition switch? I had a friend tell me since the pump isn’t priming it could be the ignition switch
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post #9 of 24 (permalink) Old 02-07-2019, 04:45 PM
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Thank you! I’ll try these suggestions when I get home. Could it possibly be the ignition switch? I had a friend tell me since the pump isn’t priming it could be the ignition switch
The pump does not prime. There is no priming. The pump only gets power when the key is at Start OR if the engine is running (which causes the AFM flap to open).

There are many people out there who will give you advice even though they don't know what they're talking about. Your best option is to download the 1977 FSM and read the Engine Fuel chapter. It describes everything in great detail.

https://www.classiczcars.com/files/category/13-280z/
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post #10 of 24 (permalink) Old 02-28-2019, 08:51 PM Thread Starter
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Well I followed the Instructions in the FSM, it had me test the ecu for either “battery” or “continuity” and my ecu passed all the tests. I followed all the instructions until it kept telling me to retest. Now retracing my steps with a multimeter, it seems that I’m not getting power under my passenger seat when the key in is the “on” position. With the car running I get power there, I know because I blew a test light checking. With the key in the on position I checked the fuel pump wires with a multimeter. And it shows the slightest amount of power. Connected to the spare battery however it starts pumping. On a new note, I replaced my oil pressure switch, when I turn the key on the oil pressure jumps sky high way past 90. When I use the spare battery to force the car to run, the pressure corrects itself a bit but slowly falls to zero.
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