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1976 280z fuel pump relay and power


SmokeyRoach

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Hello all,

Can I wire the fuel pump on my 76 280z through a seperate switch from the battery to the pump for test purposes to get the engine running? ..heres why....

I only get power to the fuel pump while cranking..i understand this is correct and is due to the airflow sensor and that the engine only turning will produce power to the pump...all good with that. Well mine does not seem to continue to run "the pump that is" and thus no fuel to the engine, Ive given up.

Since I will be doing a full restore on this car in phases and the fuel system will be replaced I'm not going to try to nick pick it apart but wanted to get it started to check through some things, I know it runs.

Thanks for your help,

Bill

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Can I wire the fuel pump on my 76 280z through a seperate switch from the battery to the pump for test purposes to get the engine running? ..heres why....

Bill- no need to go through all the trouble you are describing. for testing purposes (I am assuming you won't be attempting to crank the engine during a dust storm), you can Just remove the boot between the air cleaner and AFM and insert a screwdriver into the AFM to hold the flap open to engage the fuel pump. When you are done troubleshooting, remove the screwdriver and replace the boot. Also, if you are attempting to troubleshoot the fuel pump, just remove the yellow/black wire from the starter solenoid to eliminate cranking the engine over and allowing the fuel pump to run.

Word of advice and caution - 1) Install a filter between the tank and the pump to catch any debris from the tank. 2) Do not let the pump run dry, as the fuel cools the pump while running.

I only get power to the fuel pump while cranking..i understand this is correct and is due to the airflow sensor and that the engine only turning will produce power to the pump...all good with that. Well mine does not seem to continue to run "the pump that is" and thus no fuel to the engine, Ive given up.

You may want to check into acquiring an FSM if you already haven't, and be able to go through the EFI troubleshooting methods.

Since I will be doing a full restore on this car in phases and the fuel system will be replaced I'm not going to try to nick pick it apart but wanted to get it started to check through some things, I know it runs.

Sounds like you have a good game plan. Good luck with it.

Wayne

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I don't know if this applies to your 280 or not but on my 73 240 the fuel pump power feeds through 2 relays in series. One will block power to the fuel pump while the engine is cranking and the other will block power if the engine RPMs are not over 400 ( or so). But in my case there is also a mechanical fuel pump as well....

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  • 3 weeks later...

Thanks for all the help gents! After getting the FSM on CD etc and a full fuel system/control unit test it appears that the ignition switch is intermittant in the On postion thus causing the fuel pump relay to de-latch here and there.

I would have spent days more except I found it by removing the relay from the metal can around the fuel pump relay and watching the coils energize.

I recall back in 89 when I last add a 280z I had the same problem should have know better...

Bill

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Well I was wrong, new ignition switch is not it...my bad logic. All EFI harness checks "referance FSM 76 Z" and funtional tests check out except for the Power Line Circuit. Pin 10 on the ECU should show 12V with the ignition switch in the ON position. I dont see 12V on pin 10 of the harness.

The solution is to referance the circuit in Fig EF-50 of the FSM. This shows the componets in the mix here are Battery, Fusible Link, Ignition Switch, Fuel Pump relay, harness and the Control Unit.

All these items seem to check out even the wiring both Pos and Grounds.

I have gave up so your help is much appreciated. The engine runs when I hold down the secondary fuel pump relay contacts "the one the latches the other after the key is released from the Start postion. So with that said is there another item I'm missing such as the ECU needing to see RPM's etc.

Thanks in advance I know I'm missing probably the most basic thing here but I now need a 3rd eye ball...

Bill

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Well I was wrong, new ignition switch is not it...my bad logic. All EFI harness checks "referance FSM 76 Z" and funtional tests check out except for the Power Line Circuit. Pin 10 on the ECU should show 12V with the ignition switch in the ON position. I dont see 12V on pin 10 of the harness.

Hi Bill -I am assuming the fusible link to the EFI is good as your fuel pump runs in the start condition. Just to be sure, make sure your fusible links are good and not fried. If they are good, then proceed.

Next, with the key "ON' and battery connected, try twisting the main body harness coming out of the firewall on the passenger side back and forth from where the starter feed exits and the fusible links are. My bet is that you have a loose connection in there. Do you hear the ignition relay at all /or sometimes when turning the key over? If the connection is loose, and you make connection by twisting back and forth, you should hear the ignition relay click on and off, and then get your +12V on pin 10. Very common problem in these cars. Unwrap and repair.

You do have the FSM. you may also want to download the scanned wiring diagram of your car at http://atlanticz.ca/zclub/techtips/

Follow the links to 'electrical' to find what you need.

Best of luck,

Wayne

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Yes got the FSM on CD and wiring diags. Fusable links are good, The ignition relay does come on and is good, I bet its something right in front of mine eyes with the + wire between the ON position and Pin 71 (86c) of the fuel pump relay or the ground to pin 72.

I will let you guys know next time I get under the dash...BTW the motor sounds awesome and runs great!! Cant wait to drive a Z again.

Thanks

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Hey Smokey and all,

I don't think I can be of much help on this one but I was wondering if anyone knows the reasoning for the voltage to the fuel pump to be cutoff while the starter is engaged. I'm thinking that you could disconnect the signal wire from the starter to the relay...I believe this relay is normally closed and it would pass relay power through its contacts.

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  • 4 years later...

I realize this thread is several years old but this where i got at by >searching< Im having the the same problem. I had a buddy of mine put his finger on the inlet of the fuel pump and he only felt suction while cranking. I tested all the fusible links inside the passengers compartment and all have continuity. With the key on the on position I held open the afm flapper and the fuel pump ran. I dont want to crank the car since its night but tomorrrow morning i will test some more. With the fuel pump relay/injection relay and the ignition ON is the pump suppose to build pressure for a few secs and then shutoff before starting the car? Is this my problem?

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Your results show that the parts you tested work correctly. The fuel pump runs when cranking. When the engine starts, you let the key go, but the AFM flap is open now from air flow and the fuel pump keeps running. If the engine dies, air flow stops, the AFM flap closes and the fuel pump stops running. So no problems with your fuel supply to the fuel rail, at least from the fuel pump outlet.

Is there another problem?

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Not exactly. Once I let go of the key from the "start" position and stops cranking the starter/engine the fuel pump also shuts off. Therefore the car dies after a few secs. The fuel pump is new and i added a new fuel filter. I had also added a clear fuel filter before the fuel pump but removed it and just stuck the inlet hose into a fresh clean fuel tank. I also have a fuel pressure gauge connected after the fuel filter. It reads about 38psi if i leave the pump running without cranking the engine.

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I had a similar problem where the air flow would not hold the AFM flap open far enough to get it off of the cutoff switch, so the engine would not idle at low RPM. It ran fine, just wouldn't idle.

If the fuel pump keeps running when you hold the AFM flap open as you described, you should be able to keep the engine running by holding the throttle slightly open after it starts (which should open the AFM flap), or turning up the idle speed with the idle screw (same effect). If this works, then you might have a vacuum leak, which is letting too much air past the AFM flap. Find that or the adjust the fuel pump cutoff switch mechanism.

My problem started when I advanced my timing. The engine needed less air to maintain idle speed so the AFM fuel cutoff switch started killing the pump at idle. I ended up bending the switch mechanism so that it would stay closed at lower air flow.

You can see the cutoff switch and how it works underneath the black cover on the side of the AFM.

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