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Discussion Starter #1
I have a 78 280z.I have no power to my fuel pump. When I ran a wire to the fuel pump from the positive battery terminal it worked. My question is where does the power to the fuel pump come from? Could I just run a wire from a power source that turns on with the key? Thanks.
 

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The pump relay is on the right side of the engine bay under the sheetmetal cover where the EFI and EFI enable relays are. If you can get a wiring diagram from the service manual, you should be able to trace the signals with a test light with few problems. I'd advise against running the pump off the ingnition switch for two reasons 1) You will burn out the switch quickly, the pump needs to be switched with a relay as it pulls lots of current, and 2) If you are in an accident, you pump will continue to pump fuel out possibly broken fuel lines and a hot engine - can you say firey death? You need the ECU to control the fuel pump, so it cuts off when the engine stalls.
 

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SleeperZ is correct in the location of the relays and why you should not drive the car with a hot wired fuel pump. The first relay on the top row of the relay box is the fuel pump control relay, next is the fuel pump relay and then the efi relay. (dont worry about the bottom row...) On the back of the ignition switch is a black wire with yellow stripe. That wire go to several locations, spade terminal on starter, f.p. control relay, f.p. relay, ect... Remove the plug to the ignition switch and put one probe of your multimeter on the black/yellow stripe wire and the other probe on the plug to the f.p. control relay. Do you have continunity? Attach the plug to the ign switch and insert the probe on the black/yellow stripe wire (stick probe in the back of the plug), keep the other probe on the f.p. control relay black/yellow wire. Turn the key to the start position (oh, dial the meter to test for dc volts...) Do you have voltage? If you do not have voltage or continunity, there are several factory crimps in the wiring harness where the black/yellow wire is split off to various places. The crimps are on the engine side of the harness, between the firewall and the plugs to the relay box on the passenger fender. Untape the harness, find the crimps and solder them. A factory service manual (not the Haynes/Chiltons/Clymer books are not worth a toss, so dont waste your time with them), is the most important too for you Z. The efi info and wiring diagrams are worth their weight in gold. There are several places to get a fsm... Do a search in the archives for FSM or factory service manual. You will find the info.
 

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A couple more cents' worth

On the first FI Z cars ('75-76), there was a fuel-pump cutout switch incorporated into the AFM for the exact reasons outlined above (preventing firey death in a crash). If the motor stopped suddenly, as in a wreck, air flap slapped closed, which shut off fuel pump. Datsun switched to another system starting in '77. This involved the fuel pressure sender and . . . well, I think one other component I can't recall right now. Different system(s) but the same purpose — if the engine stopped like in a wreck, dropping oil pressure would automatically shut off the firey death. . . uh, fuel pump. As above, an FSM will allow you to trace down the prob quickly.

Also, you don't mention if the car just started doing this, or has been doing it since you did some work, or what. If you made any mods, I'd carefully go back and either undo them, or make sure I hadn't accidentally knocked off any wires. Finally, Z cars are very sensitive to having clean electrical contacts, particularly under the hood. A good cleaning/recrimping of ALL of them often works wonders on non-working systems — even ones you didn't know weren't working.
 
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