Fuel Pump gets no power

[zewald]

Hey guys, i have a 75 280z, and it's taken me about 2 months of spinning my wheels to finally get on here and ask about this problem. I've looked at everything i can think of in the car. my fuel pump will not pump gas into the engine, it's not getting any power. i've checked the connections, and gone through as much of the harness as i can get to at the moment. and i haven't been able to find any problems, i replaced the pump to no avail. (i tested the old one and it definitely was faulty anyway) but i was wondering what else i should check to find the problem. this car has been my dream car for a long time, and i really want to get the thing up and running. any help would be appreciated.

[BrianL1987]

I'm no expert on 280's but, have you check with test light to see if it is 12v or, ground that is faulty? If you've already checked the basic: fuse box & (in-line fuse?) I would just run new wire to solid power source. FYI- Mine was wired to coil by PO & figured out that it was robbing power from coil at higher rpms.

[zewald]

i don't have a test light. where could i find one? and the problem is that even when cranking the engine, the fuel pump gets no power. i've checked all the grounds and gotten rid of all the corrosion i could find, so i just don't know what to do next.

[Zed Head]

If you don't have a test light or a voltmeter, then how do you know the pump is not getting power? When you say "no power" do you mean "no noise" from the pump? Or have you checked with a voltmeter?

Most auto parts or hardware stores will have a test light for sale.

Do you get spark? Will the engine start on starting fluid? If no spark, check your EFI harness fusible links.

[zewald]

i checked with a volt meter. and the engine does spark, it's run for as long as 30 seconds on starter fluid. where is the fusible link for the fuel pump? i've checked the fuse box and replaced blown fuses, tested the fuel relay, the control unit, and will check the AFM tomorrow. thanks for replying by the way. both Zed Head and BrianL1987

[cozye]

trace back through with a voltmeter using the FSM wiring schematic (if you don't have this it's available for download). There are two relays, fuel control relay and a fuel pump relay (at least on the 77-78 there are two). The AFM switch mentioned is a an easy test as well. Go back until you hit a 12v signal and you will know where the problem is.

[zewald]

that's great man, thanks. hope it works. with gas prices the way they are, i need to start driving the thing so i get better gas mileage than in my truck, haha.

Edited March 8, 2011 by zewald

[Zed Head]

I'm not sure what you know but the fuel pump only runs when the starter is engaged and when the AFM pump contact switch is made, for 1975. It doesn't run when the key is at On, unless air is flowing through the AFM.

So one way to check the power lines to your pump is to disconnect the small wire from the starter and turn the key to Start. The engine won't crank but the fuel pump wire will get power if it is connected and working correctly. If you do that and find that the pump runs, then you can move on to why the injectors aren't opening.

Maybe you've already done this. Some people expect the pump to run when they turn the key to On.

Another way to check is to take the air intake hose off of the AFM or take the side cover off and rotate the vane while the key is at On. This will get the relay to feed power to the line also.

Fuel pump power runs through the fuel injection relay. I don't see a fuse on the diagrams but there might be one.

[cozye]

Good advice Zed.

Zewald, if you are expecting good gas mileage, don't get your hopes up too much. 19-20 mpg seems to be about the average for an EFI 280z.

[Zed Head]

Thanks cozye, I was writing while you were posting so didn't see yours.

And 19-20 mpg is about exactly what I get in my 76. Seems to go up a little in warm weather and down in the cold.

By the way, the 75 and 76 (maybe 77) have a combined fuel pump and fuel injection relay. Both relays in one long housing, up above the hood release handle in the cabin. The fuel pump relay takes its signal from the AFM to turn the pump power on. They are expensive.

[olzed]

Speaking of gas prices, we are currently paying $2.16 per litre for the cheapest stuff in NZ, and it's expected to go higher. Thats over $8 a gallon at a guess. The sooner that the problems are sorted in the Arab countries the better.

Sorry to hijack.

Brian.

[FastWoman]

I feel your pain, Brian! I'm starting to think, "Geesh, what have I gotten myself into?" I wonder whether our machines would be capable of 30mpg with more modern EFI systems -- like the Megasquirt.

Zewald, do everything Zed said! Great advice! Instead of listening for the pump to run, you might watch for fuel pressure -- e.g. with a gauge on the fuel line. Some pumps are only barely audible. (I can barely hear mine. It's a soft, low, rumbling.) If you have a fairly new fuel line somewhere (e.g. between the fuel filter and the fuel rail, you can just squeeze it with your fingers and feel it get firm when it becomes pressurized.

Beyond that, just trace out all your wiring with a schematic diagram. Don't forget to check each and every connector for signs of charring. The pump draws a lot of current, and the contact in my big wire harness connectors had gone bad, charring the contacts and melting part of one of the connectors.

Edited March 8, 2011 by FastWoman