Fuel pump and Relay problem

[Brae]

I'm having a problem with my 1976 280z. The fuel pump works when I connect a battery to it, and I've checked for continuity on the relay and thats fine aswell, but when I dont have a dedicated 12v, it wont work.

When I try to start the car, it cranks but there is no click from the relay, and the fuel pump doesnt make a sound.

I've tried using the fuel injection bible for this problem (the relay not clicking). When I perform the continuity check for the 2nd step on page 55, I ONLY get continuity when the NEGATIVE is connected to 20 on the control unit and the positive is grounded. After performing this step I tried the one on page 56 but could not get continuity either way. I've checked the fuel pump/wiring/air regulator, and they all seem fine.

Also when I used a battery for the fuel pump while cranking, it still wouldnt start but fuel was going past the filter. Does anyone know how I can fix this, or if me putting a switch to bypass the relay to make a fuel pump switch would solve the problem I'm having? Thanks in advance.

[240260280z]

Did you check the switch inside the AFM that sends current to the pump?

[Brae]

i checked the fuel pump shut off switch and both the input and output have continuity, also i checked the air regulator wires for continuity and the one wire nearest the driver side (i believe #48) does not have continuity. Since that goes to the relay and then the fuel pump, would that be the reason my relay isnt clicking and im not hearing anything from the fuel pump? If that's the case, how do i change/fix that wire.

[240260280z]

[240260280z]

If the problem turns out to be the relay, here is a peek:

[Brae]

i checked the AFM and did all 3 of the steps for resistance, but noticed for 1 (3b) that it was around 185 ohms and then whenever i had a friend press open the flap, it would increase. I thought it was supposed to decrease when you press it in? On the other 2 resistance checks i had 181.5 ohms so the AFM seems fine from what i understand (and the switch is working). I have a few wires that i have no clue where they go (about 3), perhaps they could be another reason but they did not seem to fit anywhere, other then the black one on the afm that is under the top left bolt, but i dont know where i connect the other part of it to. I'll take pics tomorrow

[240260280z]

follow the wiring from battery to pump and measure 12v as you go at all connectors. Don't worry about other efi components at this time: "work the problem".

Just turn key to on and connect afm switch (move flap up) to ensure power to pump path is in a running mode before you start your hunt.

Here is a wiring diagram:http://www.atlanticz.ca/zclub/techtips/wiringdiagrams/76_280z_wiring.pdf

Edited September 3, 2011 by Blue

[FastWoman]

... and remember that there are also a couple of enormous connectors on the main wiring harness, just on the inside of the passenger firewall. They can get a bit crusty, to the point that the large(ish) current demands of the fuel pump can cause arcing and burning of the contact (which lies in the path between the fuel pump relay and the fuel pump). Of course your relay would still click, even if that contact were bad.

[Brae]

So I did every test under the No start category of the FSM, including the voltage checks and what i've found is this.

1(6) water temperature sensor (13-ground) has no continuity

1(8) Air regulator and fuel pump (34-ground) has no continuity

2(2) Power line circuit is (10-ground) is only reading .04 volts

2(3) injector and dropping resistor terminal steps

A(cylinder 4, 14-ground),

B(cylinder 1, 15-ground),

C(cylinder 5, 30-ground),

D(cylinder 6, 31-ground),

E(cylinder 3, 32-ground),

F(cylinder 2, 33-ground) all are reading .04 volts

3(2) Air regulator - It didn't say to do this one, but it was only reading .05 volts at "start"

The line before the relay, after air regulator is the one that is the problem from what i can tell from the checks for the fuel pump not working, what should I do now, follow that wire and change it out? Lost please give tips.

[FastWoman]

Well, my philosophy is that you should fix problems as you find them, even if they don't have anything to do with what you're trying to diagnose (i.e. your fuel pump not operating). It sounds to me like you have a lot of corroded connections. After decades in very hostile conditions underneath the hood, the electrical connectors deteriorate quite a lot. You'll probably find they're severely corroded. You may even find that the plastic connector bodies are very frail and crumbly. You can replace MOST of them with Bosch-type injector connectors, which you can buy from a vendor named f0rest on eBay:

http://cgi.ebay.com/ebaymotors/injector-connector-kit-6pc-datsun-280z-280zx-300zx-/290452375892?pt=Motors_Car_Truck_Parts_Accessories&hash=item43a04f8954

The throttle position sensor connector can be grabbed off of several other models of wrecking yard cars. The AFM connector can just be cleaned up. (It doesn't get as much engine heat). You should simply spend time going through electrical connectors -- cleaning (DeOxit, lemon juice, WD-40), lubricating, and replacing if necessary. Add a bit of silicone dielectric grease when you re-make your connections. After you've examined and serviced every connector you can find, then take your measurements again.

[Zed Head]

If you did these tests with the key at On, it looks like your Fuel Injection harness fusible link is blown, disconnected or has a corroded connection. It is the single green wire, that looks like some sort of extension with a connector on each end, connected to a white wire directly from the battery positive terminal. If it is in its original spot, it may be attached to the side of the relay box with a long plastic peg. OR, your FI and Fuel Pump relay is bad. It is combined for the 1976 model, attached up above the hood release handle. A silver box, about 1 x 1 x 2".

With the key On you should have battery voltage at the dropping resistors, they are fed directly by the EFI/Pump relay, which is on the circuit with the FI fusible link. There are some good diagrams on pages EF-25 and more in the FSM.

EDIT - Blue covered the relay in Posts #3, 4 and 5. That's the one. His diagram shows where the link is also. It's green.

Edited September 6, 2011 by Zed Head

[Brae]

Just bought the connectors, thanks for the link. Zed head, i just put 4 brand new fusible links in just the other week, is there something else is could be? Ill check the fusible link again but I'm pretty sure its good. I'm Leaning towards it being the relay as my friend said he couldnt get his relay to work either on both of his Z's so he just made a switch for the fuel pump. If I cant get the relay to work I'll have to resort to the switch since the added security is nice. This week I'll try to fix all the connectors and if i find something else/fix it then I'll let you know, wish me luck