No power to fuel pump, seems to be a common problem around here Options

[warrenoliver]

Car stalled on me this morning. When I tried to restart, the fuel pump would not turn on so no luck with the start. Towed it home and checked it out. It is a 73 2.0 with FI.

The pump runs when I jumper directly to the battery. I have continuity from pump connector to the #13 pin on the relay board. If I jumper from the fuse to the #13 pin, the pump comes on. The fuse is good.

I have replaced the main power relay and the fuel pump relay with known good ones. With the ignition on, when I remove and reseat the main power relay, I can feel the relay click but I do not hear the injectors click nor do I hear the fuel pump start (I got this test from Dr. 914's Tech Tips).

On the fuel pump relay socket, I have power at the 30 pin and also the 85 pin. When I jumper to the 87, it does not turn on the fuel pump.

I don't know if it is related, but I have the same problem with the heater blower relay also. I jumpered 30 to 87 and I do not have power. I am not sure but I think the car died when I had the heater blower running.

I'm stumped. What do I check next?

[Tom]

Jumpering pin 87 of the fuel pump relay is the same as jumpering pin 13 of the 14 pin connector to power. You say pin 13 to power makes the fuel pump work. Try jumpering the fuse to pin 87 of FP relay. Pump should come on. If not, you have a problem with the fuel pump relay socket to relay board traces. Try cleaning the fuel pump socket with a small wire brush or rolled up fine sandpaper.
Here is a different pic of the relay board.
Tom

[warrenoliver]

Tom,

When I jumper from the fuse to 87 of the fuel pump relay, the pump comes on. That really makes no sense to me since the 30 pin for that relay also has 12V but when i jumper from 30 to 87 - no joy. What gives?

Jumpering pin 87 of the fuel pump relay is the same as jumpering pin 13 of the 14 pin connector to power. You say pin 13 to power makes the fuel pump work. Try jumpering the fuse to pin 87 of FP relay. Pump should come on. If not, you have a problem with the fuel pump relay socket to relay board traces. Try cleaning the fuel pump socket with a small wire brush or rolled up fine sandpaper.
Here is a different pic of the relay board.
Tom

[warrenoliver]

I tested the heater fan circuit also. The fan runs when I jumper from the fuse to the 87 pin. It does not run when I jumper from the heater fan 30 pin to 87. Both the heater fan blower and the fuel pump relays get their power from the power supply relay (I think), but it still doesn't make sense why I can't get either one to turn on from the 30 pin of their respective relay.

[Dave_Darling]

Both the heater fan blower and the fuel pump relays get their power from the power supply relay (I think)...

Your thought about the fan and pump relays being powered from the "power supply" relay matches the diagram above, so it should be correct.

... but it still doesn't make sense why I can't get either one to turn on from the 30 pin of their respective relay.

It makes sense to me. A relay is just a switch that is flipped electrically. What these do is connect pin #30 to pin #87a by default. When current passes through the coil (i.e., when you have +12V at either #85 or #86 and you have ground at the other) it flips to connect #30 to #87. That's how it supplies power; it takes whatever it is getting at 30 and connects it to 87.

So, jumper from the fuse to #87 of the power relay socket. You should now have +12V at #30 of the blower and pump relays. If those operate normally at that point, you have a good idea that the power supply relay is at fault.



....Of course, you could follow the Cap'n's advice and swap those relays for the headlight relays. That puts different relays in, and turning on the headlights will also check the relays you just swapped into them...

--DD

[warrenoliver]

Thanks Dave,
The relays are good. When i have the power supply relay in, and the key on, I have power to fuel pump relay 30. When I jumper from that fuel pump relay 30 to the fuel pump relay 87 i do not get the pump to turn on. If I jump from the fuse to the 87 of the fuel pump relay, the pump turns on. The problem is that i don't know what that means.

Both the heater fan blower and the fuel pump relays get their power from the power supply relay (I think)...

Your thought about the fan and pump relays being powered from the "power supply" relay matches the diagram above, so it should be correct.

... but it still doesn't make sense why I can't get either one to turn on from the 30 pin of their respective relay.

It makes sense to me. A relay is just a switch that is flipped electrically. What these do is connect pin #30 to pin #87a by default. When current passes through the coil (i.e., when you have +12V at either #85 or #86 and you have ground at the other) it flips to connect #30 to #87. That's how it supplies power; it takes whatever it is getting at 30 and connects it to 87.

So, jumper from the fuse to #87 of the power relay socket. You should now have +12V at #30 of the blower and pump relays. If those operate normally at that point, you have a good idea that the power supply relay is at fault.



....Of course, you could follow the Cap'n's advice and swap those relays for the headlight relays. That puts different relays in, and turning on the headlights will also check the relays you just swapped into them...

--DD