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> Fuel pump shorting out, help me find the short
pgeorgeson
post Nov 23 2011, 04:24 PM
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The good news: I got the fuel pump working.
The bad news: It keeps blowing the fuse.

I am fairly certain that the pump not the problem. I think I have a short.

I have checked the fuse panel and cleaned up all the contacts there. The main harness looks fine as it goes into the tunnel and comes out of the tunnel in the engine compartment. I have checked the wires coming off the main harness to the pump. The plug to the pump looks fine. From what I can see of it, the wires also look good behind the dash. I am thinking the short may be in the tunnel.

Any specific ideas of where I should look for a short that I haven't looked for already?

If it is the tunnel, is there any way to check for a short in there other than pulling the entire harness out?
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ejm
post Nov 23 2011, 04:55 PM
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Assuming you are running stock fuel injection I would check the wiring to the auxiliary air regulator which is also powered by the fuel pump circuit. If the wiring looks good unplug the AAR and see if the short goes away.
A stock '74 would have the pump in the back and none of the associated wiring goes thru the tunnel. If the pump has been moved up front anything is possible.
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pgeorgeson
post Nov 23 2011, 05:12 PM
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QUOTE(ejm @ Nov 23 2011, 03:55 PM) *

Assuming you are running stock fuel injection I would check the wiring to the auxiliary air regulator which is also powered by the fuel pump circuit. If the wiring looks good unplug the AAR and see if the short goes away.
A stock '74 would have the pump in the back and none of the associated wiring goes thru the tunnel. If the pump has been moved up front anything is possible.


The pump is in it stock location in the right front of the engine compartment.

Please excuse my ignorance (and be gentle with me). From what I can see, the wires for the pump are joined with the main harness that plugs into the front of the fuse panel (on the left side of the front of the engine compartment). That harness then runs down and along the bottom of the front left side of the engine compartment, then appears (although it is difficult to tell) to go into a hole in the bottom front middle of the engine compartment and into the tunnel. It appears, then, that the harness then also comes out of that same hole and then goes around to the other side (right side) of the engine compartment.

I was assuming that because the fuel pump is switched to the ignition, then the fuel pump wiring ran from the fuse box, through the tunnel, up to the dash, to the ignition, and then back through the tunnel to the engine compartment and to the pump.

Am i wrong? Does all the wiring for the fuel pump just run from the left side of the engine compartment (from the fuse box) across the bottom to the right side of the engine compartment (where the pump is)?

(I would note that all the wiring that I can see in the engine compartment looks fine).

In any event, I will check the Aux. Air Regulator.
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Cap'n Krusty
post Nov 23 2011, 05:48 PM
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You are, indeed, wrong. The pump wiring comes from the regulator plate on the left side of the engine compartment.

The Cap'n
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pgeorgeson
post Nov 23 2011, 05:50 PM
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QUOTE(Cap'n Krusty @ Nov 23 2011, 04:48 PM) *

You are, indeed, wrong. The pump wiring comes from the regulator plate on the left side of the engine compartment.

The Cap'n


It certainly isn't the first time and won't be the last. Thanks.
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underthetire
post Nov 23 2011, 07:12 PM
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Doesn't the blower motor fan run off that fuse as well?
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TheCabinetmaker
post Nov 23 2011, 07:28 PM
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I agree with ejm. Aar cinnection is shorting against the block.
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pgeorgeson
post Nov 27 2011, 10:31 PM
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So the AAR was unplugged and the white wire was resting on the block. I plugged it in and taped the connection and it stopped blowing the fuse.

However, after running for a few minutes, it died. Some further diagnosis and now the fuel pump is not pumping fuel out. Again. (I was having this problem earlier, but it started working after I took it apart, cleaned it, and put it back together).

I feel like I am just chasing my tail. (IMG:style_emoticons/default/headbang.gif)
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Dr Evil
post Nov 27 2011, 10:40 PM
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As someone mentioned, the blower motor also get power from that circuit.
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pgeorgeson
post Nov 27 2011, 10:55 PM
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Blower (on front ride side of engine compartment) is now running all the time since I plugged the AAR back in. Coincidence? How do I turn it off? (the slide on the dash is all the way to the left)
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underthetire
post Nov 27 2011, 11:13 PM
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QUOTE(pgeorgeson @ Nov 27 2011, 08:55 PM) *

Blower (on front ride side of engine compartment) is now running all the time since I plugged the AAR back in. Coincidence? How do I turn it off? (the slide on the dash is all the way to the left)


Its the red knob lever between the seats that controls it.
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pgeorgeson
post Nov 27 2011, 11:39 PM
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I made sure the red lever was all the way down, but the blower is still running.
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SUNAB914
post Nov 28 2011, 11:22 AM
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Pull the heater knob control and clean the ground, fan should stop running in off position. Hopefully it will help your other problem.
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914_teener
post Nov 28 2011, 07:22 PM
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QUOTE(SUNAB914 @ Nov 28 2011, 09:22 AM) *

Pull the heater knob control and clean the ground, fan should stop running in off position. Hopefully it will help your other problem.


Get yourself the wire diagram on this site ........I think there is also one on the bird board and onein the Hayes book. I had this problem a couple of years ago and it was multiple issues.

Cracked wires at the fuel pump and a bad pin connector at the harness to regulator plate. You need to eliminate each circuit first otherwise you will be chasing your tail. You could have different problems than I ............you need to systematically work each wire.

Good luck
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pgeorgeson
post Dec 1 2011, 12:03 AM
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QUOTE(SUNAB914 @ Nov 28 2011, 10:22 AM) *

Pull the heater knob control and clean the ground, fan should stop running in off position. Hopefully it will help your other problem.


I pulled he heater knob and cleaned the wire connection and the little copper half-sphere on the switch, but the blower still wouldn't turn off. Further, even when I unplugged the wire to the switch, the blower still kept running. The blower turns off when I unplug it at the blower itself, but I can't get the switch under the knob to do anything. What am I missing?
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Dave_Darling
post Dec 1 2011, 12:15 AM
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The switch grounds the wire that goes to it. That triggers the blower relay on the relay board, which sends power to the fan.

The wire is probably shorted to ground somewhere.

--DD
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