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Old 09-04-2005, 08:32 PM
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Electric fuel pump bad or not?

I have a 1973 Vega that is not getting fuel to the carburetor. This car has an electric fuel pump built into the tank. I pulled the fuel pump and sending unit, out of the tank. I am getting continuity across the two terminals of the fuel pump, and I am getting current to the pump, but the pump does not work, even when I connect a 12 volt source directly to the fuel pump.

Is the fuel pump bad or is there something else I am missing?

Also how can I check the sending unit, the gas gauge does not work either?

Also discovered something really weird. I found a steel pipe about 12 inches long and about 1 1/4 inches in diameter rolling around in the bottom of the gas tank. Anyone have a clue what this was in there for?
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Old 09-04-2005, 08:52 PM
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Ground

Doc here,

Sounds like you might be missing the ground wire to both units...

Run 12 Volts and GROUND to the pump , see if it will run then, Then check the sender..

Senders are totally ground dependent...

to test the gauge, pull the sender wire, the gauge will either rise to full or drop to empty, depending on how wired..Then, ground the sender wire to the frame the gauge will travel all the way the opposite direction if working.. Hook a good ground to the sender body and try again, move the arm up and down..If the gauge does not move, the sender is bad..

How much resistance does the pump show? 000 is a dead short! Might be somewhere around 10 ohms to be correct..The pump could also be rotor locked (not turning..see if it hums and gets warm..this would indicate that. You can try to pull the sump screen and turn by hand to free it if so...But I'd replace it straight up..I'll probably lock up again.

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Old 09-05-2005, 10:07 PM
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Doc, you were exactly right about that fuel pump

When I ran 12 volts directly to the fuel pump I connected a 12 volt battery directly to the pump. Ground wire from battery to ground terminal of pump. Positive wire from battery to positive terminal on pump.

Is this the correct way to test it? I did not get any action or hum from the pump but it did get warm. The resistance of the pump was .o1 so it looks like you were correct, the pump needs to be replaced.

Concerning the sending unit test, I hooked a ground wire to the sender body, while at the same time I had a ground wire to the sender wire. Did I understand your instructions correctly? I did not get any reaction at the gas gauge when moving the arm up and down.

If that means the sending unit is bad there is no replacement available. Is there any way I can rebuild the sending unit myself?

Thank for the advise doc, you were right on the money.
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Old 09-05-2005, 10:46 PM
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Hotrodman,

Your pump sounds bad, but I am going to toss something in here just in case.

Is the fuel line disconnected? Just wanted to make sure the pump is not stalled/off because it has pressure on it and not calling for fuel.

The other thing regarding the guage. What doc meant by its ground dependent is that senders are the "ground side" of circuit. So your GUAGE is wired HOT all the time and the gauge moves up and down based on the resistance to ground. So the sender must be chassis grounded.

So to test it you can do a couple things.

1) With it out take your ohmmeter and run it between the sender wire terminal and ground ON THE SENDER. Move the float up and down and you should see the resistance changing as you do.

2)Take the wire that goes to the sender and MOMENTARLY ground it. So with the cars key on just touch it to ground for a second. Your gas guage should go full scale (one way or the other) when you do this. If this happens your gauge and related wiring is good. Then it has to be the sender.

Its odd that both stopped at once. Since they are basically independent with the only thing common between them being the ground. So double/triple check your ground to the chassis.

Rich
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Old 09-10-2005, 09:47 PM
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New pump ordered.

Great information from both of you. Thanks so much for the help. I followed your directions exactly and discovered the fuel pump and sending unit were bad but the gauge was good. I did have the pump out of the car and the line disconnected. Unfortunately as far as I know there is not a sending unit available. I found a company that would rebuild my present unit but it cost $127 which is more than I want to pay. I found out from the previous owner that the gauge and the pump did not go bad at the same time. The sending unit went out several years before the fuel pump. Also discovered it was one of the grand kids that put the 12 inch length of pipe in the gas tank. I have cleaned this tank up using my own methods. I pored two cans of Drano into the tank and filled with water and let stand over night. After rinsing that out and letting it dry, I put 20 lug nuts inside the tank and shook vigorously for 30 minutes over a period of several days. I shop vacuumed out the majority of the dry sediment, then rinsed several times with gas and it looks reel good. Tank was in good shape to begin with just dirty.
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