Testing wires for sending unit

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Sep 14, 2002 | 05:20 PM

78bigunns

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From: Culpeper, Virginia

Testing wires for sending unit

Hey all, trying to troubleshoot my gas tank problems. I've dropped the tank and pulled the sending unit and float assembly. I tried testing the hot wire coming back to the sending unit, got no reading what so ever. Should the key be turned on for this test? The wire doesn't have any nicks or bare metal. The fuel tank (selector valve?), is that the thing halfway up the frame with the fuel line running into it? Once again, should I have key turned to "on" to get a reading? Last, could I tell anything by looking at the float assembly, namely characteristics that would signal a problem unit? Thinking of replacing sending unit anyway, I have the tank down, might as well save myself the trouble down the road. I want to reinforce that I had no problems with my fuel tank or gauge until I dropped the tank two weeks ago. What are your thoughts, thanks, Blair

Sep 14, 2002 | 05:46 PM

krazdndenver

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From: Denver

Testing wires for sending unit

Is this an in tank fuel pump?
If so you do need the key on to check if you have got power to it.
If no power check fuse and wiring from tank to ignition switch.
The sending unit works on resistance, you check it with ohm meter, as you raise and lower the float the resistance changes.
Hope this helps you.
Robert
72 F-100 Ranger XLT W/ 86 5.0L W/AOD
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Sep 14, 2002 | 10:19 PM

Mil1ion

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Testing wires for sending unit

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Sep 15, 2002 | 08:12 AM

78bigunns

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From: Culpeper, Virginia

Testing wires for sending unit

[updated:LAST EDITED ON 15-Sep-02 AT 09:13 AM (EST)]My fuel pump is the mech type that is mounted on the timing cover. I don't completely understand how this setup works,or what the sending unit does, but I figure I loosened some rust on a connection and now, no gauge reading and the sending unit doesn't appear to be working. I have no gas coming to motor, I can idle all day though. Thanks for diagram, will start chasing today. Thanks, Blair

Sep 15, 2002 | 05:20 PM

78bigunns

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From: Culpeper, Virginia

Testing wires for sending unit

O.K. Sorry for new post, wasn't thinking about it. How could I check the resistance of the SU itself? I cleaned the ground before, maybe that helped? I also tried to clean the harness plug holes, they seemed gooped up. BY different arm positions, do you mean to check it with the gauge while raising and lowering the float arm? I tried something a little while ago, hooked up SU and float assembly to the harness, turned key to "on", buddy watched gauge while I raised and lowered the float. My needle promptly rose and lowered accordingly. I'm thinking maybe the rust was on the ground, and was complicated by the goopy terminals on the SU harness. How could I check for the resistance on the SU itself? Thanks for the diagram, it was much easier to follow than the one in my faded and much used Haynes manuel. Thank you, BLair

Sep 15, 2002 | 07:17 PM

Mil1ion

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Testing wires for sending unit

From other thread :

The diagram I posted should answer that.
The sending unit gets its power from the ICVR which pulses power to the sending unit.

If the gauge pegged with the connector touched to ground,the problem is definitley the SU.

You will Now have to remove the sending unit and check it in different measuring arm positions.

It could be as simple as a bad ground or the resisitor on the unit.

New REPLY:
You can measure the resistance by removing the aluminium cover on the SU ,to access the rsisitor.

Just a head's up 78Bigunns!

You might consider purchasing the CDROM version of the Original Ford Shop Manual that's available here at motorhaven.autoanything.com

It works out to be cheaper than a paper manual on E-Bay.
Well worth the money.

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Sep 19, 2002 | 06:24 PM

78bigunns

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From: Culpeper, Virginia

Testing wires for sending unit

I recieved my new sending unit today, installed, and its working like a champ. I tried to test the resistance of the other one, but when having my tester set to the only resistance setting it didn't read anything, so I purchased the new one. Working great, thanks for all the replies. Blair