[threeonthetree]

My fuel gauge has not worked properly from the time I bought the car. The needle moved slightly towards full so I assumed the sender was bad.
I tried checking the gauge by grounding the lead to the sending unit. Nothing. I checked the power to the sender and had a pulse of 5 v +/-, so it seems I have power to the sender.
I recently removed my fuel tank for repair to the drain plug fitting. The tank had been sealed around the flange with a mastic/putty of some kind. I'm wondering if this putty will affect the proper grounding of the tank? I removed the sender noted the float had gas in it so I'll replace it. I tested the resistance by clipping my meter to the power and ground lead. The resistance was not consistant when moving the float. It ranged from 50 through 160 ohms or so and was erratic when moving the float arm. The float arm seemed loose, perhaps not making good contact? Should the resistance be consistant when moving the float?
Also I'm wondering why the plug connector has 3 prongs. Isn't the sender grounded through the tank flange?
I may try plugging the sender in with it out of the tank, grounding it with a jumper and moving the arm. I'm thinking this should be true test if the resistor is working.
Appreciate any help/comments. Thanks

 

[Bad69cat]

You should see variable resistance as this is what controls the needle level. The range sounds about right, so I think your OK there. I think your idea of trying it outside of the tank is a good one. Sounds like bad ground or no connection somewhere....

 

[1969XR7Vert]

The resistance is about 10 to 90 ohms, sounds like you've got a bad sender. To prove out the gauge and power to it, ground each of the two leads (one is sender, one is low fuel) of the harness connector to ground. With the sender one grounded, the gauge should indicate full or more than full. Yes, the ground is through the tank, the only connections on a LF sender are the two I mentioned and a locating non-metallic prong.

 

[sweetair]

You said this-------------? I removed the sender noted the float had gas in it so I'll replace it. -------------------Did you replace it? If not I would start there before reinventing the wheel. My fuel gauge did not work. I oened the tank and there was gas in the float. I replaced the float, put a new gasket and tank clamp on and voila, it works now. It never is FULL FULL, but gets pretty close to the top.

Strangely my low fuel light is now always on. I must have disturbed something when doing this project. If there isn't an easy fix the wire might be snipped neatly to disable it.

Good luck.

 

[1969XR7Vert]

The sender rheostat can sometimes be repaired, if you are a crafty bugger. I have on occasion fixed them back to functioning from the state you describe. Here is how you do it. Carefully unbend the tabs which hold the rheostat housing together. Then carefully separate the two halves. Examine the contact on the end of the spring arm and clean it up using fine sandpaper or a contact burnisher. Sometimes expanding the contact spring arm to increase the pressure against the wirewound rheostat element helps too but be careful, it is easy to overdo this and/or change the angle at which the contact rubs against the wirewound part and can cause binding. Be sure to work the arm and see how it feels (measure resistance min/max too) before you bend the tabs back over. So sayeth the ECI.

Regards,

Bob

 

[Bad69cat]

LOL - All hail the ECI! : Give it a shot - sounds like it's somewhat working, maybe just cruded up bit ehh?

 

[threeonthetree]

Thanks for the replies! I haven't replaced the float yet and am not confident buying a used one so I think I'll buy a sender and go from there. I grounded the leads and the gauge did not move. I pulled the dash, tested the gauge with 2 D cells duct taped together and it went to 3/4 full so the gauge is good. (I also had the clock repaired... it needed a spring clip and a good cleaning)

I'll try plugging in the sender while out of the car, running a good ground and see what the gauge does.

 

[sweetair]

That is great, BUT if you don't have a float that is not full with gas, it will NOT float, but sink, hence the gauge won't work. I believe you can get a new one from Ford.

Good luck.

Thanks for the replies! I haven't replaced the float yet and am not confident buying a used one so I think I'll buy a sender and go from there. I grounded the leads and the gauge did not move. I pulled the dash, tested the gauge with 2 D cells duct taped together and it went to 3/4 full so the gauge is good. (I also had the clock repaired... it needed a spring clip and a good cleaning)

I'll try plugging in the sender while out of the car, running a good ground and see what the gauge does.

 

[Bad69cat]

Yep make sure it's a float and not a sinker!

 

[threeonthetree]

I'm checking on a new float today and I'm wondering if I should scrape off the mastic that was sealing the tank flange to the trunk floor. It may be better to seal the edge once the tank is screwed in. Anyone know if the tanks were sealed at the factory?

 

[Bad69cat]

Here's another nice tank option to consider: http://www.mustangmonthly.com/techarticles/mump_1005_ford_mustang_scott_drake_enterprises_tank_armor_22_gallon_fuel_tank/viewall.html
I think 3M makes a good sealer that fits this scenario - should be able to get it at any auto paint supply house.

 

[1969XR7Vert]

I used 3m black strip caulk for the tank to trunk.

 

[towcat]

The correct color of the strip caulk is grey and is also used under the fender edges and is waded up and used to fill large openings under the fenders and quarter panels and other places by Ford.

 

[threeonthetree]

I dropped the float off at the local rad/gas tank shop, they convinced me they could fix it. The sealer strip looks OK, I'll likely clean it up and reinstall the tank. The sending unit tested out OK and I'm thinking of an additional ground wire on the mounting screw next to the trunk fitting if I don't get a gauge reading once everything is installed.
The tank armour looks like a great idea, maybe a project for next winter.

 

[1969XR7Vert]

Hopefully the shop won't charge you much, a repro float is $10: http://www.mustangsunlimited.com/itemdy00.asp?T1=240075+01

 

[threeonthetree]

the repair is costing me $25. Shipping into Canada incl brokerage fees and tax for a single $10 part is more than I'm paying for the repair so hopefully the repair works out.

 

[threeonthetree]

The float is repaired (it was cracked)and the sender reinstalled. I need to pick up a new filler hose. The fill opening in the tank is offset from center by 1/2" or so although it should go back the same way it came out. I'm wondering if the left to right position of the tank in the Cougar was different than the Mustang. Why the offset???..

 

[threeonthetree]

The float is repaired (it was cracked)and the sender reinstalled. I need to pick up a new filler hose, I should have known a 40 yr old hose wasn't worth saving. I'm wondering why the fill opening in the tank is offset to the right of center by 1/2" or so. Was the left to right position of the tank in the Cougar was different compared to the Mustang or could it be an offshore replacement tank not fitting correctly?

 

[Cavallino]

Since it is one of the few item on my cat that does not work, i would like to get the low fuel overhead warning light on my 67 XR7GT. Anyone selling refurb fuel sending units with the low fuel feature (hopefully with core change/exchange)?

If not does anyone have any experience with the electronic units the go behind the dash?

Thanks.