Auxiliary Fuel Sending Unit ??

[Supermike]

Hey folks...

So after I got the auxiliary fuel tank cleaned out in the CS, the fuel gauge was stuck on empty, even though I knew the tank had gas in it.

BEFORE I had the tank cleaned, it had read "full". So under the truck I went with a piece of sandpaper and cleaned the contacts on the sending unit. Back to the cab, turn the key, and... now it's FULL again. Only this time, I know the tank is NOT full.

I've read the write-up on the sending units and testing the OHMs, etc. Only I'm not sure that's the issue. I DO know it's getting juice, though, as it went from reading EMPTY to FULL.

Does anyone know if the fuel sending units for the early 70's under-the-bed tanks are the same as they were on the '67, or if they are interchangeable? How complicated is it to change out the sending unit? Do I have to empty the tank first?

[fordman]

you might have to empty the tank yes. the sending units come out pretty easily. with just a puch and hammer. you have to turn the ring and it will release the unit from the tank. and i just checked the lmc catalog. or both of them that i have. the dent side fuel sending unit part number is the same part number for our trucks. so the sending unit is a direct swap. it sounds like your dash guage m iight be reading wrong. i would try to adjust your ipvr behind the guages. you can also remove the sending unit and move the lever to see if it makes the guage move that would tell you for sure if its the ipvr adjustment or not.

[Supermike]

Well... the gauge reads fine for my main fuel tank... empty is empty, and full is most definitely full. That's why I figured the problem must be at the sending unit. If I adjust the ipvr for the gauge, won't it screw up the reading on my main tank?

Those sending units are not that outlandish, price wise... if the part #'s match up, I'll probably try replacing it unless someone has a better idea. Seems most people complain about it not reading full, as opposed to being near-empty and reading full. It may not be a bad idea to fiddle with it and see if I can make it move, but I'd want to have the replacement on hand just in case.

This will most likely be a project for a warmer day...

[fordman]

yea its kind of cool here today. the snow is tring to melt. slowly. i think i would test the unit out of the tank before i made any decicions about replacing it. maybe the wires are shorting over or something. it could be a bunch of small things wrong that might not be found until its pulled out and looked at. those sending units have a small coil of wire inside of them. and the unit has the float and arm. on the arm is a contact like a set of points but only half of the point is there. if the wire is broken it wont send any thing to the guage. i tcould be that the sending unit has jjust stuck too. you never know.

[Nausea]

I need a replacement also - will be ordering from LMC (somehow they cost less than everyone else for this part, $50).

BTW, that locking ring needs to be turned CCW to remove. Under the locking ring is the sender plate and under that is a seal (will need new one).

According to Ford's shop manual, the sender should read 8-12 ohms with float against the full stop, 60-86 ohms against the empty stop. Of course, the gauge is 'expecting' 10 to 73 ohms. Also 'according to Ford', if the sender is off, it should just be replaced.
Have you checked the gauge selector switch? Maybe its 'noisy' or is open/shorted on the aux position?

[Supermike]

Have you checked the gauge selector switch? Maybe its 'noisy' or is open/shorted on the aux position?

Well... I guess it could be something between the aux switch and the tank, but that switch works fine when it's on "Main". Not sure why it would short over on Aux, but I'll check it out.

[Supermike]

I'm still trying to figure out my original question... from the depths of Keith's documentation, I found this picture. This makes me wonder if the "68-69" sending units listed by the likes of DC will work in my 67? Does it matter, or was it just a design change? Or, what about the sending units for the 73-78's?

[fordman]

the dent side ones look like the 68 and up ones. i dont know about the 67 nos one. i have never seen one or those tanks. so i cant direct you on that. the dentside tanks have the sender enter through the side of the tank. where does yours enter the tank? from the top or side? or is it catty cornered in the tank?