another fuel gauge issue

[Richard Shimmon]

I've reviewed all the gas gauge issues I could find and now I'm suspecting my gauge is my problem. I have a 1959 D 99% stock.
The following scenario/symptoms are from my morning drive.

Left my garage this morning for fun drive. My gas tank was approx 1/2 full but I noticed the gauge needle was flush on full. My gauge usually flops all around with less than a full tank. I think we all agree a floppy needle gauge is normal. About 5-10 minuets into the drive I noticed the needle began to fall toward empty. The needle was still firm. By the time I got home the needle was at about 1/4 tank. I don't think I drove more than 15 miles.

Back in the garage I began to troubleshoot : grounds, connections ect. I then noticed the needle on the gauge start drifting toward "full". Key was off..I walked away for a bit and when I returned and looked at the gauge it was back at full.

I then disconnected the green wire from the sending unit (per a greg bryan post) with the key "on" and the needle stayed on full. It was supposed to fall to empty which signifies a good gauge. Here's another bit of info: If I turned the key "off" and tapped on the gauge the needle dropped to empty. If I turned the key "on" and tapped on the gauge the needle stayed on full.

Any comments confirming or denying its the gauge. I have Leoni's wiring diagrams to check but they are at a friends.

thanks
rich 59 D Hawaii

[Paul Lima]

BTW, open circuit (the "green wire" not connected to anything) should show Full on the gauge. Connect that wire to chassis ground and the gauge should show empty.

[Dick Weiss]

Richard,

Your fuel gage sender, if it's still the original and never worked on, most likely has a sloppy shaft which allow the wiper contact to leave the resistance coil, OR the wiper blade's edge could be worn enough to give an erratic reading.

I've rebuilt several to keep the originals for the dates; Also, from the tank being empty, adding 3-gallons of fuel and checking the reading approx.1/4 level, the float's arm may need some slight bending. OH--not forgetting the condition of the float, too.

On the later B/C units, the faulty readings are caused by internal corrosion of the pivots which looses the ground.
On either sending unit, the thin internal spring blade may be corroded--I've seen a couple vblades actually fall loose!

Dick

[Richard Shimmon]

Dick Weiss. Thanks for reply. I removed the sender from tank and tested it on bench. The resistance was in normal range : approx 200 ohms when full and 6-7 when empty. We did resolder a suspect thin ground strap inside the sender. Reinstalled in tank and no change.........gauge goes flush to full. Could something be wrong with the gauge itself causing this? Wiring to gauge is correct and grounds are ok. When I remove the gauge can I bench test it? Electrical stuff and my brain don't get along.

[Dick Weiss]

Richard,

When bench testing, the float's internal wiper blade should not go to full movement; it should just move to near full travel to get the proper ohm reading, or it'll mis-read the full condition by 'bottoming out'.
Again, if the pivot shaft is a little sloppy in the ususal corroded bore, you'll get varied readings.
Be sure the coil face (for the wiper blade) is clean, BUT be very careful NOT breaking the fine wire; also check any looseness of the thru-stud--if loose, it may affect the readings.

Dick

[Richard Shimmon]

Thanks again Dick. The problem is I don't get ANY varied readings. It's either flush on empty with key off or flush full with key on. Could the fuel gauge itself be faulty? I'd like to put in another sender but don't have one.

Richard

[Richard Shimmon]

Problem solved!!! The schematic shows 2 green wires going to the combo gauge. One goes to the oil pressure switch and the other goes to the fuel tank sender. They were simply reversed! I must have jarred some wires loose when I had the windshield motor out. I was ready to change out the sender and gauge. Nice to have a simple solution even though it frustrated me for a week.

Rich 59 D
Hawaii.

[Al Zim]

All: if you are tired of your fuel gauge needle flopping around we offer an electronic device that stabilizes the needle. Part Number Zim.201.000.XX the price is $20.95 plus shipping which is about 4 dollars. Zim's Autotechnik 800.356.2964 you car order on line WWW.allzim.com thanks al

[Pascal Giai]

Mine stays stuck on empty when I turn on the ignition switch.
I have to tap the gauge to wake it up each time...
Any solution ?

Pascal