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Just installed a new fuel tank and sender in my 65. (66 fuel tank and sender.) I put 4 gallons of fuel in the car to get me to the gas station and the gauge reads full. Thought maybe I put the fuel sender plug on upside down, so I turned it over and still the same thing, reads full. I went ahead and filled the car up, $100.00.....ouch and it reads way beyond full. Any ideas what could be wrong? Bad sender??
Thanks.....
 

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Sounds like it may be the wrong sending unit as it operates off resistance or ohms crap i cant remember. The gauge and the sending unit need to be compatable. If it is a factory gauge find out what the resistance range is on the gauge and then match it up with the sending unit specs. They have to match to read right. It could also be a grounded positive wire most likely on the back of the gauge. Anybody care to chime in a bit. Not real strong on electrical but that is what it sounds like. Had the problem on a 74 Nova and that was the issue.
 

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If both are new, to test gauge unplug wire from sender and ground it turn key on, gauge should show full. Cant remember right off hand the resistance values for fords are supposed to be but sounds like its either the wrong sender or just needs adjusting.

a copy and paste:


  • SW - SW gauges - 240-33 Ohms
  • VDO - VDO gauges - 10-180 Ohms
  • GME - GM up to 1964 - 0-30 Ohms
  • GML - GM 1965 and up - 0-90 Ohms
  • ORG - Early Ford & Mopar - 73-10 Ohms
The lower the gas in the tank the less resistance. (smaller the number)



HTH




MRO.....
 

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Do you know what it read when it was empty? If it read full with only 4 gals in it a couple of things to check. Make sure the wire going to the guage from the tank is not pinched and making ground, then there is the instrument panel CVR{constant voltage regulator} when these go bad it usually gives a high reading on the guage.
 

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Is it a stock fuel gauge? Are the other gauges working properly?

BTW - I'd find a new gas station. A max of 21 gallons (24.5 - 4 + a little to get there) means you're paying $4.76 per gallon!

David
 

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Don't remember where utry lives now but heard gas is over $5 a gallon in CA and at the rate it's going up it won't be long for that here if it doesn't stop going!
 

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ORG - Early Ford & Mopar - 73-10 Ohms
....

The stock gauge on the 65 only takes 5v or so. There is a resistor (pic) that drops the voltage down to that but if the resistor is busted, so that you get 3x voltage, I think it will read 3x the level.

I could be wrong, but how likely would that be???
 

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Try this link. Fuel Tank Sending Unit Tech - FORDification.com

On my 65 Galaxie(new 66 tank & sending unit) the plug on the sending unit only fits one way(pretty sure). I had a problem with the sending unit. I never really got a good answer. The ground terminal on the sending unit is not grounded to the sending unit. It had an insulating washer on the backside. I assumed that the ground wire from the trunk area going to the ground terimal in conjunction with locking ring touching the sending unit was suppose to complete the ground circuit. I manully soldered a link between the two(has not blown up yet).

Anyway, with the gas level low enough, you can pull the sending unit, move the float arm manualy and either watch the gas gauge for movement or use an ohm meter to test. You can also fine tune the E/F when you get it working.

Also, testing the gauge to first verify that it is good is not too hard. However, locating the instrument panel voltage regulator and testing it in place is an adventure.

good luck.
Mark
 

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I don't know where our OP went, but a few random thoughts -

To be clear, the more power the gauge sees, the higher the needle. The ~73 ohm sender resistance at empty is high resistance (for a low gauge needle) and when full the resistance is lower (passing more power for a high gauge needle), and why it is a 73 to 10-ohm sender.

All the gauges have the same guts, e.g., the oil pressure works exactly the same way with the same parts. You can even cannibalize parts from one gauge to fix another.

Both the end-point setting and the sweep are adjustable on our gauges. Once working correctly, they can be "zeroed" for fairly accurate empty and partial readings.

The IVR (instrument voltage regulator, a.k.a. constant voltage regulator - which certainly isn't constant ;) ) can be tested at any gauge sender by probing the wires. The water temp or oil pressure wiring is more convenient. The regulator works as an ON/OFF averaging system much like a turn signal flasher, cycling 12-0-12-0. If on exactly 1/2 the time and off 1/2 the time, you would average 6+ volts or half the battery voltage. The Ford IVR is set to output an average of +/- 5.7 volts. So, if using a test light, look for fairly even flashing of the light. If using an analog volt meter, look for an average voltage. It trips on and off just fast enough you don't usually see the gauge needles wiggle.

IVRs come in many shapes and connector styles. If you can source the right version, you're golden. If not, you can convert yours to full electronic with two parts (about $2) from the local electronics store - a 5v voltage regulator and a diode. This conversion actually produces constant voltage from the regulator, and the diode bumps the output to the correct 5.7 volts. Most eBay and parts-house conversions for sale do NOT have the extra diode and the voltage is too low at a fixed 5.0v. Gauges tend to read low with them. Do your own if you or a friend can solder. Better function and way cheaper.

1937Mark isn't the only one I've heard that has had a funky replacement sender, with some having isolated grounds, and others having the leads reversed. Examine and test to verify the new one is wired and working like the old one. Save your old one until you're sure the new one is right. The old senders are usually of better quality and can often be repaired.

David
 

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Just installed a new fuel tank and sender in my 65. (66 fuel tank and sender.) I put 4 gallons of fuel in the car to get me to the gas station and the gauge reads full. Thought maybe I put the fuel sender plug on upside down, so I turned it over and still the same thing, reads full. I went ahead and filled the car up, $100.00.....ouch and it reads way beyond full. Any ideas what could be wrong? Bad sender??
Thanks.....
When you get the answer let me know. Been trying to find out why my gauge goes to full and stays for 3 years. Installed 3 new sending units. Every things says it's the sending unit.
 

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Discussion Starter #11 (Edited)
Still here...... Had to take a break from the car. Getting a bit irritated with it. I can't seem to go 2 days without something going wrong with the car. It's left me stranded twice now. (First classic I've owned.) Sent a email to the vendor and got this back.

The sending unit does not need to be adjusted. Has the gauge in the dash been replaced at any time? Also please check all ground connections. The unit could possibly be defective, but it is very rare for a unit to fail. To check the unit you can verify the ohms with a meter. The unit should read 78-0 from empty to full.
Thank you,

As soon as the fuel level drops below the sender, I'm going to remove it and check it out. The old sender worked, but had a spot that it would not read, would go to empty then back up to correct level, but would read correct for the most part.
 

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Make sure it has a good ground from the sender/tank to body of car. You may have to make up a ground wire. As my first post was referring to was to give you the values to have for testing the sender unit itself to rule out a fubared one. :confused:

Also doubt its the dash vr, if the rest of the gauges are working correctly.....



MRO.....
 
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