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Hi Folks:

A member of my Ford club picked up a 67 standard Cougar that had been in storage for 20+ years. The gas tank was rusted so he replaced it (16 gal), a new sender, and screws around the perimeter. Throws in 4 gals of gas and the gauge barely leaves empty. So I (being younger) crawl under the back and ground the gauge wire to the sender pipe and the gauge goes to full.

Next I take the old rusted sender and get the arm moving and hook it up under the car. Every position I move it to the gauge responds correctly. So bad new gauge. He buys another from a different vendor (different manuf.) and we hook it up under the car and it reports correctly to the different positions.

Drain the tank and replace the new sender this time I made sure he had it aligned properly so the float would be level. Hook it up and 4 gals of gas and the same position, barely off empty. Added 4 more gals and it moved between empty and 1/4. Hook the removed sender up under the car and the gauge works fine.
Another club member decides the instrument regulator is bad so he takes the dash out and changes it, no difference.

We even ran a wire from the sender tube to the battery negative and no change. This circuit is so simple but we're baffled.

Has anyone had this problem or more ideas?

Thanks
Jim
 

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Is it possible the tank itself isn't getting ground? Isn't the ground on the sender the connection to the tank? (not a wired ground..)Maybe try running a good solid ground from the tank to a solid frame spot...?
 

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I don't see a problem, four gals. of gas in a M/T tank will only move off slightly, four more takes it to 1/4 of a tank sounds about right.
 

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I don't see a problem, four gals. of gas in a M/T tank will only move off slightly, four more takes it to 1/4 of a tank sounds about right.
It's a 16 gallon tank. The first 4 gallons put into it should be 1/4 tank on the gauge. The second 4 gallons put into it should bring it up to 1/2 tank.

As to the original posted question, I am not very up on electrical issues however here are a few of my thoughts. I don't think that the tank gets a ground by being bolted into the car. The original mounting of the tank always has a black rubbery sealer between the tank flange and the body of the car and there is a gasket between the filler neck and the body. I would think that the sealer and the gasket would make getting a ground difficult. Please correct me if I am wrong here. One thing that does come to mind would be the condition of the plug on the wiring harness that connects to the sending unit. Sometimes the metal terminal that is inside the boot gets corroded, sometimes it gets pushed back into the boot too far to make a good contact with the stud on the sending unit.

Randy Goodling
CCOA #95
 

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So Randy, what you are saying is, when the gas hand is on empty, you are out of gas with no reserve.
 

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I just put a new 16 gallon tank in a 68 and also put 4 gallons in it. The gauge moved to just over the red line.
 

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So Randy, what you are saying is, when the gas hand is on empty, you are out of gas with no reserve.
Carlton,
I'm just doing the math. I suppose though that if the tank actually holds more than 16 gallons or if the sending unit is designed to operate above the full mark and below the empty mark that would affect my answer. What do I know? I'm usually just taking the cars apart.

Randy Goodling
CCOA #95
 

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Or picking them apart. LOL Happy times
 

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Discussion Starter #10
Here is an update!

The tank was drained and the new new sender was removed. Hooked it up under the car and it worked as it should. One of the guys (5 of us pondering this) put the sender in a bucket and poured
gas in until the pivot area was covered. Hooked it up under the car and it would NOT work correctly.

So we pulled the dash out AGAIN and disconnected the instrument regulator and I hooked up a 5 volt DC power supply in its place. Drum roll and cymbal crash. The gauge worked correctly.
The gasoline ghosts and gremlins must be causing a leakage from the resistor strip to ground and the instrument regulator does not source (output) enough current to overcome the effect.

The next time the owner is buying parts he will order one of the electronic regulators because they supply more current then the tiny copper wire vibrator in the mechanical one.
 

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Or picking them apart. LOL Happy times
Why whatever do you mean???? It's not my fault that when a certain car was put back together that the slots in the phillips head screws were not properly alligned. Or that the wrong style hardware was used to install a rear spoiler. Man, those were GOOD TIMES!!!!! Are you ready to do it again???

Randy Goodling
CCOA #95
 

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tehee - he just said vibrator! :>p Interesting to know what you found Kinda makes sense I guess.....in short whenever you things pulled appart it's worth the upgrade huh
 

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Why whatever do you mean???? It's not my fault that when a certain car was put back together that the slots in the phillips head screws were not properly alligned. Or that the wrong style hardware was used to install a rear spoiler. Man, those were GOOD TIMES!!!!! Are you ready to do it again???

Randy Goodling
CCOA #95
Hey, That's what it's all about, I love going to the shows, I love the cars, and talking with the people. Oh by the way, those little pickey things have all been fixed. Thanks
 

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CatHouse, I wish you were around to pick mine apart or at least help me get it right the first time. Trying hard to assemble this thing once correctly. Harv
 

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Hey, That's what it's all about, I love going to the shows, I love the cars, and talking with the people. Oh by the way, those little pickey things have all been fixed. Thanks
That's for sure. I really enjoy the shows and the cars but that does not compare to all the good friends that I have made over the years.

Randy Goodling
CCOA #95
 

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CatHouse, I wish you were around to pick mine apart or at least help me get it right the first time. Trying hard to assemble this thing once correctly. Harv
Harv,
If I were closer I would gladly come over to offer my help. But while I cannot be there in person I will gladly offer any help that I can here. There are also a lot of other members here that are very knowledgeable. Most all of them are more than willing to offer their help. You can also access the CCOA judging rules on the CCOA website if you are trying to restore your car to those standards. They most likely will not tell you everything but they should give you a decent idea of how we judge a car and what we look for. Any time that I can help just let me know.

Randy Goodling
CCOA #95
 

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Here is an update!

The tank was drained and the new new sender was removed. Hooked it up under the car and it worked as it should. One of the guys (5 of us pondering this) put the sender in a bucket and poured
gas in until the pivot area was covered. Hooked it up under the car and it would NOT work correctly.

So we pulled the dash out AGAIN and disconnected the instrument regulator and I hooked up a 5 volt DC power supply in its place. Drum roll and cymbal crash. The gauge worked correctly.
The gasoline ghosts and gremlins must be causing a leakage from the resistor strip to ground and the instrument regulator does not source (output) enough current to overcome the effect.

The next time the owner is buying parts he will order one of the electronic regulators because they supply more current then the tiny copper wire vibrator in the mechanical one.
I have the exact same type of symptoms with the new tank and sender I installed in my '68 XR7 a couple months back. I suspected that the voltage regulator should be replaced as a matter of course, since that's one of the things that can be made much better today than 44 years ago. I'll give that a shot before trying my backup plan-- adding a resistor to the circuit to get it to read more accurately. Right now when my gauge says the tank is full it actually is full. But then it burns down to below the red empty with about half a tank left. I'm working around it by using the trip counter on the odometer but it sure would be nice if full meant full and empty meant empty, not half full.
 

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Discussion Starter #19
New electronic regulator from Virginia Classic Mustang fixed it!
 
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