1956 Buick Fuel Gauge

[Beemon]

This has been bothering me for quite some time, and being without a sufficient cash flow to tackle my larger projects, I feel this can be accomplished relatively easy (though usually not the case). I have resealed the gas tank and replaced the sender. The sender works great when the gauge wants to. During normal operation, the guage on full reads half a tank, sometimes more and rarely at the full mark. My refill habbits tend to be when the gauge pings a little lower than half a tank, which is interestingly only 6-8 gallons, which I know is not half a tank. When I had my speedometer rebuilt, I tested the gauge first by unplugging it and then touching the contacts to the connectors (not plugging them back in) while the switch was on, and the gauge worked correctly, reading the correct amount flawlessly. I would then reconnect the wires, the gauge worked fine, turn the key off, turn the key back to on and the gauge would only go up half way.

 

Is this a grounding issue with the gauge or the sender? I wouldn't think either since the gauge works as intended when the wires are disconnected and reconnected. I even took sand paper and scuffed up all contact surfaces really well to make sure there wasn't any grime to prevent contact. When the wires are disconnected, the gauge pointer disappears into the full area, so I think the ground is fine. The only thing I can think of is the leather ground strap on the sender itself isn't grounding properly or not at all and is causing a resistance, but I don't see how that's possible.

 

Any help in this area greatly appreciated!

[Airy Cat]

I have the same problem with my '56 Century. When the gas tank is full, the gauge reads about 5/8 full. 

[Leif Holmberg]

This`s how the fuel gauge looks inside,and I`m sure 95% of the gauge problems depends on the bad conetact inside the gauge.(To check the fuel sender on the fuel tank is easy to do with an OHM-meter).When I had problem with my fuel gauge I just put my hand inside the dash and tuched on the contact skrews,maybe 1/32 left and right with the ignition ON,then can can see if anything happends on your fuel gauge.

Leif in Sweden.

Edited December 6, 2015 by Leif Holmberg (see edit history)

[JohnD1956]

+ 1 for similar fuel gauge eratic movements. In my case it will usually read full till there is a half tank then it drops to the half way mark.  When it is full it always reads full. When it is half full starting ignition can result in a correct reading or empty. Drive for a while and it's sure to distract, so I just fill it up again.

 

Often times I have to wonder if the problem is in the 12 volt supply.  If I recall correctly that comes off the ignition switch.  I am thinking the problem is really in the ignition switch itself, whatever leads that circuit to be powered when the key is rotated.  I have never had an ignition switch apart though so this is just my personal theory.

[Leif Holmberg]

JohnD1956.If you are looking at the electric wire diagram,in my opinion if it was a switch ignition problem there should be a lot of other problems at the same time,neutral switch,fuse box for example.

Leif in Sweden

[Ttotired]

Beemon, I cant quite understand all of your post, but I will have a go at this

 

There is no leather earth strap, leather will not conduct electricity, but there may or may not be an earth wire to the sender, most old cars didnt have them

 

Look at the sender and see if there is 1 or 2 wires to it (normally only 1), if 1, then there is no earth to it and it is relying on contact on tank straps or whatever is holding the tank on and also screw or spring pressure for the sender to tank (remember, there is a seal between the sender and tank), so lots of places to loose an earth

 

Mopar got the right idea (eventually) and came up with this, it clips onto the fuel line to bridge over the fuel flexi at the sender

 

http://www.ebay.com/itm/Mopar-57-58-59-60-61-62-63-64-65-66-GTX-valiant-dart-grounding-strap-fuel-tank-/310537543621?hash=item484d7adfc5:m:mPNrJIfpgz22aBbzZGdVO5w&vxp=mtr

 

Good thing is, this is easy to also solder a wire onto that can then be bolted up to a good clean earth point on the body somewhere

 

This is a bit general, as I am not familiar with your car exactly, but the other thing to check is if your fuel tank is chassis mounted, make sure there is some form of earth strap/wire going from the body of the car to the chassis, not just the body mounting bolts

 

Mick

[Beemon]

This`s how the fuel gauge looks inside,and I`m sure 95% of the gauge problems depends on the bad conetact inside the gauge.(To check the fuel sender on the fuel tank is easy to do with an OHM-meter).When I had problem with my fuel gauge I just put my hand inside the dash and tuched on the contact skrews,maybe 1/32 left and right with the ignition ON,then can can see if anything happends on your fuel gauge.

Leif in Sweden.

Are you saying to wiggle the contact screws until there is a proper ground?

[Leif Holmberg]

Yes,wiggle but very carefully,I did that on my gauge and it worked,with the ignition on you can see directly if it works or not.(but no rings or clock on your hand with the hand behind the dash.)

Leif in Sweden.

[JohnD1956]

I looked at the electrical schematic and agree with Leif. If the ignition switch was bad a few other things would also be erratic.

I am no expert on electrical diagrams or systems so may I ask two questions?

First the round dot off the ignition wire. Does that indicate a splice? If so then that could be something to check.

Then on Dynaflow cars the positive side of the gauge has a wire going to the neutral safety switch? Besides checking the integrity of that connection, what purpose does that circuit serve?