Gauge Rage

[HIGHWAY BY THE SEA]

Ever since I got the 68 truck of mine running I have had problems with the fuel gauge . After I got the truck running the gas tank had to be replaced because it was rusty . So I got a used gas tank and a brand new sending unit from LMC. My mechanic installed it in there for me since he was already rebuilding my carburetor and he said that it worked fine. But after I picked up the truck I discovered that the fuel gauge was not working so I checked the sending unit and found the float had sunk . LMC sent me a new float and when I installed it the gage still would not work . So LMC send me a new sending unit and I installed it today but when I install it it does not work either . With the key switch in the on position and the sending unit hooked up to power you can ground it by hand and it will work . But for some reason the sending unit only works if you hold it in your hand and ground it while it is hooked up . As long is the sending unit is installed in the gas tank the gage will not move unless you almost fill it up and then it only registers a quarter of a tank or so. Clearly there is some frustrating issue going on here but I cannot figure it out .

[HIGHWAY BY THE SEA]

So so no one has any idea why my sending unit only works correctly when I hold it in my hand ? I was thinking there might be a bind of some type inside the gas tank but I cannot imagine why because it is in practically new condition.

[Ol Blue K20]

Your tank isn't grounding for some reason

[ddman6]

Try to ground the sender with a wire connected to a known good ground source. It is possible that you are missing some grounding straps and your cab has a poor ground.

Dewayne

[HIGHWAY BY THE SEA]

For some mysterious reason it will not ground like that . if I hold the sender in my hand with the pink wire attached to it and then touch the gas tank it will ground, but you install it inside the tank it will not .

[Tinkermc]

I must agree you have a ground problem.

[Lee H]

You should have cab to engine and cab to frame grounds, are they intact and nice and cleanly grounded?

[HIGHWAY BY THE SEA]

As best I can tell the tank is grounded. The gauge registers correctly when I touch the sender to the tank when I am holding the sender. But NOT with the sender installed in the tank. Weird mystery! And frustrating. I have to keep a gallon can of gas in the truck in case I run out.

[hayhauler71]

This may seam stupid but my new sender float arm was bent wrong had to dump 10 gallons in tank then adjust arm to 1/2 on gauge. If your gauge works grounding it to the tank your tank is grounded and not a problem

[ddman6]

You might also check for interference inside the tank.

[68gmsee]

Originally Posted by ddman6

You might also check for interference inside the tank.

This is what I was going to mention also. I got one from LMC many years ago that didn't work and found the float was touching the tank when installed in the tank. I had to bend it in such a way so that it would move freely without binding.

On another occasion, I got a sending unit that had defective windings and only worked in one position. When you have yours out, don't just ground it but using a volt/ohm meter, see if it goes up and down in resistance with the meter in ohmsX1 setting.

[HIGHWAY BY THE SEA]

I no longer think it is a ground issue. When I ground the sender with a second source it still does nothing in the tank. And when filled up the gauge goes to 1/4. So it must be an internal logistical problem. Am taking it to a friend who has ohm testing equipment tomorrow.

[68gmsee]

Originally Posted by HIGHWAY BY THE SEA

I no longer think it is a ground issue. When I ground the sender with a second source it still does nothing in the tank. And when filled up the gauge goes to 1/4. So it must be an internal logistical problem. Am taking it to a friend who has ohm testing equipment tomorrow.

If you're sure it's not binding, remove it from the tank to make sure the resistance changes through the whole range.

btw: you might want to invest in a volt/ohm meter. I can't begin to count the times I've used it on both of my trucks to check voltage and resistance when encountering an electrical problem. They're fairly cheap - ranging in price form $15 to $30 for a reasonable one.

[Andy4639]

Hook the gauge up and put a jumper ground from tank to sendor. See if it works. Then move the float up and down to see if it changes on the dash with your hand moving it. If so then it's hanging up inside the tank.

[HIGHWAY BY THE SEA]

Mystery solved. I took this to my friends house today and we removed the sending unit and he tied a string to the float rod . The sending unit was held in place by hand and he pulled on the string . It was then that we realized that the float was indeed tapping against the side of the tank causing the float rod to stop short. We bent the sending unit float rod so this would no longer happen, now the gauge does work . Next up I have to make sure it is registering correctly because I put 10 gallons of gas in there and it only registered 3/8 full. Figured it would be more than that. Now I need to caution anyone who buys a sending unit from LMC. BOTH sending units that I received from them had this same problem . So these things need to be adjusted because they are apparently made incorrectly .

[ddman6]

Way to go. Congrats on figuring it out. It is good to know that these sending units can have this problem. I've had multiple go bad over the years and have considered lmc for replacement. Thanks for the info.