So I went on a weekend trip last weekend. When I switch to the left side tank the guage always reads full. But the guage reads fine when on the right tank. I am guessing I need to drop the tank and replace the sender.
Anybody else ever have this problem? Anything you guys think I might want to look at before I drop the tank? Thanks

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Originally posted by JoshS:

Anybody else ever have this problem?

Yup

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Anything you guys think I might want to look at before I drop the tank? Thanks

Check selector switch, ground to sender, signal to sender. A cleanup and tightening might be all that is needed.

Somewhere, there is a post by me with some details on what I found and did with my sender. A search might save you some money.

A fuel sender is a variable ground resistor that goes from (in GM gauges) from 90 ohms to about 10 ohms. Others can vary up to 170 ohms. To test just find the wire coming from the tank and ground it. The gauge should go to full. If you cut it temporarily it will go to empty (or perhaps the other way). If the wire thing does that the sender is bad and you have to replace it. If not, then it is a wire or gauge issue. It sounds like the wire is broken more than the sender.

Would be nice if it just the wire. I will see. thanks for the replys!!!

quote:

Originally posted by Tom K:
A fuel sender is a variable ground resistor that goes from (in GM gauges) from 90 ohms to about 10 ohms. Others can vary up to 170 ohms. To test just find the wire coming from the tank and ground it. The gauge should go to full. If you cut it temporarily it will go to empty (or perhaps the other way). If the wire thing does that the sender is bad and you have to replace it. If not, then it is a wire or gauge issue. It sounds like the wire is broken more than the sender.

Ok so I pulled the wire off the sender and grounded it. The guage went to empty. So this means I need a new sender right?
And if that is the case, anybody know where to find one?
This one here http://www.napaautoparts.com/C...D%28P_RecType%3aA%29
Looks exactly like mine on the top. ( I have not pulled it out of the tank yet) It says it is only for years upto 1973. Mine is a 75' barth on a 74' chassis. You think it could be a 73' fuel sender in there?

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Originally posted by JoshS:
Ok so I pulled the wire off the sender and grounded it. The guage went to empty. So this means I need a new sender right?

Usually, but not always, grounding out a wire pegs the gauge. Perhaps you have a bad ground connection? Sometimes the straps that hold the fuel tank up get a little rusty and the ground doesn't make a good connection going through the straps. Try a better ground connection.

What does the gauge do with the wire off? Does it go to full?

When you say "when I switch", do you mean you have one gauge and a selector switch like an airplane? If so, and it works correctly on one tank, then the gauge is good and at least one tank has a good ground. That leaves the sender in tank two or a bad selector. You might try switching terminals on the selector to see if the problem reverses: the other tank works fine. If so it is the selector that is the problem. You might also ground the "good" tank sender and see if it goes to empty. You won't hurt it as it is only a resistor. Most GM that I have seen read empty when resistance is near zero (grounded),

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Originally posted by Bill N.Y.:
Usually, but not always, grounding out a wire pegs the gauge. Perhaps you have a bad ground connection? Sometimes the straps that hold the fuel tank up get a little rusty and the ground doesn't make a good connection going through the straps. Try a better ground connection.

What does the gauge do with the wire off? Does it go to full?

The ground seems good. I have continuity between the ground on top of the sender and the frame two feet away.
With the wire off it still reads full.

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Originally posted by Tom K:
When you say "when I switch", do you mean you have one gauge and a selector switch like an airplane? If so, and it works correctly on one tank, then the gauge is good and at least one tank has a good ground. That leaves the sender in tank two or a bad selector. You might try switching terminals on the selector to see if the problem reverses: the other tank works fine. If so it is the selector that is the problem. You might also ground the "good" tank sender and see if it goes to empty. You won't hurt it as it is only a resistor. Most GM that I have seen read empty when resistance is near zero (grounded),

Yes one gauge and a switch to select which tank to use and the gauge reads accordingly.
I will try switching the wires on the selector switch. and see what that does.
Grounding the other tank will be a bit more difficult. I cant reach the sender on that one. It is a little higher and too close to the top. I would have to drop that tank just to get my hands on it.

Rochester Gauges in Dallas builds and restores fuel senders :http://www.rochestergauges.com/pages/PDFs/8341_70.pdf

I had them make a new on for my coach and it fit perfectly. You just need to tell them the brand and model of the gauge. Call them for help.

Ok so I pulled the selector switch out of the dash and did the following.
Pulled both leads coming from the two tanks off.
-gauge goes to full on both switch positions
Switched positions of the two wires.
-gauge still reads full on both switch positions
Put one wire on at a time and gauge still reads full no matter what.
So unless it is hooked up as it previously was (the same way it has been for years and working fine) the gauge goes to full. So I put it back together and everything is still the same. When on right works fine. When on left gauge reads full.
So since switching wires on the switch does nothing except read full could it possibly be the switch?? That would be nice vs. dropping the tank and finding or repairing the sender.

OK, so opening the circuit by removing the leads makes the gauge read full. That means when you short both wires to ground the gauge should read empty. Since the left tank reads full all the time the sender resistor circuit is open, read "broken". Time to drop the tank, or as is the case on some SOB coaches there was an access hole in the floor underlayment that was covered with a " metal saucer" that could be removed to access tank senders. Might not be much easier but you could remove the carpet or tile and make such an opening, for next time. But if you drop the tank I would have it steam cleaned and have a drain plug installed. On the Gillig the sender is side mounted so we did not have to remove the tank. The pickup tubes however were mounted on the top and the old rubber hoses were unreachable without dropping the tank.

Ya that is what I figured. There is no access plate in side and I cant really add one because the water tank is directly over the tank.
Oh well, easy enough to drop the tank. two nuts on the straps and down she comes. Probably replace the rubber hoses while I have it down also.
Thanks for all the help!!!!