no fuel reading

[green goat]

I haven't been able to get a reading from my fuel gauge for sometime so I took it out. I have used the test light and the light comes on with the on/off switch but still no reading from the gauge. I have changed the gauge and tested the sending unit with an ohm meter and not sure where to turn now. Any help would be appreciated

[george walker]

Have you checked the continuity of the wire from the gauge to the sender? And to really test the sender you need it out so you can move the float arm an watch for the changes in resistance, also looking for opens, as you move it throughout the entire range of motion. An lastly the tank needs to be grounded to the frame. If that all checks out the gauge is at fault.

[brute4c]

Good info there George...that is where to start.

Also note that there is a groundwire from the top of the tank to the frame...check to make sure you have no corrosion at the frame end and that you have continuity through that ground wire.

The drivers side frame rail area, right where the frame angles by the tank, is an area where the wire bundle going to the rear, including the fuel sending unit wire, is known to chafe...some, like mine, have chafed through 1 or more wires at that point...mine caused brake and tail light problems...could be the reason for your problem...

[kwai]

I had just the opposite problem. Ran out of gas with the gauge reading full. Not sure where to start looking for that problem.

[george walker]

The same thing applies. The fuel gauge system is very simple: power enters the gauge through the spider harness behind the dash, then it moves through the gauge down the other wire to the sending unit, flows through the sender to ground, the float arm moves up an down windings changing the resistance to ground(the wire from tank to frame). ck for power at gauge then ck the wire from gauge to tank unit for continuity and short to ground, last test the sender w an ohm meter to see that there is a good even change in resitance through its range of movement. If you have power to the gauge the wire to sender is good and the sender test ok ,you have a good tank ground the gauge is left as the culprit
when performing the tests its best to use a voltmeter instead of a test light since a test light may still light even though there is a low voltage present a voltmeter will show accurate voltage avilable.

[rpgdeity]

Alright, I'll add to this topic. My gauge "waves" back and forth like +/- 20-30 degrees in its place when I'm driving around and the fuel is sloshing. I can kinda gauge if my tank is full, 1/2, or near empty, but it always wanders back and forth. I'm assuming something is wrong and its being super-ultra sensitive to the signal being sent from the sending unit. What affects this? I heard that gauges come in different ohm settings, is this true? What about my gauge being 12V? Is the sending unit calibrated for a 24V gauge?

[moosejr]

My first suggestion on your "waving" guage, is a flaky ground wire, so you have two things causing variation of resistance in the circuit, the float, which is supposed to, and then the wire moving around a little loose on either the tank or the frame, causing more fluctuation in resistance. . these intermittents are the toughest to find, . . .good luck!

[green goat]

I have tested the ground, the sending unit with ohm meter, the wiring from one end to the other and the gauge. Just to to double check the gauge I put in the new one and it makes no difference. I have decided it must be the sending unit, since I can't get a ground out of it when I touch the body(steel bar that holds the reostat) or the under side of the head part. Unless this isn't intended to carry a ground it is the only thing left I think due to the inconsistancy.

[Barrman]

The fuel tank really isn't all that hard to remove. Have as little fuel as possible in there when you do it. (Gas is 8 pounds to the gallon) Unhook the two wires, lossen the filler tube clamp and use a screwdriver to push the rubber neck back a little just to break it free. Put a floor jack under the tank and run the two bolts at the top rear of the tank out. Remove the straps and let the tank down a few inches. Move it toward the passenger side a little and now make sure the filler neck is off. Then put it on the floor. Sweep, blow or vacuum the top off and unscrew the sender unit. The gasket will probably come apart but don't worry a healthy dose of RTV will do the same thing.

Remove the sender and start playing with the Ohm meter. It has been my experience that putting the sender top in a vise really helps since you have two leads to hold and an arm to move all while looking at the Ohm reading.

AB Linn, Saturn, Memhis and VPW all have new senders for the 24V vehicles. I will have to look, but the M715 sender has the same bolt pattern on top as the M35 unit. Just different arm lengths which can be solved by creative bending or a few fast welds once you cut it to length.

[kwai]

The gasket will probably come apart but don't worry a healthy dose of RTV will do the same thing.

Are you sure? I always thought RTV shouldn't be used with gasoline. It will set hard and then you never get it off.