Very frustrated with not knowing how much fuel is in the tank!  I have a stock 1982 Vette. The sending unit went up and the fuel gauge went pegged to full. I replaced the sending unit, all small gauges and the circuit card. The tank is near empty but the gauge is still at full and barely moves. If the gauge was at empty and moved up just a little then it would be accurate.  Also, I noticed the insulators are color coded, green, blue or all white. Does that matter in the operation on the gauge?  All the rest of the small gauges are working fine.

Any ideas would be greatly appreciated

Thanks

Bob

|UPDATED|11/19/2018 7:31:25 PM (AZT)|/UPDATED|

If I was having this problem, the first thing I would do is pull the sending unit back out and check to make sure nothing got dislodged when it was put in. They are a tight squeeze to get in if it was done with the tank still in the car.

Then if everything looks ok I would disable that electric fuel pump, next (with the sending unit in hand plugged in) turn the ignition key to on and slowly move the sending unit float up and down to see if there is any corresponding movement on the fuel gauge.

Make sure the strainer sock isn't close as to possible interference with the float.

If by "insulators", you mean the things that go across the terminals on the back of the gauges, then yes...those are actually resistors, and the different colors represent different resistance values. They are used both for calibration, and to keep the gauge needles from moving too quickly....like a buffer.

Another thing to consider is the bladder inside the fuel tank. If it has deformed, it can contact the float on the sender, and keep the fuel gauge from reading the proper amount, the same way as if it were contacting the filter sock, as Daryl mentioned.

Great advice. I am going to try and spend some time in the garage within the next two days to see if I can fix this problem. I love this club!

Joel,

I forgot to ask, do you know if I need a specific color coded resister. I did some measurements and the green and blue appear to be about 5 ohms. The one with is not color coded shows up as a short with the VOM so I suspect it really is providing insulation/isolation between the two terminals.

My understanding is that the gauge clusters are tested on assembly with fixed instrumentation, and the resistors are used according to what values are needed to provide an accurate reading. Different gauges used different resistors....most were able to use the same resistor value, but some needed more/less to provide the accurate reading....just depended on the individual gauge. I can't say which resistor would be needed for any particular gauge for that reason. If you have a bad resistor, the best solution is to replace with one of the same value.
Are you testing these things with them bolted on to the gauges? That will not give a true value of the resistor, since you are adding in the resistance of the gauge itself. The resistors should be measured OFF the board.
To test the fuel gauge & wiring, unplug the sender unit, and turn the key on. The gauge should peg FULL. If it does not, then you either have an issue with the wiring, or the gauge itself. If it does peg, your problem is with the sender unit, whether it is bad, or it is hanging up inside the tank..

This should help

Joel is correct the meters are shunted (i.e. resister in parallel with the meter winding) I used to do meter repair and shunted meters all the time to make up for the differences in the meter winding.

Of course this was precision meters 1/2 percent to 1 percent meter movements and it was 37 years ago. 

You could use any resistor as a shut I have no idea what the wattage is but I guess I could still figure that out.  We used to use resistance wire and make our own.  This is not that critical of a measurement as I was working with so close would be good enough. 

  

I checked the net and did not find a source for the shunts nor a good source for resistance wire.  But there has to be one out there somewhere.

I know this is an old thread but my 82 is having a similar issue. After leaving me stranded in a busy intersection, my car was out of gas with the gauge showing a 1/2 tank. I then replaced the fuel pump/sending unit but now the gauge drops as fuel is consumed but when I fill up the gauge won't return to full. I've removed the sending unit twice to check it. I can leave it plugged in and watch the gauge thru the rear window as I move the arm over the resistor. The gauge moves smoothly from full to empty perfectly. I even dropped it into a large bucket of water to insure the float moved smoothly up and down as it was raised and lowered. I'm convinced the problem is mechanical and not electrical but i'd appreciate any suggestions.

With the sending unit out of the tank, look down into the tank and make SURE the badder is not deformed, especially toward the front. It doesn't take mush to hang the float up(or down).

|UPDATED|11/19/2018 7:31:55 PM (AZT)|/UPDATED|