Strange Fuel Gauge Behavior

[Mpgeslak]

Hi All,

I am having trouble with my fuel gauge.

It was working fine until I removed the main instrument cluster to replace the glass.  When I replaced it the gauge was stuck on 1/4 tank and the needle didn’t move, even when I turned the car off or disconnected the battery.  I removed the cluster again and cleaned all the contacts and when re-installing I noticed the following strange behavior:
-  If I make the thumb screw that attaches the whole lighting/power unit to the cluster tight the needle will go up but then get stuck and not move, even if I disconnect the battery
-  if I leave the thumb screw loose it moves up when I turn the car on and goes down when off.   Seems to go to the right level, but can’t be 100% sure until I drive it and see if the needle moves.

This makes no sense to me as the only thing that gets impacted by tightening the thumb screw are the three power connections between the gauge and the lighting/power unit.

Any thoughts would be appreciated!

[Pawel66]

It may be shooting from the hip, but what I once experienced was that the mechanical tension on gauge housing plates affects its work.

You may check that if the search for electrical issues fails.

[Mpgeslak]

Thanks Pawel.  The whole thing is very strange.  It does seem to be mechanical as there is no electrical reason for it to stay at 3/4 when the power is disconnected.

Any other thoughts welcome, I hate to put the dash together without being confident it is fixed!

[Mpgeslak]

Update on trying to diagnose the problem:

-  first I removed the fuel sender, cleaned it out, and with it out I used it to test the gauge.  With the thumb screw loose, the gauge operated as expected when I tilted the sender and the empty light came on when the sender was upright.   So the sender is not the problem.

-  I removed the fuel gauge and tried to recreate the needle not moving when there is pressure and couldn’t recreate it.  The needle moves freely with no restrictions.

There is no obvious restriction of the needle with the gauge installed and not sure why pressure would impact the electrical operation, particularly since it stays stuck with the power fully disconnected

Any thoughts appreciated!,

[Rick Katucki]

I think that Pawel66 is on the right track- something to do with the housing distorting when you tighten the screw. Maybe try connecting the power leads together without using the post and thumb screw to see that affects anything.

[Mpgeslak]

Thanks Rick, I will give it a try. 

The thing is it starts behaving this way without it being very tight, a small extra turn and it starts doing it.