mytrplseven

My fuel gauge is indicating full when there's only 1/2 tank and when there's no fuel in the tank and the low fuel warning is on, the gauge shows 1/2 full. The fuel level sensor was checked and it's indicating proper gradient of resistance and the grounds under the dash have been cleaned and I still have the issue.

I noticed that there's a potentiometer next to the gauge itself and wanted to know if that's an adjustment for calibrating the gauge. I have an extra gauge (white face) and could compare the two.

Any ideas?

kens_74911s

I would swap the spare gauge in just to see if the results at needle are similar I guess this is a 944-1 (early) car you are working on ? Cant hurt to tweak that potentiometer just keep track of where you started turning. I have two early gauges and don't see that pot. maybe you have opened up a late cluster? The spare gauge should lead you to determine if you need to pull the sender or not.

Inside these level sensors the float travels along a metal rod and has two contacts to the sides. two thin wires run on each side of the main rod and the resistance varies based on distance from the ends. I have seen the center rod get rusted up and then the float will bind up on the rod due to the rust crud. It does not explain the 1/2 full reading with the reserve light on though. From what I remember when the float is fully down it contacts the base and resistance is at its greatest and that triggers the light as its only a two wire circuit for level/reserve.

If you pull the sender there is a small hex nut on center of the bottom that needs to be removed sometimes its cruded up and hard to tell its even a nut as its very small, maybe 7mm. Once its off you can pull the lower section off and I think another nut then you can pull the cover tube off and inspect the main shaft and float. Just don't get two heavy handed as two the small resistance wires are tensioned and crimped in place to each side of the main shaft.
K

mytrplseven

Thanks for your input. It's a late 944 and I pulled the sender unit and it tests perfect with no hangups and all the contacts show a gradual increase in resistance as they move across the wires. I cleaned the grounds under the dash and I'm convinced that either the needle has moved on the shaft or possibly the resistor next to the gauge movement has changed value (hence the trimming resistor). I'll get to it a bit later as the Holidays are intruding with my project schedule. Waiting for a Speed sensor female connector to come in the mail so I can get that repaired. Just finished re-doing the entire top end of the 951's engine, including a rebuild of the steering rack and the turbo. 951's are a lot more work than N/A's. Happy Holidays.