Miles968

A couple of years ago, during a routine service, I mentioned to my mechanic that my fuel gauge did not seemed to be working correctly. It seem to stay on full nearly all the time and then drop rather suddenly to 1/4. From 1/4 to empty it seemed to work fine. He assured me that it would work better if he replaced the sending unit in the gas tank. So I let him replace the unit and it still did not work very well. I chalked it up to another 968 quirk. The other day it was getting on my nerves. I went to the gas station and filled up. When I removed the gas cap it made it's usual sucking sound taking in air. This gave me the idea that the sending unit/float may be held somewhat in place by this vacuum, very much like holding water in a straw by placing a finger over one end. Just like the straw when you remove your finger the water flows out smoothly.

The bottom line is that there was not enough air entering the tank as the fuel is consumed. My experiment was not to tighten the gas cap a firmly as usual so that more air may enter. So far the fuel gauge seems to be working much better! I have now seen, for the first time in 8 years since I have owned the car, the gauge gradually go from full to near empty!

Has anyone else experienced this?

John Etnier

I believe you're experiencing a failure of a pressure-balancing vent hose connected to the fuel fill line. You certainly shouldn't be experiencing that 'sucking' event when you remove the gas cap: you've 'fixed' the problem but haven't found or addressed its cause. Look further. Hope this helps.

Miles968

Thanks for the reply!
I'll have the line checked