Fuel level gauge not working

[espooner]

2002 Boxster S, 6-speed, 45,000 miles.

While at Watkins Glenn Intl. last weekend, my gas gauge started acting up. It read "full" all day, when normally it is on empty by the end of the day. Turning car off and on had no effect. Filled the tank that evening (14 gallons). By the end of the first run the next day, it read 3/4 full, and was working normally. 2 hours later, it reads "full" again, and has done so since then, even after driving 225 miles back home.

My Bentley repair manual states that the fuel level sensor and fuel pump are all in one, and cannot be replaced separately. The part alone is $372 from Pelican Parts. I don't want to buy it if the gauge itself is the problem.

Before sending for one, is there any testing to do to CONFIRM that it is a bad sensor, rather than a bad gauge? It would seem that as the gauge goes full scale, and at least once read 3/4 full, that it is not the problem. Should I smack the pump/sensor with a rubber mallet to free a stuck float? Anyone have any similar experience?

All replies welcome.

Eric Spooner

[J Tinsby]

Originally Posted by espooner

It would seem that as the gauge goes full scale, and at least once read 3/4 full, that it is not the problem.

Eric Spooner

Eric,

In my years of experience with ALL cars, irrespective of brand or model the gauge itself is rarely the culprit.

In most cases the gauge is getting a varying ground signal from the sending unit. If it were I, I'd try to find the wire that is for the sender and not the power leg for the pump. I'd try grounding it solidly momentarily and have someone watch the gauge to see if it responds to a full ground.

It may only take a second or so for the gauge to go full scale, there is a damping circuit that prevents the gauge from responding to sloshing fuel. Without that, the gauge would swing wildly from full to half to whatever.

Hope that helps.