The "check engine light" has come on 6 times since my 2008 ford expedition limited was purchased in february 2008, requiring a trip to the dealer each time. exhaustive checks by ford service personnel initially centered on the gas cap, however, even after the gas cap was replaced, the same symptom occurred several times. only after a determined inspection by ford service personnel was the trouble diagnosed as a faulty fuel tank which provided a poor sealing surface for the fuel pump o-ring. the fuel tank was replaced, and the trouble disappeared. *tr