Sounds like there might be a problem with the sending unit, gauge, or wiring. Are you basing the mileage on what the gauge says? If your gauge is messing up the calculations wouldn't be right. If the mileage is down though, you could need new plugs, plug wires, or air filter (clean filter if K&N, etc). Also check air pressure in tires, if it's low you'll have less mpg. Also, did you do anything new that could have effected mileage?
Of course there's always the chance something may have caused a glitch in the computer system too. You might try disconnecting the battery for a few seconds to reset it and see if that corrects the problems...
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92 XLT Daily + Various Blue Oval at any time!
carolina_express@go.com
[This message has been edited by Carolina Express (edited 08-22-1999).]