gas mileage has slipped

[Bernando1]

The past four fillups have left me a little puzzled. My jeep was averaging around 17 mpg combination of city and highway. Now I am getting 15, or a little under that. I replaced the spark plugs and wires and the vehicle seems to be in good working order.
I did replace the fuel pump and filter, and now it seems like it has had a negative affect on my gas mileage. Any ideas for improving gas, I really have a wimpy foot.

[RBrandon]

Had a problem a year or so ago with my '98 grande cherokee on a trip to alabama where fuel economy went way down between fill-ups. it was followed by a check engine light and the fix was a new speed sensor. it's just a magnetic transducer on the output shaft of the tranny but whatever it's job is, it made a big difference in our case...

[Caribbean ZJ]

You fixed spark and gas so the next step would be air. New air filter and clean the throttle body. Could be a bad 02 sensor.

[CTCarpenter]

Originally Posted by Bernando1

The past four fillups have left me a little puzzled. My jeep was averaging around 17 mpg combination of city and highway. Now I am getting 15, or a little under that. I replaced the spark plugs and wires and the vehicle seems to be in good working order.
I did replace the fuel pump and filter, and now it seems like it has had a negative affect on my gas mileage. Any ideas for improving gas, I really have a wimpy foot.

Not sure what part of the country you're from, but cold weather can play a role in your fuel mileage. Here in the Northeast we were below freezing for 2 weeks straight and I noticed the fuel mileage in all my vehivles dropped about 10%.