I have a '99 XJ 4.0L, auto, NP231.
This past summer I replaced several thing under my hood. I got Bosch Platinum +4 spark plugs, new spark plug wires, distributor cap & rotor, a Red Top Optima, a Rusty's Airtube with 6x9" K&N cone filter, and a Flowmaster 40 series exhaust.
My MPG didn't seem...