My 93 has two, one on passenger side just ahead of the can, and the other on the left side around the manifold. Which one could effect the fuel mileage. Just lost about 3 mpg, but no check engine light is on. Runs great. :confused I noticed the avg. mileage on the display went from 20+ to low 17's. No change in driving habits or driver. Maybe the gas of today, I do use the 93 octane.