Here's the scenario The plugs in the E320 were Bosch Supers. I changed them to Bosch Platinum 4s. Fuel mileage dropped from 29mpg to 26mpg.
One hypotheseis is that the Platinum 4 plugs require more voltage and so were desaturating the coil. As a consequence, not enough spark for a good burn. Another is that they were too efficient, prompting the computer to input more fuel, thus increasing consumption.
(Last night I changed back to the Supers.)
What are your thoughts on this?
Collin KC8TKA E320/97