Originally Posted by donski D
From May to November last year I averaged 19 mpg, in November I had a y-pipe fitted and the 36000 mile service.
Since then 16 mpg...... WTF???
Whats to blame ? the y-pipe or the service ??
Possibly a couple of factors.
Colder air is denser so means more fuel to maintain the AFR.
Also your y-pipe may be allowing better gas flow out which in turn means more air into engine. Again ECU may adjust fuelling to maintain AFR.
Or maybe you should just drive the thing and stop looking at the MPG?!