Any one got any ideas on the above - MPG dropped 4 - 6 MPG ( 24 to 18-20 mpg!! ) after fitting a decat downpipe ( H&S with splitter ).

Already got decat ( SS) centre and rear parts, ITG air filter in air box, Walbro fuel pump and FSE regulator, Scooby ECU, Samco hoses, Forge recirc dump valve, STi large straight TMIC, STi radiator cap, MRT inlet plenum.
Car is WRX wagon, TD04 turbo, 380 injectors as std.

Fitted OBX headers and new Lambda sensor ( from Lambda.com, sort of universal heated one, 4 wire ) shortly after and still same MPG.

Runs well, just thirsty and very sooty exhaust.


Is this normal?
Do I have a problem, dodgy MAF or Lambda, air leak, leaky injector, overpressuring the injectors ( 380's on 3.2 bar fuel pressure with vac hose removed on FSE fuel gauge, running 16 PSi boost ) ?Ideas welcome!

Thanks

Neil