Can bad Fuel Pressure regulator reduce mileage ?
OK..I have worked on many different type engines in my life, Aircraft,Motorcycle, Automobile, Diesel, and Now have a problem with excessive fuel usage in my small car,in cold weather, I know winter time will cause every vehicle to lose 2 maybe 3 miles
You mentioned some maintenance, doing all maintenance may help. I dunno if your car has an in-line fuel filter. Check the fuel pump's flow & psi. You can check it anywhere, just disconnect before the fuel rail or any place that's ez to reach.
We sure all just take our car and 
My pressure regulator for my 1984 528e started leaking over my engine and the BMW part no longer existed. We picked up the correct part, but my local mechanic, after checking, said the pressure regulator was not needed and he straightlined the fuel line to the pump. The car runs hard and choppy sometimes. Is a pressure regulator needed?
Fuel Pressure Regulators for Your Engine
As we keep saying, one of the ways that automakers will meet more stringent fuel economy regulations is by making smaller engines that work harder. Now Fiat has one-upped its European competition by announcing it will offer a 900cc turbocharged twin in European models of its Fiat 500 mini-car.