mpg cut in half 4G15 HELP

okay right when i got my 2001 mitsubishit mirage 1.5 it was getting about 41 mpg. then i stuck a cold air intake, universal exhaust, spark plug wires (ACCEL), and Bosch 4 spark plugs. and it seems to run lean spark plugs have a white coating and my gas mileage is about 20 have no idea can anyone help PLEASE

when ur car gets better performance ur gas milage will drop, but urs seems to have droped too much, i dont know what that could be.

Check your o2 sensors. If you have a bad o2 it could be causing the ecu to think that the car is running lean, and continue to dump in more and more fuel to compensate for it.

did u reset your ecu