I just replaced the oxygen sensors started the car up and it was sitting there ideling and it died .we tryed hooking a scanner up to the access port amd it has no power at all..the engine cranks over .and all lights windows stero every thing works .it just wont fire up. I had a spare ecu in the garage so i even gace it a try and still didnt fire up...what could cause this? All fuses ,grounds and all have been checked a ny input is appreciated thanx......the car is a 20022 subaru wrx 2.0 has aem intake and magan header n full exhaust thats only mods basicaly stock