My 2003 mustang GT with a 4.6 engine sat for 2 month with the key on accessories. The battery was dead, I charged the battery and the engine would turn over but not fire up. I sprayed starting fluid in the air cleaner and the car will run until i quite spraying. I then discovered the fuel pump was not running. Ive got 12 volts to the pump so i installed a new pump. The car still will not start. A Snap-on scanner says fuel pump or fuel pump control module. What do ya'll think? thanks. Why would leaving the key on accesories cause this problem? thanks again !
What makes this problem better or worse?
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Since it’s quite possible you mistakenly tested the wrong fuel pump circuit - check the Fuel Pump Cut Off Switch in the trunk - also called inertia switch.
(Fuel gauge sender also has 12 volts applied)
Car may have been jostled a bit while parked - it doesn’t take much to trip that switch to the OFF position. Good luck!