Possible Causes
WARNING: This page is about a different car, the 2002 Mazda B4000, 2002 Mazda B3000, and 2002 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.
Fuel injectors are electrically operated solenoids. Injectors open and close a constant number of times per crankshaft revolution. Amount of fuel is controlled by adjusting injector pulse width. Injectors are normally closed and opened by 12-volt VPWR from PCM power relay. PCM controls PCM power relay ground. Possible cause is faulty fuel injector driver inside PCM.