2004-2005 Kawasaki STX-15F Jet Ski Factory Service Manual., Page 98Get this manual
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3-50 FUEL SYSTEM (DFI) Fuel Injectors (Service CodeCharacter-41, 42, 43, 44 InJ1, InJ2, InJ3, InJ4)
If the power source voltage is less than standard, check the wiring (see Wiring Diagram