my 1998 ,120 excavator , will run fine as can be but when I move my joy sticks to dig or pick up heavy things it overload the engine and smoke black smoke and go dead !!!! I have changed fuel, oil , hyd & air filter, serviced them all up , check all fuel line connections for any leaks or drawing in air, was wondering if it could be in fuel pump, or needs new injectors ?? Need to get up and running bad ????