there is tool you can purchase on ebay. it is a box that pulses each injector a specific amount of times. you use this box with a fuel pressure gauge. you hook the box up to each injector and to the fuel pump. press the button and the box pulses the injectors ~6 times and you should see the pressure drop on the fuel gauge. each injector should have the same pressure drop. the injector/s with the least amount of pressure drop or no pressure drop at all are the bad ones.