Can get one at Autozone and hold the stethoscope to the injector you should the woosh sound of gas going through the injector but also a very audible kinda clicking sound. Sounds like tat tat tat tat. Can use a noid light on the harness to check for a grounded harness holding the injector open. The noid lights are a loan a tool at Autozone as well.
The plug would either be really bright white or really black and wet with gas.
White is stuck closed and black stuck open.
You can also put a fuel pressure tester on the schrader valve on the fuel rail, turn the key on to where all the indicator lamps turn on, let the fuel pump get through its prime cycle and clamp both the feed and return fuel lines shut with hose pliers or vise grips. May want to use a rag or something to not chew the hoses up. Once you have the lines closed off monitor the fuel pressure gauge. Shouldn't move much, but if it does you definitely have a leaky injector of a leak in the metal line going to or coming from the rail.
Can't think of any other way besides having the injector off and having it tested.
Good luck,
Jerry Berger
