For a quick and simple test, I’ve used a mechanics stethoscope to listen for a “clicking” noise coming from the fuel injector by placing the tip of the stethoscope on the injector. Compare the sound of #8 to the other injectors that are performing. I’m sure if you’ve done any searches you have seen numerous references to the engine wiring harness. What’s know as the main engine wiring harness, houses the wiring for the fuel injectors. If the wiring connecting to your problem injector is faulty, it might be the source of your problem.

Of course you probable want to perform a injector leakage test and a spray pattern test.

__________________
Russell McMahon
Tulsa, OK
2001 CLK 320
1992 400se
1993 400e
2000 320ML