So, a mechanic was working on a friends car and put a screw drive on the injector (of her 300sdl) and put the plastic end up to his ear.

She tells me that he was able to diagnose 3 "bad" injectors this way. My question is what was he hearing and does this trick actually work.

I would love to do this with my 300d to check and see if I should replace the injectors (without going to the trouble of popping them out and pop testing them).

Any thoughts on what to listen for?

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Thanks,
Will

1985 300D- 222k- (bad transmission)
1980 300D- (parts car)
1982 300SD- 242k