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Old 10-02-2003, 01:50 AM
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sixto sixto is offline
smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 20,807
With an 85-up (84-up?) MB Diesel you can put a duty cycle meter or pulse counter on the crank sensor and calculate rpm. Or you can try something like a bicycle cadence meter with the sensor magnets mounted on one of the pulleys along the belt paths. You'll have to do some math and assume the belt isn't slipping but it'll be good enough I'm sure. There are aftermarket tachs for Ford and GM Diesels that attach to the alternator. I don't know how they work but I'll bet it can be adapted to an MB Diesel.

I've seen an IP timing device that reads the pulse through an injection line. That can be used as a tach signal.

95 S420
91 300SE
87 300SDL
83 300SD