I would guess it's an 81-83 engine. The pickup is at the front of the engine. What's odd is the tach works smoothly, very fluid. But, it's the speed that's registering too fast. Now, someone mentioned an adjustment screw on the tach circuit board. Is this the case on an 85 W123? I'd love to address it from that angle if it's that simple. I can get it close by ear. Well, closer.

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1987 300SDL #1, 1987 300SDL #2, 1980 240D, 1982 300SD, 1994 S350, 1990 350SDL, 1991 350SD, 1985 300D, 2005 E320CDI

Gone, but not forgotten: 1981 300SD, 1982 300SD, 1987 300SDL, 1983 300TD, 1980 300CD, 1981 300SD #2, 1987 300D, 1987 300TDT, 1980 300D