Ok. Does the tach needle bounce or jiggle at all when you're cranking the engine?

Can you pull the distributor cap, rotor, and fiber(?) cover plate off? Then you can take the lead from coil to cap off the cap and attach to a spare spark plug.
There is a sensor called the Hall sensor. The attachment point is weak, and the wiring can wear out if the plastic attachment is broken.

If you check through my threads, I started one like "!@#%^%& no start". There is a procedure there for testing the spark system and narrowing down the possible problems. There are also wiring diagrams for I think 85.


This is the hall sensor.

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1990 740 Turbo, on its way to stock specs, maybe beyond