If the coil is good, the only other thing that will cause low spark voltage that I know of is a bad switching unit. I believe in the 190 this is also an EZL unit, although there may be a distributor rather than just the rotor on the end of the cam.

If the current going to the coil is inadequate, the spark developed with the current shuts off will be weak.

Check for corrosion in the connectors for the coil on both ends (at the coil and at the switchbox unit).

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!