I was wrong in my last post that the ignition and fuel computer worked together. In a 86 420 the Ignition and fuel computer are separate items and each does it's job without the help of the other. I am still right that the MSD system wouldn't work on the 420 because of the advance curves etc are calculated in the ignition control unit and the MSD is not set up for that. Diagnosing is about the same as the 85 and earlier except the pickup coil is at the flywheel instead of the distributor.

Sorry for the bad information.

Paul

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84 500 SEL (307,xxx miles)