ragobro, please provide some more information about the no start problem. What are the circumstances surrounding the problem, including the mileage on your 1991 300SE? Engine running rough, then no start ... engine running fine, then suddenly no start. If your 1991 300SE was running fine then suddenly wouldn't start I would suspect the ignition control unit (ICU) mounted in the driver's side inner fender. Either swap yours in a similar car that runs and see if that produces a no start situation, or swap a known good ignition control unit into your 1991 300SE.

Failure to maintain ignition system components (spark plugs, distributor cap, distributor rotor, ignition wires, coil) can cause the ICU to fail so I recommend installing the ICU from your 1991 300SE into a running car to check if yours is bad. The good news is you should be able to purchase a reconditioned ICU from your local MB dealer.

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Fred Hoelzle