Ryan, shortly after I bought our 1991 300CE in 2000 I asked an experienced tech at our local MB dealer what spark plug he recommended for that car. He said that from their Service Department's experience the 104 engines perform best with Bosch F8DC4 spark plugs. So I use them exclusively in our 1991 300CE, 1992 300CE and 1995 E320. All run superbly and I change spark plugs every 30,000 miles. Be sure to gap per the Owner's Manual specification.

Inpsect the condition of the distributor cap and rotor when you change spark plugs. Clean terminals, or replace as required ... likely every 60,000 miles. Recommend carefully inspecting the ignition wires since they can cause running issues also.

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Fred Hoelzle