PeachParts Mercedes-Benz Forum - View Single Post - OM 603.961/71 Rebuilt Upper End Lumpy Cold Start

Diseasel300 · #2 11-26-2018, 07:10 PM

The .97's used an afterglow relay and use a different glow plug from the .96x engines. If you're using your original W124 relay, it doesn't have afterglow and you can expect an occasional chug or clatter in the first 30-60 seconds of operation when cold.

Excessive missing out or chugging can indicate air in the fuel system. Check your rubber hoses and banjo bolts for wetness and/or sweating. If it's still in the circuit, be aware that the fuel heater thermostat is an extremely common source of air ingress since it's on the suction side of the lift pump and has an O-ring seal that perishes with age.