1973 450SL, (Previous 2008 ML350,2002 E320 Wagon, 2000 SLK230)
I just want to thank you for this suggestion. My '73 450SL has been missing/loping/running rich since I bought it. I was at my wits end, even looking at potential replacing the distributor or trigger points when I came across this. I pulled one of the plugs that an indie installed (plugs, points, wires, cap, rotor, etc - $1000 and still had the lope). They installed Bosh R6 plugs. I replaced them with what was immediately available - NGK BPR5EGP, and after the smoke and colorful language cleared I turned the key. No stuttering, no loping, no drop in idle. It followed from cold to hot and ran perfectly - the best this has ever run. I took it for a ride and it was a pleasure, without having to pull off the gas, overexert the pedal - just drive. I'm hoping this is definitely the fix, but doing so absolutely improved the performance. Thank you!!Hi Hans,
try to change the electrical connectors between cylinder 5 injector and cylinder 6 injector.
The time the injectors 'fire' doesn't matter much, and you can check if the error moves to cylinder 6.
Try to interchange the spark plugs between the cylinders, too. A good spark in free air doesn't mean they function properly in the engine under pressure.
The spark plugs mounted are 'suboptimal'. The 'R' means 'resistor' and originally no resistor plugs were used. Resistor plugs tend to get bad.
Using resistor plugs is not a problem on most engines, but the M116 is quite sensitive.
Buy the Bosch spark-plugs directly from Mercedes <not the maybe fake aftermarket scrap> or try NGK BP6ES.