Climbing down the wormhole but thought I'd post to see if there might be something I haven't thought of. 1995 E420, 171,000 miles, out for a drive for approx. 15 minutes when the car suddenly felt like it was running on 4 or 6 cylinders. Felt similar to a caps failure but they're 3 mo. old so I ruled them out. Limped the car home and replaced all the plugs. Same issue. (no CEL) ran the codes anyway and the DM showed an ignition failure on bank 1 so I went down the train and replaced the Ignition coils. Same problem. Next down the line, replaced the EZL. Again, same issue. This time though the car threw a CEL and SRS light. Tried running the codes through Xentry and showed the DM as clear of faults. Also, the onboard diagnostic module holds the red LED when pressed and nothing after. Replaced the fuel filter and confirmed fuel pumps are good. Pressure regulator was replaced last year so that's good.

Live data shows proper voltage to MAF, O2 and ignition is stable at 30v / cylinder so it's not an ignition issue as far as I can tell. Based on the fact that the DM is unresponsive am thinking there's a wiring issue but the main harness has already been replaced with updated wiring and looks good. Lower harness is original but don't know if that might be the culprit considering it isn't controlling much outside of the the starter and alternator.

Car smells running rich but no rotten egg smell so I don't think the cats are bad.

Pretty much stuck at this point so if anyone has any insights let me know.

Thanks in advance!

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1995 E420
1998 SL500 Sport
2009 E350 Sport
1995 S500 Coupe
1992 500 SEL