My 94 E320 failed smog so I replaced the plugs. It ran just fine. Took it to the smog check place and apparently the wire to the coil sagged and internally shorted so it was now a "Gross Polluter". I checked the 12V to the coils and the insulation on the wiring had turned to dust, letting the wires short out. Since a new set of wires would cost over $1300, I junked the car.
I think it is absolutely inexcusable for MBZ to not get their wire supplier to pay for replacing the defective product as wiring should last the life of the car.

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'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles