Recently, I have noticed that my 1994 Mercedes E320 Sedan is idling and running very rough. It appeared to be missing. Upon further investigation I found out that Cylinder 1 & 6 were not firing at all. I thought that the coil on sparkplug 6 has turned bad, so I switched the coil 3 with coil 1 on sparkplug 2 which was working fine. After the switch I noticed the coil 3 in fact is fine but the replaced coil on sparkplug 6, which was working previously on sparkplug 2, is not working and spark plug on cylinder 1 and 6 are still not firing. I am stuck now. Could you please help me with the diagnoses from this point on so that I can detect the problem and replace the bad part/parts, if any, and be able to run this vehicle? How do I perform the tests to nail down the problem? If you have a wiring diagram for ignition, that would be a big help? Your assistance in this matter will be appreciated.