I have a 78 450sl and I did a spark plug, plug wire, cap and rotor change . They all looked good except the one closest to the firewall on the passenger side. The plug had a little oil on it and I could see a small amount of oil in the cylinder. It has 223,000 miles on it and has been running great but lately it seems hard to start and runs rough when cold. I know it could be the rings or may be the valve guides. I need to do a compression check but how do I tell where the oil is coming from ? Any ideas would be appreciated. Thanks

 

Thanks for the info. I did a compression check and it's 150 pounds. could the fuel injector not be working and burning off the oil ? It has been like this for quite a while and every time it starts running bad after a few thousand miles I replace the cap & rotor and it solves it. But this time it didn't, That is why I replaced the plugs and wires also. There is no smoke and it doesn't use hardly any oil .

 

I just replaced the injector and it runs like a champ. I think I will look at cleaning the remaining injectors because this one was so dirty it wouldn't come clean and I want to catch the rest before they get too dirty.