2011 f150 5.0. I changed the factory plugs at 50k and went back to motorcraft CYFS12Y plugs. At 56k the short block was changed under warranty for a defective cylinder, which caused a knock. The original heads were kept. Also at 57k I had to flush the coolant and had fresh Ford coolant added back because I had to replace several coolant hoses. Now for today. I have 103k now and my truck always runs rich a startup, then clears up. It also has a slight rough idle and the check engine light flashes under hard acceleration. The CEL goes off and only the random misfire code is stored. So I figured I'd put in these new MSD plugs, part # 3743. They are pre gapped. Now my concern is that the plug on the front driver side had oil on the threads and there was a small pool (very small) of oil in the tube. I cleaned out the tube before I put in the new plugs. On the passenger side the plug second from the front had fuel on the tip and seemed wet (compared to the others. ) Half of the plugs had a fair amount of rust on the threads and where the threads meet the seat. I made sure to use a small amount of copper anti seize on the new plug threads to stop the rust. I've included pictures. What really bothers me is the oil on the first plug and in the tube. Anybody who wants to chime in would be appreciated.

 

Replace the cam cover O-rings or valve cover gaskets as some may call them. The plug well tubes are sealed by those O-rings. Most after market suppliers have complete kits which is the valve cover and plug well tube seals Ford part #6C535B.


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Ah thank you. Doesn't look that bad to change. How about the rust? I just took my truck on the road. At hard acceleration the CEL blinked as usual, but now it stayed on. It must have misfired hard enough to trigger it.

 

Rust is normal, the plug bottom/threads is steel afterall.
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thank you sir!

 

My plugs were especially rusty and brown after I used some crappy gas and crappy octane booster.

Throwing that in there in case it might be relevant to you!