Have '03 Ram 1500 4.7 126K miles. Just replaced (4) O2 sensors all around and plugs. Everything was running fantastic. Then my truck sat for a long weekend and when I went to start up, the dreaded "clacking" sound from a misfiring cylinder came on real bad from the start. A bit of rough running and after it warmed up it settled down some but didn't go away.

Replaced plug, tried a new coil, checked voltage to coil (ok), and no elimination of noise. After a week or two the plug is fouled. Put some Marvel Mystery Oil in and it smoothed things a little. Got an oil change (thinking stuck lifter from sludge) and the cylinder misfire comes back. Have had the 300 code for #3 cylinder misfire. Code clears temporarily when I clean/replace plug but typically comes back and engine runs rough. Smells like raw fuel sometimes on start up.

Trying to think of the next step. I am going to add another pint of MMO to see if it smooths things out again but am worried it may be an injector issue. Anything else to try? Here is the plug after 2 weeks.

 

Plug color looks to the lean side. Do an injector leak down test. That will let you know if you have a bad injector. Try some sea foam in the tank first.

 

It's possible a rocker fell off. Pull valve cover to inspect.

 

 

Thanks for the replies. I'm an amateur mechanic compared to a lot of you guys so any experienced input is great.

I put some MMO in the oil last night (drained down some oil first) and it's running a little smoother today. I'm going to try some Sea Foam and then see about pulling the valve cover off if it's still missing.

 

The more you run it and pour crap in it, the more you're going to damage it. There is no such thing as magic in a can.

 

Looks like I had a slight head gasket leak that turned into a larger one. Taking it in tomorrow for repairs. Too big of a job for me.

 

I suppose that's better than dropping a valve.