3.9L Lincoln LS Miss ... HELP
 

I need help diagnosing a single cylinder miss. Coil pack, spark plug, and fuel injector have all been swapped around, but miss persists on same cylinder.

At this point, I'm suspecting that an exhaust valve may be stuck partially open causing the miss fire. One thing that got me to thinking about this is that on the side that the miss is on, the exhaust pipe is actually sucking air in, while the other side is blowing exhaust out.

I'm thinking about opening it up to investigate this theory more over the weekend, but want to get some feedback first.

Or perhaps it's a burnt valve.

Wouldn't even know where to begin. Drain a quart of oil out and swap in a quart of "Marvel Mystery Oil" would be my first recommendation... would relieve a stuck valve or just about anything else "stuck" in there. :shrug:

Perform a compression test or a cylinder leak down test.

check the spark plug boot for a crack. The boots and valve covers are notorious to leak oil onto the spark plugs. The LS i had was nothing but a big headache. Lots of stuff broke before 100,000 miles.

That was corrected about a year ago. Replaced a bad coilpack and changed the other boots. Installed new valve cover gaskets to fix the oil leak issue.