Hi all
I have been looking through the forums before posting.

I have a 2003 Discovery II. I have been getting a check engine flashing with the error code for misfire Cyl4.

It happens only after the truck sits overnight or several hours.
The plug wire was severely burned so I replaced them all and plugs.

Still does it, when I pull the plug out its "wet" with what looks like PCV smelling oil. Its not losing coollant, but I have had to replace the top hose and the coollant return pipe as they started leaking recently.

Oil is clean, coolant looks ok but does have that PCV smell a bit but no oil.

I am suspecting a head gasket issue, but its not real clear, maybe a valve seal? reading other threads it was mentioned that there is no water channel near the number 4. No other cyls are affected, runs great after the inital missfire.

It seems to be getting worse and does it more, start engine and cyl 4 misfiring then clears up.

Thanks for the consideration.

 

If the plug is oily that would make me think rings or something. Perhaps the oily stuff is unburned fuel and carbon? Maybe that burned wire damaged the coil that powers number 4? Just guesses. I'd do a compression test if it's oil and check for spark on that cylinder if it's fuel.

An injector that is sticking open a little and leaking would have similar symptoms. Fills the chamber with fuel when you shut off the engine, and it takes a few minutes to burn off when it starts again, then runs fine.

 

weird. theres no real way for oil to get in there overnight, unless you filled the engine up to the valve covers with oil =] (dont laugh, its happened). Is it gas? if the injector is clogged it could be bleeding into the cyl, that would make it miss a few times. (unlikely) Do this, Hook a scanner up to it, go to live data, watch the short term fuel trims. when the management switches to closed loop, see if one of the trims starts climbing until the motor starts missing.
I just had a 03 disco come to my shop with a cyl 8 missfire. ran awesome except wen first started. as soon as the oxygen sensors warmed up the right bank trims would go 2% - 3% - 4% (engine would start to miss slightly) 5% 6% 7% (engine would run BAD) set missfire code, (only cyl 8) go open loop (factory program) then run PERFECT. Turned out to have just a bit of cheese and some dirty plugs in the oxygen sensor plug. this caused the computer to think the bank was running lean and added fuel untill the engine started missing.

 

Thanks for the reply's The O2 issue could be a consideration, what you described is what exactly it does, and its not really getting worse, I will investigate the sensors, I dont have access to a diag tool, just got an ODB2 reader

 

How did the plug wire get "severely burned"? When you installed new ignition leads I assume you installed new plugs as well?

My point is that ignition wires don't just burn up for no good reason. If you don't know why it got severely burned you need to find out. Maybe a bad plug or coil pack, seems like possibly that lead was getting shorted to ground which could cause it to burn up like that.