This cylinder just started throwing misfire codes this week (one misfire every 50 miles or so). I've been all through the ignition system from my last misfire journey.

I don't see coolant, do you?

Injector maybe? Is there an easy way to test?

Thanks

~MAx

 

HOLY **** BATMAN!!! THATS A HUGE PICTURE!!! I DIDNT EVEN NEED MY GLASS'SSES'SSSES'.

Its got some carbon on it.

 

I don't see coolant but it is very sooty. I would check the wire very closely and replace the plug to eliminate that possibility. If it was the injector leaking it would smell like fuel. If it was the injector not opening there would be no soot. Since it is intermittant it is not a compression problem or sticking valve. Good luck.

 

How does it look?

It looks friggin' huge man!

But seriously, they look like the ones I replaced a few months ago, no codes.

 

Wow...poster-sized picture!
They look like my old spark plugs that had 100k on them.

 

Those plugs only have about 1,000 miles on them. Just checked another one... It still has soot on it, but not as much. What makes the soot, and what could make more of it on one cylinder?

~Max

 

The soot is caused by incomplete combustion. Often because the mixture is rich, or because of a misfire. It could also be from oil in the cylinder but that would appear wet and "oily".

 

First try scaling down your picture to 1080x764

Look at or feel the bottom of your valve covers. There may be oil dripping on the socket connectors of your O2 sensors. The O2 sensors are in front of your Cats. This can foul the O2 sensors and make your truck run rich. You could buying one new front O2 sensor and see if it solves your problem. I think at some point every Discovery owner has this misfire problem. Many times it is confused as bad plugs or wires or a bad ignition coil. The ignition coils or injectors rarely go bad. Most of the time its the O2 sensors. Also try running 2/3 bottles of Chevron Techron injector cleaner with about a 1/4 tank of gas. That will super clean your injectors. All these suggestions are the cheap route to self diagnosis this problem. Try Magecore or STI 8mm plug wires if you have over 60k on your current wires. Get back with us on your results.