It's good that you confirmed it was the #6 wire. How did you determine that? Did you see arcing? Did you swap wires? Knowing how you confirmed it may help others.

 

No I didn't see any arcing. What I did was clear the codes, and then start the engine to see what came back. P0306 popped first, then P0301 and P0300. Then I'd get the P1300 O2 sensor alert. I tried this a couple of times so I was suspecting cylinder 6 plug or wire was the issue based on the order the codes appeared. I was really hoping the coil was fine.

I changed the spark plug first since cylinder 6 is easy to reach. The new plug didn't help, after the change the same codes appeared in the same order. So I read the thread on changing ignition wires without removing the header, and swapped the cylinder 6 wire with a known good one. Put the parts back on, and fired the engine up. No error codes, so I took the Disco out for a drive. So far everything is running smooth.

The plan is to swap out all the plugs and wires for some preventative maintenance

 

Excellent diagnostic work.

I don't know how others change the wires but when I did it I laid face-down on top of the engine using a foam camping sleeping pad and did it without removing the upper intake. (This is one case where it helps to have girlie-man hands.) But while moving around in that position I managed to break both the brake servo vacuum line and the PCV line fitting where they enter the upper intake on the right-hand side of the engine, so if you choose to change the wires without removing the intake be sure to disconnect these two lines so you don't break them like I did. (To remove the brake servo line push IN on the red ring while pulling the line OUT.)

Good luck! And let us know how it goes.

 

Now that I've done several spark plug wire & recently replaced the coil pack on my Kalahari it's just an extra 12 bolts. It makes it so much easier IMHO when doing all 8 spark plug wires or replacing the coil packs (especially if you have SAI).

Also if you're tired of your throttle body heater plate leaking if you're removing the intake manifold that is the perfect time to bypass that sucker properly and feed the intake line back to the coolant reservoir. I use 5/16 heater hose and then use a Kingsborne Spark Plug Wire Protector Boot over the hose.

I just did it on my friends 03 (without SAI) and it went really fast. I even took my time and really got the spark plug wires routed perfectly. Start to finish including changing the spark plugs was 2hr.

Glad yours was just a spark plug wire. On my Kalahari I thought for sure it was the Bosch 2x Plug someone had slapped in there, then I thought it was the wire, and nope it ended up being the coil pack, but 229K out of the original coil packs = not gonna complain one bit.