Mine was sitting on the red hot SAI pipe, that should have that white mesh stuff on it. Burned through the insulation. I think any other metal bit wouldn't get hot enough, unless there was a wire fault.

My wire popped out of the little black holder clips and went rogue.

If Abran has seen 2 blocks crack and be evident on #5, that has to be a suspicion.

Good luck.

 

You would be looking for an actual misfire field on the scanner. It would show a misfire count every time that cylinder misfires.

 

Thanks! Just an update. Keeping an eye on things for now. Wife's been driving around town and no new CEL has come on. The alternator light has also began to flash intermittently the last 2 weeks also. Going to go over wires, vacuum hoses, alternator carefully this week. I want to chase down as much as I can and correct it.

 

there is one lone brown wire that runs off the back of the alternator, check that wire for chaffing

 

thanks for the alternator tip. that was next on my list:

Update: After a can of SeaFoam and some general wire jiggling, there have been no more check engine lights the the idling has smoothed out.

That said, I don't yet believe the problem is "solved" but it is much better. There is still a faint misfire that I can feel at idle. The alternator light is intermittently flashing for milliseconds at times.

One more thing I need to address is a couple months ago when my wife was laying atop the engine checking wires with her small hands, she snapped the plastic connectors off the two vacuum hoses in the top air intake.

I broke this: http://www.roverparts.com/Parts/LZN100220LG

And the larger plastic nipple to the left of it on the larger hose.

 

Just wanted to update again, for what it's worth.
About a week with no CEL on. I am 99% sure I found the culprit. When I replaced the wires a couple months back, my wife was leaning on the engine and snapped the plastic nipple for the vacuum line on top passenger side of the plenum beside the brake servo vacuum valve. I could not find a replacement at the time, so found a smaller one. I duct taped the threads to make it larger and shoved that in the hole. Apparently this caused a vacuum leak and was misfiring #5. When I got a new nipple and replaced the brake servo valve beside it (also had a taped tube shoved in that hole), the idle got much better, no more stumbling under power and no more lights.

That all said, the NGK Iridium plugs that were installed 6-8 months ago with the head gasket job likely fouled because of the leak, because there is now a very very minor misfire detected when I idle. I plan to replace all 8 plugs with Champion 7070's. #5 was pretty well fouled (carbon cake), so I am curious to see the other plugs. I replaced #5 already to be safe.

I'll post again after I replace the rest of the plugs. It seems that a vacuum leak was the likely culprit.

 

God bless you for wanting to got with the 7070s. They are, to me, the go-to choice for the "99-'02 trucks. No need for any of the other spark plug snake oil being peddled, in my opinion. But I see no reason to replace all the plugs unless there is some clear reason to do so.

It's not clear to me, however, just what part your wife broke (not to blame her; I know better than that). If it's the fitting connected to the short hose that runs to the top of the passenger-side valve cover a brass replacement is easily found in the plumbing department at your local hardware store, big box or otherwise.

That said, I doubt this item has caused the #5 misfire. But I also don't think its a coil problem. Coils rarely fail on these trucks. If you've swapped plugs I think it's most likely a problem with the plug wire, even if that's not what you'd like to hear.

 

Not my picture, got it online, but the hose to the left of the plenum, with the clamp, beside the red vacuum valve, if I pull that hose the engine chokes and dies. I am sure air was leaking in with the old brass connection that was too small. I got a new brass fitting and now it is noticeably smoother and stronger.

I agree it should not cause a single #5 misfire. I guessed it was causing multiple misfires. Will know soon when I pull plugs. When I put the new wires a while back I did put one wire in the wrong coil slot and pulling it out did involve really stretching the connector. Could have damaged one wire to 5. I tried swapping wires but it was connected so well I did not want to force it out and break anything

 

Update and Question:
So it's been about a week with no CEL light or codes. Engine is much better. Here is what I did that made much noticeable improvement:
1 - The two hoses connected to the passenger top side of the plenum were the big ones. When I got a proper fitting brass nipple and actually got a brake servo valve instead of shoving the tube in the hole with duct tape - no more stumbling, bumbling or codes, especially under load.
2- Cleaned air filter (K&N), cleaned MAF sensor, cleaned IAC valve.

3- replaced all plugs with Champion 7070

4- Plug closest to radiator on passenger side was only threaded 1/2 in. Cross threaded. Bought a back-tap tool and fixed that last night. Plug is now fully seated.

Here is where I am:
Cold Engine - no misfire or CEL light, but at idle, there is a very soft and minor "sputter". Not sure how to describe it. Kitten is purring perfectly softly, smoothly, the purr momentarily sputter-purrs and back to normal.

Warm Engine - purrs like a kitten at idle. Kitty purr is still slightly detectable, but better when warm. Great power under load. Sounds and runs strong - just that slight imperfect idle that I want to track down.

Idle is like:
PRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR-putump-PRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR-putump-PRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR

Any way to do some kind of voltage test to each individual plug wire to see if I can identify if it's momentary voltage change coming through the wire?

 

I'm wondering about these 7070s. I looked it up on Amazon, and it says it is double platinum spark plug, but that it does not fit the Disco. I looked up the double platinum on Champions website and it says Champion 7332. What am I missing? Heat range?