This seems like a myth / old wives' tale to me, an internal engine overheat will change external / head temps by ~20 degrees most likely (by the time you shut her down) take into account the limited contact area of a coil-on-plug (plastic tube, metal spring) and the coil probably sees little or no temp difference during an overheat.

I've worked on a ton of cars and NEVER seen multiple coil failures at once which ended up being the coils. I've seen signs that point that direction but it's always bad plugs, bad ground, or a poor contact area of the spring/extension tubes which shorts to the head or surrounding wires, etc.

Regardless, once you swap coils, if it's the coil you'll always see the misfire follow that coil wherever you put it (even if you have multiple misfires) - just move it to a good one and you'll know right away.

FWIW I don't really recall seeing many coil issues with the 4.4 AJ-V8 ignition setup, if ever.

 

Coils fail on the 4.4 quite regularly. In fact most I've seen have had a combination of ND and FoMoCo coils because at least one or two had already failed in its life.

But you are correct in that my trouble shooting process was moving the coils to see if the misfire moved with them.

 

That's crazy, I've had two ~100k 4.4 AJ-V8 vehicles with zero misfire/coil issues and my indy shop hasn't seen many either, how many miles are on yours - it's the 06??

 

I'm not new Land Rover material, so I buy them cheap with lots of miles. I had 160,000ish on the first one (and about 200,000 when I sold it) and I think my current one has 150,000 but it's got a recent 90,000ish mile used engine.

Maybe they just take more time to fail. They're are some of the most reliable Land Rovers around in my opinion. I will say be careful with after mart coils. I replaced all of the coils on the first one and two of the new coils were bad in the first couple of months. It could have been a manufacturing defect I guess, and RockAuto replaced them no questions asked, and they've been fine since (I sold the car to a friend), but I think in the future I'll at least consider OE parts either from Ford or Land Rover.

 

A late update

Cleaned throttle body a few weeks ago, but been away with work.

Unfortunately the clean had no effect, and also informed by a bodyshop I had some work done in 'You know it's only running on 7 cylinders?' All voltages seem fine from a brief look.

Search continues.

 

A little bit off topic, but I just had a coil failure the other day. I had to replace a coil previously due to a torn boot when removing the coil pack (it stuck in the cylinder), but this was the first that failed while driving and threw the check engine light.

I also noticed that the new coils are FoMoCo coils and was wondering if there is any part number cross reference to a Ford part? I almost **** a brick when I had to pay $101 at the dealership for a new coil. Normally, I would have ordered an OEM coil off the internet (or perhaps aftermarket), but I was running on 7 cylinders and didn't want to keep dumping fuel into a non-firing cylinder and fouling my O2 sensors and cats. :P If anybody happens to know of a Ford part that is the same coil, but cheaper, I'd love to hear it!

 

FWIW Delphi coils show a list price of about $65 and NAPA at $63 - they're both very good in my experience (and obviously Delphi is OE as well..)

Definitely no reason to pay anywhere near $100.

Having said that, I've gotten coils for 5.4 fords as cheap as $22 before (shop cost but still, retail wouldn't have been more than $40 probably.)

Usually if there's a compatible part it'll automatically display it though - if guess the depth on the head would vary widely by application, even if Ford was around when the vehicle was developed.

I can give you the Delphi numbers if you're interested though.

 

Thanks! I found the part number on the RockAuto website... and it was only about $40. I think I may just order one and keep it as a spare so I'm not gouged next time I need one quickly!

 

I'm a parts manager at a Ford dealer, gimme some numbers off the coil and I'll what I can find for you.

 

Hey Dusty,

Sorry that I didn't see your post earlier... I think I just missed it. Anyway, I actually did take a picture of the coil pack before I installed it. I'll try to upload the photo from my phone here and see if it works. Thanks!