On the off chance anyone is curious my V6 is still running quite well, nearing 350K miles.

This issue concerns my V8. I had an issue crop up suddenly regarding an extremely rough idle and misfires. On all 8 cylinders. Expecting this to be a standard, clear cut issue, I replaced the spark plugs, cleaned the injectors, dropped the fuel tank, inspected the filter, tested fuel pressures, cleaned the MAF, cleaned the throttle body, cleaned the EGR, cleaned every electrical connector I could find, inspected the wire harness, the intake, ensured all fluids were correct, inspected several sensors/cleaned them.... inspected and cleaned ground connections... and more

I have always run the vehicle with premium. Raising the octane further has no effect, although strangely, when driven for some time at speed, the misfires disappear. The colder it is the worse it is. Several times when cold I have had issues with stalling/failure to start.

The only codes I have are as follows
Misfire cyl 1-8 (independent code for every cylinder)
Random misfire
Misfire on low fuel

Code wise, I have nothing else to work with and I am out of ideas. I don't pretend to be an LR tech or a pro tier mechanic, it is possible I have been a total idiot in my troubleshooting. Any ideas, any thoughts, anything I am going to be grateful for. I have the IID, surely there is some way to diagnose this using the tool that I am not aware of or capable of figuring out. I have spoken to several mechanics in the area who are booked for weeks, and who have not given me any help advice wise.

Thanks

 

What about the coils? Most misfire issues I've read about on LR3 forums for the past 16 years have been related to coils. With you having misfires on all cylinders, then maybe it's whatever component is controlling the coils. I don't remember what that's called but the 4.4 must have one. My old Montero did and that was the problem when I had misfire issues....it was the little "coil brain." Cheap and easy fix.

 

The ECM controls the coils directly. If there were an ECM issue, you should be logging an ECM specific fault.

The only shared component of all coils/plugs beyond the ECM is a capacitor that is wired in parallel to prevent radio frequency interference. Perhaps that failing would cause misfires.



First thing to come to my mind when reading your symptoms was throttle body. Rough idle, but runs ok under load. Usually cleaning fixes it, which you’ve done. There should be a way to watch throttle body position live data along side misfire counters for various cylinders, that might give you more insight.

 

I think I read that if the RF Capacitor fails you can get a no-start issue. On the other hand, you can disconnect it and things will be fine; it's not needed.

 

As I understand it the LR3 has no distributor, the controller is the ECU. There is a grim possibility that that is the issue.

Nonetheless, coil replacement was todays project. I began with two coils, replacing cylinder five and seven. The result was misfires on only two cylinders, three and eight I believe. While I can not begin to understand the cause of that, I thought I was on the right track so I sourced 8 new coil packs, in addition to the two I could find this morning.

After installing all 8, the result was global misfire except for cylinder six. Again, I have absolutely no idea why that would be the case.

I'd deeply appreciate any suggestions

Edit: For some reason the site did not update the thread until I posted, I will record the live data Seattle suggested, and mess with the RF Capacitor. Once the beer kicks in. This process is extremely frustrating.
.

 

Just fyi, the rf capacitor can be bypassed, but not disconnected.

 

I have been rotating the coils, at one point I got it to misfire only on 1, 3, and 7. Then I screwed with those for a bit and the result was a return to misfire on all cylinders but #6. Figured I'd remove the sparkplugs on 1, 3, and 7, just to see. Quite a bit of oil on the threads/plug.

No coolant in the oil. Oil on the plugs. Any more suggestions? From a brief read this can be something caused by or a result of misfire, so it may be no clue at all, only a symptom.

 

Sounds like you could do with replacing all the coils. I've had good luck with Delphi and NGK ones. You can get them from Rockauto fairly reasonably.

 

...These are coils I purchased this week. These are plugs I installed 6mo ago. I have attempted the rotation procedure with the old coils/plugs as well. Best I can get is 5 working cylinders. Every coil is brand new. Every plug is brand new. I am rotating brand new coils and getting different results. I have oil on my plugs. Both the thread end and the spark end.

At this point, between dropping my tools in the engine bay, I am attempting to remove the valve covers so I can get an idea of what is going on. Any maintenance guide or video would be appreciated, some of the bolts are in difficult to reach places.

Additionally I sort of need to know what I should expect to see vs what I have

Also, as for the live data, I found I was getting a misfires on cylinder 1 at a ratio of 4:1 vs all other cylinders, indicating to me that there may be a significant problem there, somewhere. But could that cause cascade failure in the rest of them? No idea.

 

Misfires in one cylinder can show up / be incorrectly detected in adjacent or opposite cylinders....If your plugs are fouled by oil now, you might want to try a new set.
Have you done head gasket or compression tests? Regardless you will need to fix the oil issue - typically that comes from leaking spark plug tube seals in the valve cover, but I don't have personal experience with how those are laid out in the 4.4.
Here's a link to the seals with the valve cover gaskets:
https://www.rockauto.com/en/catalog/...r+gasket,10710