2017 Limited P0306 cylinder 6 misfire - again

[Geargambler]

I'm about to embark on yet another troubleshooting episode for the cylinder 6 misfire. I have a 2017 Expedition limited. First time this happened was back in November 2023. I bought an NGK coil and amazon delivered it next day. I swapped the coil and it ran perfectly... for 5 months. Then the code popped up again with the same symptoms, CEL, running rough, missing, limp mode. I bought another NGK, removed the 'old' NGK and again it ran perectly. So good that I took my family while pulling an enclosed car trailer with my cobra in it to carlisle ford nationals and back. No issues at all. I went as far as buying a set of 6 coils from a vendor on ebay that are OEM replacement motorcraft. I did a remove and replace with the motorcraft and immediately it threw a code and ran like crap. I put the NGK back in and it was fine. I returned the motorcraft set. Twenty days later, the misfire is back again. Same cylinder 6.

First thing I'm going to do is pull the coil and plug to see if the plug is fouled. If not, I'm going to swap the coil from 6 to 4 and see if 4 misfires. When I do this I'm gong to pull the negative battery lead to reset. I have a code puller, but I want the ECU to re-learn.

Possible causes from reading and searching: bad coil, again. injector clogged. faulty or broken wire. ECU issue.

Follow along as I find the root cause for this nonsense.

Few questions!
What aftermarket coils is everyone running? Part numbers?
I replaced the plugs not too long ago with OEM motorcraft. Read some threads about NGK plugs one heat range colder. They worth it? Part number?

 

[Geargambler]

Update June 26 2024

pulled the coil and plug, both looked good. disconnected the negative battery cable. reinstalled the plug and coil and the negative battery cable. took it for a ride and same running rough, check engine light. Code reader said cylinder 6 misfire. clear codes.

 

[Geargambler]

Next iteration

disconnect negative battery cable. remove cylinder 6 NGK coil. remove cylinder 5 OEM coil. swap the two so NGK is in cylinder 5. reconnect battery cable. take it for a ride and feels different, but still missing and check engine light comes on. read codes and now have a cylinder 5 misfire. clear codes and park it for the night.

clearly this is another bad coil. what is everyone using for coils that last? this is my second NGK and the OEM ones didnt work out of the box. any help would be great!

 

[Cluster333]

You didn't mention the gap on the plugs maybe the NGK coil is sensitive to the bigger gap on the plugs.
I was getting random phantom flashing check engine light but no codes stored. I changed all spark plugs and used stock Motorcraft. Resolved my issue. Then about 30,000 miles later misfires came back. The gap was way off so I changed all coils with Motorcraft and bought the gt cooler spark plugs gapped at .028.

2010-2020 2.7L/3.5L EcoBoost Ford Performance “GT” Cold Spark Plugs M-12405-35T​

 

[Geargambler]

I ordered the plugs. Picked up a brand new coil from Ford, which was of course expensive. Replaced the cylinder 5 NGK coil and truck runs just fine now. I'll change the plugs this week and report back again.

 

[jdevine]

Similar situation. Bought a 2017 expedition Platinum February. Not knowing its history I changed the plugs and coils with what were sold as genuine Motorcraft parts on Ebay. Started throwing codes on all cylinders. Put the old coils back in ran fine. I think that the reason the Ebay parts were so reasonable is that they were knockoff. Went out and bought the real things from another source and everything worked fine. I might also mention that you have to be very careful re-gaping the iridium plugs to .028 that you do not mess up the center electrode, it is really easy to do.

 

[Geargambler]

Update.

I installed the coil from the dealership, disconnected battery, reconnected and took it for a ride. It ran perfectly.

Next day I changed the plugs to the above mentioned ford racing plugs, disconnected battery, reconnected and took it for a ride. Definitely a noticeable difference! It's absolutely more 'snappy' now. I'm definitely pleased with how its performing now.

I guess those coils I got from eBay, although they looked authentic, were likely counterfeit.

Hopefully this thread is helpful to others!