My wife's 2012 EL King Ranch Expedition with 5.4 has 108,xxx miles on it and has been running rough and jerking at cruising speeds. I ran a live scan just now and it showed 6 of 8 cylinders with 1-5 misfires a piece. Only cylinders 1 and 8 show zero misfires. The plugs on the drivers side are Motorcraft and were replaced less than 20,000 miles ago. The plugs on the passenger side are NGK iridium and were replaced less than 2,000 miles ago. I have the other 4 NGK plugs for the driver's side but wasn't sure that the plugs were my problem, so I didn't replace them yet. I replaced the 4 on the passenger side because cylinder 4 was misfiring like crazy on a live data scan. I would think the coil packs would throw a code if they were faulty since they're electrical, but not sure on that. Are my plugs seriously bad again or can something else be causing the misfire?

 

Just based on my experiences alone, putting on 8 new coils would not be a waste of money.

The ecm doesn’t know if it is misfiring from a bad coil or bad spark plug. Low grade misfires like you describe will largely be ignored by the ECM leaving the driver to wonder what the problem is. Hard misfire events will cause the ECM to wig out and flash the check engine light, but it has to be pretty bad in my experience.

Your plugs should not be the problem.

It is likely either the coils or possibly fuel related.

Id try some good fuel cleaner first, then I’d start looking tat the coils. Dirty injectors are rarely a problem any more, but fuel cleaners are relatively cheap to try.

Just my humble ramblings

 

Looks like I'll be swapping out the coil packs then and see where that gets me. Been thinking about buying Auto Enginuity, especially for my 7.3l diesel, do you think that would help me better diagnose this problem as well?

 

Most likely you have carbon tracks in the boots from the old plugs misfiring. Now there are new tracks on the new plugs. A new set of plugs and new coil boots will fix it. The coils themselves are pretty robust and hardly fail.

 

I ended up taking the Expedition to the dealership since I have an extended warranty. They said it was the plugs, 6 out of 8 had gaps too large, but were not fouled. They also said the coils tested out just fine. I asked how I could have that many plugs worn so quickly, especially since I had NGK's on 1 side of the engine and Motorcraft's on the other. The NGK's only have approximately 2000 miles on them. They said nothing can cause the plugs to wear like that besides the plug itself. Sounds really fishy to me that 3 plugs with only 2000 miles on them can wear like that and nothing be the cause of it.

 

So what did they replace? Plugs and boots or just the plugs?

 

They didn't replace anything because spark plugs are considered maintenance and not covered under warranty. I literally just finished replacing all the plugs with new NGK plugs. The 4 Motorcraft plugs that I pulled out that had only 20,000 miles on them had gaps ranging from .072-.082 I ran a live scan and no misfires currently, we'll see how the next couple days go

 

Curious how this came out, and curious if the gaps were checked and/or set when the half-and-half plugs went in?

 

I did not check the gaps on the 4 Motorcraft plugs that I did not replace 2 months, but I did set the 4 NGK plugs before installing. The 4 plugs that I did not replace were not misfiring, which is why I didn't check them, plus they hadn't even reached 20,000 miles on them. I did replace all 8 plugs this time and set all gaps to .039 as recommended by the dealer technician. So far no more misfires or jerking of the vehicle. I did not replace any coil packs as the dealer said they spec'd out fine when tested.