#4 missfire and iridium spark plug question

[jseabolt]

First of all which is the #4 spark plug on a 2006 4.6 liter V8?

Example: Drivers/passenger side, which one from the front?

So my wife calls me today and says the check engine light has kicked on and wanted to know if it was OK to drive it. I told her as long as the engine was not running hot and it had oil pressure to not worry about it and I would hook my code reader up to it when she got home.

So the code reader stored #4 missfire code, twice.

The engine does sound like it's still missfiring on a cylinder at idle some of the time.

OK let's back track to spring. So I purchased this Explorer last January and to make a long story short, it developed torque converter shutter. A transmission flush and new filter fixed that.

But to me the shutter felt like a missfire. So before having the transmission flushed, I pulled the plugs and they looked crappy. This vehicle had about 120K miles on it and the plugs could have been the originals.

Not long after a new plug change the engine started running worse but would not flash a code!

Finally the check engine light kicked on (on the way to the dealership of course) to have the transmission flushed and I told them to look at the missfire while they had it up there. He said it was a defective spark plug on #2 cylinder.

Out of all the spark plugs I have bought in my life, this is the first plug I have ever bought that was bad straight out of the box. You would think at $13 a pop they would be a better spark plug.

I've bought those cheap Chineese plugs for my lawnmowers that Wal-Mart sells and never bought a bad one.

So it seems one of spark plugs has went bad in 5000 miles?

Anyone else having trouble from these iridium spark plugs?

My plan is to swap the plug and see if it fixes the problem. If not, swap coils and see if it causes a missfire on that cylinder. Then I'll know it's a faulty coil.
If it still shows up on #4 cylinder, I assume that means a faulty fuel injector? Or does the missfire monitor pick up on a bad fuel injector?

 

[Ornery]

One of the few parts I buy OEM are the plugs. I don't know what magic happens inside these things, but I learned long ago that my Fords must have Motorcraft or Autolite. That's the best you can get for that engine, so if you got a bad one, that's just rotten luck.

I don't know how your dealer's scanner determined it was a plug, but I believe a bad coil or injector would throw the same code on your On-Board Diagnostics. If I'm wrong, I'll be corrected very shortly! Your plan of attack sounds good to me.

BTW, how did you get your plugs out?

 

[Flag Gibby]

I am with Ornery, I really doubt that it was/is the plug, but you didn't say what brand they are so I cannot say for sure (Champion is known for prematurely failing in these vehicles). I would say that the problem lies with that coil and maybe some of the other ones too. #4 and #8 are the ones that get all the water/moisture on them so those are the ones that typically prematurely fail, but since you are at about 120K miles I would replace all of them especially since you went the route of getting the more expensive iridium plugs not too long ago. FYI, while iridium lasts longer it actually has a higher resistance to the conduction of electricity so the plugs are actually more sensitive to coils that are breaking down and not providing as much voltage to the plug.
The Ford fuel injectors are very robust so I would be very surprised if there is any issue with the injector unless the connector is bad or there is a nick in the wire somewhere.

 

[thebrakeman]

When I had a misfire code, it was indeed a bad plug (swapped coils, and the code remained the same).