Wow, thank you for the very helpful insights. Yes, 70F100, the engine compartment is darn near showroom. And I swear the stutter is getting less frequent and less severe. Is it possible that if they got water down in there it will just evaporate off and nothing else will be needed?

Been out of town and away from computer and vehicle for three days but will check hoses and manifolds above heads for drips this evening.

$10k is more than I paid for the vehicle, so as awesome as that scanner may be, I wouldn't say it's exactly a viable solution.

Finally, even assuming this has something to do with water intrusion and further assuming the symptoms clear up on their own--are you all saying I should go ahead and change the plugs based on mileage alone? Sounds like that's kind of difficult and delicate process--would you recommend taking it to a dealer for that, as opposed to an independent shop?

 

You could check with the seller to see if they've already been changed. Not everyone waits the full 100K miles before changing them. Considering the difficulty in changing them, I for one would rather make that phone call first.

 

I bought from a small-time dealer, not the owner. But the previous (and original, according to Carfax) owner was allegedly an acquaintance of the dealer. Trying to get the dealer to put me in touch with the owner, but don't have the highest of hopes.

 

The owner might not be receptive to that, but the dealer could always ask the question for you and let you know the answer.

 

I would go ahead and pull a plug or 2 and see how they look. They tend to break less when the engine is hot. You dont want to keep driving it with it skipping

 

I've tracked the misfire to cylinder #8 (unfortunately, since I gather that's the toughest one to reach). There may be others misfiring that I'm unaware of, but because of budget constraints I'm going to go ahead and replace the COP and boot on #8 to see if that clears up the stuttering.

So my next question is which coil/boot assembly I need to buy. Strangely, there's quite a bit of disagreement between the various automated compatibility widgets on the Ford Parts site and other retailers. Some say the 2005 takes a DG-508 (the one with a small angle in it). Others say it takes a DG-511 (straight).

Anyone happen to have a firsthand knowledge? BTW, I am buying Motorcraft, not aftermarket. Just don't know which Motorcraft to get.

 

I'm having these same issues and same cylinder. It's best to replace all plugs and coils. From what I've read this is a common problem and will continue to be a problem.

 

If you are facing budget constraints, swap #8 COP with #7, swap #8 boot with #6, and swap #8 plug with #5. Then retrack the misfire and only change what shows up as bad.

 

You could always pull out an easy one and see for yourself, but according to fordparts.com you need a DG-511.

2005 Ford Expedition COP

 

I'm sure this being 3 years ago this guy has addressed his problem. But the exact same thing happened to me, I had bought the truck with 108k, and assumed the dreaded plugs had been done, so I did coils and nothing. When I would get on the highway I couldn't get out of my own way due to misfiring. it was the sparkplugs, they had been changed and were bad again,

 

I have the same issue with my 2003 expedition. I'm the original owner and have a very good feel on my foot. I drive this vehicles less then 5k miles a year but it looks and drives like new. however I started feeling a slight miss when taking off at green lights. so slight that no one else in the car could feel it. Lately this miss has gotten much more noticeable but it is intermittent. No engine light on. I thought it was a coil myself. In order to test these coils they have to come off and be individually tested with ohm meter. If I have to take them off like that wouldn't it be smarter to just put in all new ones? A set of coil is what around $50. Any other advise that might work

 

Depends what coils you buy. Motorcraft are around $70 each. A not uncommon culprit in this is actually the coil boots, and they can be had for a few bucks each.

 

The MIL will only come on if the rate of the misfire exceeds a certain threshold. Misfire rates under that threshold will not set a DTC nor will set the MIL to on.

Testing coils with an ohmmeter would be a waste of time. That would only show a gross failure (which would not exhibit as a mild or intermittent misfire).

The best method for a DIYer to diagnose a mild misfire remains using a scan tool or equivalent that can display the Mode $06 data and look at the individual cylinder misfire counts. An Android device, a $20 OBDII adapter, and a $5 app is all it takes.