35 38 38 37 38 39 . swapped to 6510s at 35. idles smoother, accelerates with no hesitations mid rev. will see how mileage suffers.
all my plugs were GROSSLY over torqued from the factory. nearly twice the factory torque specs on one of them.
Did mine this morning, and they were also WAY over torqued as well.
I checked one plug last week and it was spot on .035 so I wasn't sure if I wanted to mess with the rest or not, but I decided to go ahead and do it this morning. Good thing I did, all but the first plug I checked were improperly gapped. .035, .042, .039, .037, .039 .040
Couldn't tell much of a difference at idle and I won't get a chance to take it for a test drive until this evening, but I've got my fingers crossed it helps the shudder.
Copied my post from shuddering sticky in 2009+ forum:
After the weather and temp fluctuations this past weekend during a torrential downpour, I had a power loss event and severe shaking while attempting to pass someone.
I'm almost convinced this problem is severe spark quenching. Especially after seeing the improvements the guys have been having reducing the gaps on the OEM plugs.
I've run into this problem a few times on other vehicles, both turbo and NA with various mods, it is nothing new nor specific to the Ecoboost. Ford is probably aware of this but until they nail down the exact source of the issue, there is no point in throwing more (expensive) parts and labour at the problem until the supply chain/engineering issue is resolved.
My problems aren't as severe as others appear to be, although I will soon be changing out my plugs, probably to an NGK dual fine element iridium type and gapping them somewhere around .034"
The eventual permanent fix for this from Ford may be a change to the plug specs, an upgrade to the ignition coils, or both. If you have some time and money to throw around, maybe someone could experiment with these changes and report back!
Interesting, after reading this entire thread over lunch, I need to find time to check mine and see if my imaginary misfire (dealer doesn't feel it,and doesn't code) goes away. And hopefully I can do better the 16.5 miles per gallon.