I was actually looking for another forum post of the Ford world but then I found the link below.. I also have Iridium spark plugs in the 4/4, I don't know the exact name at the moment. But at that time, around the end of 2014, it was already discussed that Ford had chosen smaller electrode distances than at the beginning of production to protect the ignition coil. So you are on the safe side, but you might give away some performance.
https://www.fordownersclub.com/forums/topic/39946-electrode-gap-on-16-engine/#comment-231065At that time I noticed that my Iridium spark plugs recommended in a comparison list had a different electrode gap than the copper spark plugs. But I don't know if this was an equivalence value between iridium and copper or if the iridium spark plugs had a slightly larger electrode gap for other reasons.
The last post on this page was interesting for me because I think that this post about Ford corrected electrode gap is younger than my knowledge.
I will definitely check it myself which spark plugs I have because somewhere are still the old boxes or the invoice.
Please note, the 4/4 machine will not be called Sigma in this last post but Duratec 1.6 VCT TI
Do others here in the forum have more current information than I do? That would be very helpful. I would think that the 1.2 mm specified in the last post for standard spark plugs sounds plausible. But I will check this again or call my Ford dealer.
Because with exactly such information it is often better to ask the company that produces the engine and not the company that installs the engine.
