Two days ago my Opel Corsa D LPG's engine started to misfire, and by means of an OBD interface I found out it was cylinder 1.
First thing I thought about were the spark plugs, as I haven't changed them in the last 36k-40k kms. When I took them out, though, I found them quite clean and not corroded at all. Plus, I've measured the gap with a makeshift thickness meter and they seem ok (1.1 mm, as spec'd).
Today I've checked the coil pack with a multimeter and it seems that cylinder 1 coil is broken (others show 15MOhm to common, this one seems an open circuit). So I'm going to change the coil pack, but I had it changed few months ago, after a similar failure (I didn't do it myself then, had the car repaired by a shop since I was far from home).
Now I'm thinking of blaming the shop for not completely fixing the fault, but I'm wondering: could the cause be the (relatively) wide gap of the spark plugs? Other recommended parts for my model have a 0,7 to 0,9 gap instead, and I suppose this limits the peak voltage of the discharge, thus (I suppose) stress less the coil (beside other effects).
Current installed spark plugs are NGK ZFR5F-11, some sites indicate Bosch 0 242 235 666 as a possible replacement. Couldn't find any recommendation by Opel itself.