Not really drift.....;-)
OK, Ford wanted to extend service intervals when costs of service were included in the J D Powers cost of ownership surveys became relevant (they owned us, Volvo, at that time and we went through the same). They extended the plug service interval to 60K miles and to do this started fitting Iridium tipped plugs set at 1.3mm plug gaps. There never was much of an issue with the plugs but coil packs started burning out (think back to Ford Focus/Mondeo issues of the day). This was traced back to the following scenario, whilst the plugs were lasting 60K the gaps were increasing but not by much, however plug firing voltage (KV's) were significantly increased as the plugs reached higher mileages, this is normal. What is not normal however is how high the KV's reached, higher KV equals heat and the coil packs started overheating and failing.
Ford reduced the plug gaps in a TIB (Technical Information Bulletin-sent out to all dealers and so to us in Dealer Training) to 1.0mm and the problem was greatly improved. Later they sent a 'Red Top' (immediate action required) to all dealers stating that plugs should be changed at 40K miles, they did not mention increasing the gaps again back to 1.3mm?
The problem with coil packs stopped almost overnight for regular service cars, problem sorted. From this the advice we gave out at training (at that time I was responsible for Ford and Volvo training at Daventry) to dealers was its clear a belt and braces would be wise so leave the plugs at 1.0mm and change at 40K miles. Given the way we all over service our cars, and the difference is costs, I have for years (my Morgan and both Tin-Tops) fitted Platinum tipped plugs which are significantly cheaper, set them at 1.0mm (but that may be overkill) and changed them at 20K miles (definitely overkill)....coil packs remain cool.
Not sure about the Sigma service book, don't see it as very different from the Duratec as its just the clever cam gear that's different, I would use the same process as a Duratec so Magnatec 5/30, quality oil filter and NGK spark plugs. never been let down by that lot, there is not a lot else to do on the engine, valves don't need adjustment, fuel and ignition timing is ECU map controlled.....
