What's causing a misfire on our Ford C-Max?

I have a Ford C-Max 2.0 diesel (80,000 miles, around 53/54mpg), which has always been main dealer serviced by the book. It suits us well and goes very well except that, for over a year, it has suffered intermittent engine jolts very like a misfire. These vary from soft, hardly felt, to quite hard. The dealer has not been much help. After a diagnostic check that showed nothing electrical, all they could offer was that I should drive it hard for a while and avoid short trips. But I already do this. I have a bus pass, which I use for most short trips. Most of my mileage is open A-roads or motorways.

Asked on 8 June 2013 by GR, Wormit, Fife

Answered by Honest John
The old C-Max 2.0TDCI is geared at 35mph per 1000rpm in sixth, and doesn't pull well at 50mph in sixth. It could be that at the road speeds you are driving the DPF is not properly clearing or the EGR is clogging a bit. It's worth trying it on Shell V-Power Nitro+. That might clean the fuel system up a bit and allow cleaner running at low revs as well as well as improve fuel economy by as much as 6 per cent.
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