Superfragilisticexpialigocious

I'm on my second Mondeo 2.5V6. I've run them both on ordinary unleaded but at about 68k miles (now 72k miles) my car developed a misfire at low revs when the engine is under load. The car still starts well and is unaffected by wet or dry weather. Plugs have been changed and I was about to change HT leads when I discovered that the misfire got better or worse depending on where I filled up. I tried Superunleaded and the misfire went away almost completely. Has the quality of unleaded been reduced recently so that my car will no longer run properly on it? Or is the superunleaded masking an underlying problem? HT Leads? Knock sensor?

Asked on 28 August 2010 by DM, via email

Answered by Honest John

There is no substitute for Shell V-Power. Not just my opinion, I have proved it. After my 'economy' driving lesson in Paris on 5th June I noticed that the mpg of my FIAT 500 1.2 petrol was improving steadily, from 53.3mpg to 54.5mpg. But this was over the last 200 miles of 1,000 miles in Trip A. So I re-started trip B and was astounded to see 67.2mpg over 27.1 miles, later falling to 64.2mpg over 122 miles cross-country. By allowing the engine to run cleanly at low revs, that's what V-Power can do.

Tags: technical issues spark plugs owning

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