My mondeo has a weird fault that defies the local mechanic: would like some advice on my next steps.

It runs ok, but when cruising the power drops in and out regularly - you can feel it and hear it in the revs, but the rev count barely moves actually - just a wobble if anything. It doesn't noticeably happen when accelerating or when coasting, only when cruising in gear - 40-50 mph.

It is smoking more than it used to do (I've had it a few years now) - white smoke from exhaust that comes out in puffs that coincide with the loss of power, every few seconds when holding it at a steady pace. Its like it putt-putts down the road! Also, periodically -particularly when putting down the power, (eg overtaking) - there are puffs of black smoke out the exhaust.

I thought maybe it was to do with fuel filter, but now changed and no difference. On other advice I dosed it with Redex for a few tankfulls, but that didn't do anything. Latest advice is that it might be a software fault, so I should get reloaded software at a dealership - however I'm not convinced - i still wonder if its mechanical and reloading software is an expensive red herring.

Just before all this started a fortnight ago I did notice that under power there was a new sound - like air rushing.

I don't mess under the hood myself, but want to be able to suggest something to another mechanic.

cheers

To be honest sean it could be a few things but try cleaning your EGR valve, check your boost pipes to and from your turbo and chuck something better in the tank than redex because thats crap.

+1

Redex strips all the good stuff out of the engine and turbo.

I recommend an additive called BG244, it's not the cheapest on the market but gets excellent reviews and results.

I would, like Rob stated above, have a good look at the boost pipes for splits, pinches and kinks, bear in mind that pipes can collapse under vacuum while driving and cause problems you can't replicate in a garage/on your drive etc..

A lot of people in the know fit sillicone hoses to their cars as they are more resistant to damage and don't tend to collapse and twist.

Of course this is all just my personal view, so if you're not sure the above will help, take it to a good diesel garage and see what they say.