406oc.co.uk

I am very disappointed to fined that my newly purchased 406 is only managing 45 mpg on our frequent Cornish trips, the old one which has done 246k manages 60+ when I drive it or about 55+ when my son does, both of these figures have been confirmed as near enough correct by brimming the tank.

The new one has only done 181k and drives and sounds spot on. The C5 I have been having problems with has finally given me a clue as to why it suddenly stops when you go to overtake, after a recent journey when it was frequently hesitating, when I got home I gave it a good rev and clouds of white smoke were emitted followed by misfiring, although now its cold OK its again. I suspect this is down to one or more injectors and am hoping that's what has been causing poor consumption on that one, the strange thing is the C5 is indicating about the same mpg as the good 406, whereas the new 406 is giving a fairly accurate read out.

I will do a leak off test on the injectors when it stops raining, if that is the problem and the consumption improves when I have rectified it I will try the same on the 406 - unless anyone has other suggestions.

Peter

I've always thought white smoke was condensation burning off, or in the case of a failing head gasket, water coming through from the
cooling system.

This was definitely unburnt fuel, you could smell it and there were clouds of it not just a puff, now its cold its behaving normally.

Peter

Leak off test is the first thing to try.

Do you still have the old 406 - maybe an injector swap,if you prove them to be 'leaky'?

I am intending to do that - when it stops raining. I have a set of secondhand injectors on the way, I would think there ought to be at least one good one.

Peter

Umm, mine is only doing 30mpg. And is gutless, Fwb didn't see anything on pp2000 that would do that.

Gutlessness is often the MAF although I don't know how that would affect the fuel consumption.

Peter

Ill unplug it tomorrow and take for. A spin, see if any better.

Mine has never done better than low 40's.

Depends primarily on how and where you drive, I rarely exceed 60 mph and drive mostly in rural areas, I used to get 50 mpg+ from my XM diesels on a longish journey and always 50 - 60+ from the 2.0 Hdi.

Peter