Poor mpg and smoke

[jml]

Recently the fuel consumption of my 2.2HDi 173hp has dropped by about 20%.
I’ve noticed that, after cruising, when accelerating a plume of black smoke is emitted.
On Diagbox, absolutely nothing shows up and, although I don’t recollect the exact figures, when I looked at the DPF all seems well.
The car drives perfectly.
MOT a couple of weeks ago and the (smoke ?) limit was 0.15 whilst my car measured 0.00 !!

Any ideas as to causes of plummeting fuel consumption and smoke ?

Cheers

Julian

[Hell Razor5543]

Black smoke normally means improperly burnt fuel, which is usually down to poor airflow into the engine. When was the last time the air filter was changed?

[jml]

Thanks, good point. I’ll check when filter was changed although, despite the mileage of 166,000, I do stick religiously to the manufacturers service recommendations.

However, if it was the filter, wouldn’t it smoke at other times ? And, as I mentioned, performance is unaffected and it seems to run really well !

Cheers

Julian

[mickthemaverick]

Just a thought Julian, as James says black smoke is usually unburnt fuel as a result of too little air. As the car is driving normally then you may have a case of the right amount of air but overfuelling which would also account for the poor mpg. If you have a worn or damaged injector it can cause overfuelling as the aperture through which the fuel passes can get enlarged allowing more fuel through and then ejecting the half burnt surplus through the exhaust as black smoke, so if your filters are clean and the air ducting is clear I'd run a diesel overflow test with four bottles connected to the overflow pipes of each injector and see if the results are balanced. If one injector has noticeably less overflow then that may well be the one putting too much into the engine. Good Luck

[jml]

That’s very good thinking, thanks Mick

I’ll do an overflow test, as you suggest.

Cheers

Julian