I had a new mechatronics unit fitted at the beginning of Janurary 2015, but since then my MPG has been a lot worse. I drive to chard to see my girlfriend every weekend which is a 40 mile journey and every time prior to having the new mechatronics unit fitted I would always achieve on average 45mpg. Now doing the same journey I'm lucky if I achieve 35mpg. I religiously have only used and still only use shell V-power fuel so it's not like it's due to changing fuel. I can't work it out, the only thing I have noticed is that the program they have uploaded to the Mech Unit seems to be very economy focused and only wants to change up to 7th gear even when at low speeds whereas before the new Mech unit the car used to be a bit more sporty and would hang onto gears longer which would give me more torque more of the time. Any ideas ????

It is winter,

is it cooler now than before your MCU was changed.?

 

So what age and mileage of car.

How long have you had it before the Warranty Work was done?

 

Maybe give the car a bit of a thrash and see if it learns your old style of driving.

use the DSG in Dynamic Shift programme.  see page 101 of the owners manual.

 

It sounds like the way it works now should be more economic, not less.

Have you adjusted or checked your tyre to suit the colder weather?

 

PS

If they had to change your MCU i take it there was a fault, so what was the fault, 

because a new MCU really should not be acting like a faulty one did.

 

Maybe ask the Dealership that did the Warranty work if as well as the DSG Software update,

is the Engine running the latest Updates.

Edited 6 February, 201511 yr by goneoffSKi

Had the car 6 months and it's an 11 plate car 40k on clock. Mech Unit just died after 6 months of ownership and wouldnt select a gear. Was replaced under extended used car warranty. tyre pressures are always kept at 35 psi no different from before work was done. I get what your saying about it being winter, but I read somewhere that at cooler temperatures engines work better (more powerful) as the air being fed into the engine is denser.

That is right, you might even get better consumption on runs when you have cooler air so more efficient running

and cooler roads so less friction of the tyres.

 

But on shorter trips it can take longer to get the car up to temp,

so if on a journey over 20 miles the consumption is down, then you might wonder why.

Even though you kept using shell the Fuel changed late October to winter spec.

Changes back in March. 

Tyre pressures need checked as the temperature changes, because they do a little.

 

The common reason for fuel consumption changing can be as Spark Plugs need changing.

?
have yours been changed in the cars life?

40,000 miles is the scheduled change, if not already done.

Edited 6 February, 201511 yr by goneoffSKi

Didn't realise fuel is changed, why is this???

Yea spark plugs where done prior to purchase of the vehicle at 35k.

The formulation changes to make it less hygroscopic.

in Scotland and the North of England usually from about the 15th October to late October it gets delivered to filling stations.

down south maybe later.

Oh right didn't no that.

So I'm really best asking dealer about engine updates first to check I've got the correct ones then if that's ok waiting to see if my mpg goes up in March when the fuel changes back.

Failing that it's a mystery!

When in "D" check if gears are shifted at 2k rpm when you drive economically. If not there is sth wrong or the box has not learned yet - less likely.

My vRS (Nov 2012 CTHE) summer time returns 35-37 mpg. Winter time on the same routes 10mpgs less.

Edited 12 February, 201511 yr by Jabozuma

Thanks Jabozuma

Yea it shifts at around 1800 rpm, so I'm hoping it's just a mixture of it being winter and the fuel change like George said. Just thought it was weird because mechanically nothing has changed just a computer component.

Thanks again guys :-)

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