Odd MPG figs - since service & wheel bearing change.

[nc35]

Hi All
Last month the car had a full long life service, cambelt water-pump, air con, brake service & both rear hubs changed.
To be honest the car drives better much smoother, quieter etc. 
But the MPG has dropped from an average 33-35mpg to 26 at best.
Same driving etc etc.
Any ideas or are my new shoes heavier???

[tony_danza]

Coincidence? Not plugged the MAF in correctly or MAF being faulty would be a place to start, then check all vac pipes etc.

[nc35]

Thanks for the quick reply.
Ok - engine cover off in the morning.
Stupid question - how many vacuum pipes are there? K03 AXX engine.
Then re-check the MAF sensor is plugged in correctly.

Can any of this be logged with VCDS?  New user not too sure what all the settings are yet.

[john_o]

obvious check would be flat tyres 
on the basis of what youve had done , worth checking for binding brakes too
(hot alloys to the touch where youve not braked heavily/blueing on discs)
as mr d states , looking for a vaccum leak
you can measure actual boost measure but at idle , the value is based on atmospheric at the time being 0, so roughly 1000mb is 0, anything below is a vaccum.
so expect to see a value of 250 millibar recorded which is 750 difference
(750 millibars = 22.1500295 inches of mercury), which is what I see on my boost gauge at idle  *
(* this could of course all be wrong  )

[nc35]

Cheers John_O

Bit of an anorak when it comes to tyre pressures.  Checked everytime I fill up.  If there is any significant change (+/- 1 bar) double checked with digital pressure gage.

Will get VAGCOM out again tonight.  To check the actual boost at idle...  Should take me a few hours working out how 

Then I will jack the car up and spin the wheels, looking for any difference.  Gary (who fitted the hubs on the side) did a quality job (I think) as he let me watch and learn as he did it.  Not much to learn really.  He did clean up the calipers and pads before re-lubing with the silicone stuff.  So hopefully they shouldn't be binding...

Finally - if I am checking the correct bit.  The MAF sensor is on the back left of the engine cover (as you look at the car from the front).  The lead is securely attached.  So don't know what more to check....



Should have put in the original post the fuel economy is a little random.  Just driven to Harrogate and got (according to the dash readout) 38.2MPG.  Same run last week was 16.2MPG.  Normal  commute into Leeds ~ 26MPG depending on traffic etc.  Seen lots of mid teens and a few low 20's but nothing near 26MPG  apart from one random 32MPG.

Could a failing Coil Pack, spark plug or MAF sensor give intermittent MPG?

From memory the only concern I have had was hesitation pulling out from a junction a little too quickly.  Could have been TC kicking in or the orange engine warning light.  Just eased off the gas and everything was OK in an instant.  (BTW never had TC kick in yet - call me Granny)