MPG worsened drastically, likely cause?

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chrisru

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I do a number of regular trips up and down the motorway and usually get around 38mpg rising to just over 40 on a longer trip if I'm not pushing it too hard. This has been very repeatable over the car's 2 year history with me, especially for some of the regular routes, which I do over and over. In the last couple of months that average has worsened and now I get 35mpg at best, 33mpg yesterday. The car runs without obvious issue, maybe down on power. It's just been serviced by APS and there was nothing reported.

I'm thinking of getting it on a rolling road and having someone analyse the exhaust gases, any other suggestions as to possible causes or investigative techniques?
 
chrisru said:
I do a number of regular trips up and down the motorway and usually get around 38mpg rising to just over 40 on a longer trip if I'm not pushing it too hard. This has been very repeatable over the car's 2 year history with me, especially for some of the regular routes, which I do over and over. In the last couple of months that average has worsened and now I get 35mpg at best, 33mpg yesterday. The car runs without obvious issue, maybe down on power. It's just been serviced by APS and there was nothing reported.

I'm thinking of getting it on a rolling road and having someone analyse the exhaust gases, any other suggestions as to possible causes or investigative techniques?
Click to expand...

I too have noticed similar on mine, I did a 150 mile trip and drove for economy and only got 38mpg. I have also noticed a drop in my daily commute. I serviced mine a couple of months ago. Strange!!!
 
Cold weather, sitting in queues,...

In the summer I get 22mpg on my commute but in the winter I get 18mpg - all down to the engine taking longer to warm up and hence running a richer mixture for longer.
 
Thanks Dave, you're right there are a number of reasons why I'd get worse economy but I haven't noticed it in previous winters and that's quite a difference. Having now become a bit obsessed with this, I've tracked a couple of recent trips up to North Yorkshire, this was on the motorway almost entirely and include that chunk of the M1 around Nottingham at a very economical 50mph - still got 35 mpg.
Any suggestions for someone in the Midlands with Audi tuning experience and a rolling road - keen to have it tested before the next MOT in case it isn't running within limits.

Chris
 
I would say it is most likely the cold weather. Sitting waiting for screens to defrost, ecu adding extra fuel for longer, heater on higher etc. I know oyuve said you didnt notice before, maybe your just more aware this time round...?
 
I decided to check whether I had any problems, I found Monster Motorsport http://www.monstermotorsport.com/ at Loughborough who have a 4 wheel rolling road, on which you can do a run for £50. The results are below (assuming I get the tags correct) - 206PS and 474Nm which are both slightly above spec. Maybe my wife was right - I have the car equivalent of hypochondria. Anyone know what the correct Air Fuel Ratio should be for a 3.0 TDI A4 - it seems to vary from 19 to 23 from the graph.


hpandlbft.jpg


afru.jpg
 
Diesel powered cabin heater coming on on every cold start ( providing you have your CC on Auto ) will use quite a lot of extra fuel but its worth it !
Ian
 
Do I have a diesel power cabin heater, I knew it was an option in Germany but didn't think it was in the UK. The car does heat up reasonably quickly but it still takes a few minutes so I suspect I haven't got one. Be interested if anyone knew how to fit one, especially at the moment.
 
As far as I know most of the diesels here are fitted with an electric auxillary heater that heats up the interior quicker when its cold, mine comes on if the climate is on auto and its 4.5 degrees or lower, being electric its not long before you feel warmth. The diesels being as efficient as they are naturally take longer to warm up especially when cold, running richer for longer, the alternator takes a pounding too this time of year, charging a cold battery, heaters, fans, demisters, lights.........
when it gets milder you'll be back to normal....
 
I thought the cabin auxiliary heater was Diesel powered ( if it was electric the current consumption would be enormous ) and made by ebac ? who can supply kits for trucks and cars , I was told that most Audis ( Tdi ) Have them .
Ian
 
I thought the cabin auxiliary heater was Diesel powered ( if it was electric the current consumption would be enormous ) and made by ebac ? who can supply kits for trucks and cars , I was told that most Audis ( Tdi ) Have them .
Ian
 
Perhaps you are thinking of Eberspacher who I think make the auxiliary pre-heater for Audi. I don't think it's an option in the UK, but it would be nice at the moment to start up a car with a warmed up engine :sm4:
 
Hi Chris

I have the same engine, the handbook does say that the diesel engines have a supplementary heater that runs as described above. I normally get 450 miles to a tank, this one 3/4's is gone and I've done 270!

I put it down to the cold, queues and warming it up while scraping the windows.

Nice result on the rolling road.

Are you local to Nottingham?

Chris
 
Yes nice to see that the car isn't down on power at nearly 5 years old. I'm just south of Loughborough, near to Ashby de la Zouch - hence the wonderfully named Monster Motorsport are quite close. I did look at fitting the Kenlowe preheater, but nobody seemed confident as to where it should be plumbed into the system - you can then put it on a timer and have a ready warmed car in the morning. http://www.kenlowe.com/pre-heaters/cars/index.html
 
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