Poorer than expected MPG

[marshall_rigger]

Hi i'm new to owning a audi had my current car for 4 months and so far i'm not impressed by the mpg tank to tank fill ups is averaging around 35-36 mpg, the car is a a4 b7 1.9 tdi 115ps avant. my daily commute is 18 miles each way along mostly A roads ( dual carraige way first few miles stop start up to tyne tunnel then genaeraly ok) i have changed the air filter fuel filter thermostat and coolant temp sensor but still no increase in the mpg. i have had the car checked for codes and there is no codes stored in the ecu to my knowledge the car is un modified. can anybody point me in the right direction as what to look at next. on a clear run the dis can show 40-44 mpg which is probably more like 36-40 in the real world.

could this problem be EGR related or possibly a MAF problem giving the engine ecu the wrong info.

[SammoVWT]

Sounds reasonable for the short-ish mixed driving. The start stop will eat your MPG. Plus its cold. And its a big car, and only has 115ps.

Dont be fooled by the illusion that diesel is significantly better MPG wise than petrol when in start stop traffic/urban driving.

[KrashBandiKoot]

I know it's a different animal but makes the point Sammo is making.

My SWB transit van is a 2.5 Diesel which on long runs does anywhere between 600 to 700 miles per tank full.

If I'm doing a lot of local driving and a lot of stop and start driving say through town or through road works this drops to about 400 to 475 miles per tank full. Diesels are brilliant for those long hauls where you can get up to speed and sit there at 60/70 mph for miles and miles on the motorway. But when you're talking about 36 mile round trips to work and back this is going to drop in MPG a hell of a lot.

[SammoVWT]

I know it's a different animal but makes the point Sammo is making.

My SWB transit van is a 2.5 Diesel which on long runs does anywhere between 600 to 700 miles per tank full.

If I'm doing a lot of local driving and a lot of stop and start driving say through town or through road works this drops to about 400 to 475 miles per tank full. Diesels are brilliant for those long hauls where you can get up to speed and sit there at 60/70 mph for miles and miles on the motorway. But when you're talking about 36 mile round trips to work and back this is going to drop in MPG a hell of a lot.

Agree with this, even on my ageing 1.6 around town (petrol), i'm hitting anywhere between 30-35 mpg on average and I don't always get up to 30mph in a slow manner. For a 9 gallon tank (appx) im looking at around 300ish miles per tank pottering around.

On the motorway which I did a couple of days ago, granted I had mostly a clear run both ways I managed about 145 miles to just over a quarter of a tank (2.5 gallons appx) which puts my range on 520+ miles appx. Not too shabby for a small tank.

Edit: Forgot to mention thats with a boot half full of tools and bits and bobs for work and the car etc.

[arman123]

Clean your egr valve see if you get any difference in mpg it's really easy three bolts off disconnect the electric plug and have a look at it bet it's full of carbon

[marshall_rigger]

egr cleaned and still no real improvements seen on a 18 mile commute to work averaging 33mpg calculated from fill up to fill up. when i fill the car the dis shows 560 miles till empty not good on a 70 liter tank on a recent trip along the a1 through a average speed camera zone doing between 30 and 40 mph in 4th car managed to show 46mpg on dis would be less in real world, but once back upto normal speed 60/70 mph the dis started dropping away pretty much instantly. the car is still showing no codes in vcds am tempted to let audi take a look and do some logs

[micheal balbrig]

I think you should expect 40-45 mpg,
Check the simple things that may cause friction first.
Brakes need checking for binding.
Tyre pressures need to be correct.
Steering tracking needs to be correct.
Air filter needs to be clean.
Good quality engine oil can reduce friction.
Engine needs to get to 90 degrees,although my thermostat is faulty for past few months and the differ in mpg is very little

[zollaf]

as well as what mr balbrig suggests, if that doesn't help, then get some data checked on the computer.its not all about codes. a cts can be out but not throw a code, as can the airflow meter etc...

[Col]

As above, especially fuel temperature readings.

[marshall_rigger]

i have a new fuel temp sensor to fit but have not got round to it yet bought it when i purchased the new coolant temp sensor and thermostat which are fitted all genuine audi components. i have tried a after market MAF but this made the car misfire around the 1800 rpm range only on acceleration then it would run fine not sure why ( after market MAF bought new from euro carparts). i replaced the old maf and car runs without any misfire. one thing i have noticed is that my boost pressure only went upto 1300mbar when accelerating upto and beyond 3000 rpm this was done stationery on my drive not under load using vcds to watch the figure. the boost pressure temp sensor is a new bosch item ( been changing some cheaper items in a hope to fixing the problem without expensive garage fees but its getting on my nerves now i know it should do better)

my tyres are kept at 34psi 235/45/17s
car has a full service history serviced not long before i bought it, i have renewed the air filter and fuel filter with bosch items.
the garage i bought it from checked for binding brakes when i asked them to look at the mpg. later just fobbed me off saying it was because of the cold weather.