# 2008 2.0 TFSI (BWA) - Poor Fuel Economy...?



## Rustbucket (May 6, 2021)

My 2008 BWA engined car has been great on petrol all the years I’ve owned it. I get 40-42mpg on a motorway cruise at 70mph and about 32mpg around town. Recently the economy has dropped to 34mpg on the motorway and 28mpg around town. The economy on the motorway is currently the same at 90mph as it is at 70mph whereas previously you would see a drop in mpg at higher speeds as you would expect.

the car has 85k miles and full service history. It’s very recently had a service including new plugs, fluids and filters. Performance hasn’t changed and it runs great.

ive Checked under the bonnet and everything looks fine and there are no leaks or obvious issues. 

I’m not getting any codes through my obd reader (although this is a cheap device).

the problem appears to have arisen at the same time as my Bose amp dying and also my original battery finally losing its grasp on life in the recent freezing weather. I’m sure that is just a coincidence but thought it worth mentioning. I’ve also noticed that the car is slow to catch when starting if left for a few days, which may be related to the failing battery or possibly the lift pump being in its death throes.

does anyone have any advice as to where the issue may lie/what to look for?


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## TT'sRevenge (Feb 28, 2021)

Those number still seem amazing to me lol. I can't even get to 20 MPG US at absolute best in the city (so less than 24 MPG Imperial, more often around 22). Highway if I'm very lucky I can get to 30 (36 imperial), but more commonly I'm at 27-28 (33-34 imperial).

Is yours a FWD? Because your higher/older numbers seem incredible to me lol--40 imperial is like 33 US and never have I seen anything even close to that.

Anyway, these are all the things I've done to try to increase economy--some made small differences, like maybe 1MPG US if lucky but I think I pretty much covered all the bases myself:
-Full intake-off carbon clean of the intake valves and ports; injector clean (this is one of the earlier things I did after buying the car)
-New ignition coils
-New fuel filter
-New air filter
-Adjusting tyre pressures, anywhere from +5 to +10 psi over factory pressure (made a lot less difference than I expected)
-New spark plugs just recently, similarly minimal difference

I've kind of called it a day now on trying to get better FE as I think it's all just my own fault in the way I drive lol, but given you've had better FE in the past and your driving style has not changed, seems something must be amiss...

When was the last time you had the intake off to clean the intake deposits? Also you mentioned new plugs but not coils--have those ever been replaced? As for the low pressure (tank) fuel pump, if the car idles fine and drives fine normally, you'd probably want to drive under high load--high RPM and throttle/acceleration, to see any weaknesses there. If there's no issues with fuelling with some hard pulls, full acceleration, I probably would not suspect the low pressure pump is an issue.


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## SwissJetPilot (Apr 27, 2014)

Might be time to take a look at carbon buildup on the intake valves.  These are generic "before and after" pictures when walnut blasting the valves.


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## Rustbucket (May 6, 2021)

Thanks for the feedback. It’s a 2WD car and I’m reflecting on a gentle driving style on my 28 mile commute to work. The best I’ve seen driving like a priest is 43mpg. I only use the car 3 or 4 times a month to go in to work now thanks to the pandemic and so the change in economy is noticeable over a month. If it was carbon build up I would expect gradual decline in economy over many miles. Similarly if coil packs were failing wouldn’t you see a gradual decline?

the only things I haven’t changed are coil packs, fuel filter and pcv system, which may be originals.


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## Barr_end (Oct 19, 2016)

There maybe a fair few things that would cause this, I have a couple of theories, but would need to know the information to the below..

Was it serviced, then you experienced the lower mileage?
Does the car still reach and maintain 90C coolant temperature on the dash? Anything over 50-60mph does it drop away from 90
When you say the OE battery died in the cold - had no power and you jumped it? Or did the battery get replaced
Has the car ever been mapped, if so by what company?

Additionally would be interesting to see what you actually get mileage number wise from same amount of L of fuel, rather than just using the dash MPG read out


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## Rustbucket (May 6, 2021)

Hi all good questions and here are the answers. 

The car was serviced in July 2022 about 500 miles ago. It had fluids, oil and air filter, plugs as well as brake fluid and new stainless braided brake lines. It was all fine up until November when I noticed the drop in economy on the OBC. I’ve been tracking the situation since then and have recorded 270 miles that for the same amount of petrol I would expect to see 300-320 miles. I only use shell V power BTW.

car is bog stock standard and has not been mapped.

the temperature sits at 90 degrees at all speeds. I know that a faulty thermostat can cause poor mpg as this happened to me this time last year. I replaced the thermostat in Spring and normal service was resumed. If I’d not replaced the thermostat and didn’t have normal operating temperatures I would have put my money on this being the issue as the drop in mpg then was the same as experienced now. I wonder if there are any other sensors that might inform the ecu to enrich the mixture?

the battery hasn’t failed yet and I haven’t had to charge it…yet. It is on borrowed time and I was advised it was at 60% efficiency at the last service. However it has been struggling in the cold this winter and I noticed the other day turnover was very slow. This is more noticeable lately because it is slow to fire up if left for a few days.


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## Jezzie (May 24, 2020)

Rustbucket said:


> It is on borrowed time


Replace it now! It's going to last for years so don't suffer this winter thinking you're saving money. We're talking £80 for a really good Varta (as factory fitted) from TAYNA
Jez


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## Rustbucket (May 6, 2021)

Yep the battery is on the list for replacement- just trying to get hold of one locally at the mo. My obd dongle for the Xtrons radio probably hasn’t helped battery performance either.


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## Hoggy (May 8, 2002)

Hi, Could it just be the colder weather. Does the coolant temp reach 90 within a few miles & stay there whatever the road speed?
Tyre pressures correct?
Hoggy.


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## Rustbucket (May 6, 2021)

Hi Hoggy. Yes temp goes straight up to 90 degrees and stays there whatever the speed. Tyre pressures are perfect.

I’m thinking this is could be a sensor issue- something telling the ecu to enrich the mixture? Electrics are not my bag so I’m struggling to think what it might be


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## Rufflesj (Jun 22, 2020)

Check your calipers aren't gradually starting to drag, this happen me a few years back with the same drop off on mpg. Can't imagine how you're getting that mpg figure around town!


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## Hoggy (May 8, 2002)

Rustbucket said:


> Hi Hoggy. Yes temp goes straight up to 90 degrees and stays there whatever the speed. Tyre pressures are perfect.
> 
> I’m thinking this is could be a sensor issue- something telling the ecu to enrich the mixture? Electrics are not my bag so I’m struggling to think what it might be


Hi, Coolant temp low will enrich the mixture but coolant temp appears O.K. EGT sensor registering high would cause rich mixture.
Perhaps a VAG specific scan is required if those MPGs are correct.
Hoggy.


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## Rustbucket (May 6, 2021)

Thanks all for your contributions. Brakes are all new. Is the ‘EGT’ the exhaust gas temp sensor? Is it possible to test this without a vag code reader?


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## Jezzie (May 24, 2020)

Rustbucket said:


> Yep the battery is on the list for replacement- just trying to get hold of one locally at the mo. My obd dongle for the Xtrons radio probably hasn’t helped battery performance either.


As said - buy online from Tayna with next day delivery. Brilliant service!


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## Barr_end (Oct 19, 2016)

Rustbucket said:


> Hi all good questions and here are the answers.
> 
> The car was serviced in July 2022 about 500 miles ago. It had fluids, oil and air filter, plugs as well as brake fluid and new stainless braided brake lines. It was all fine up until November when I noticed the drop in economy on the OBC. I’ve been tracking the situation since then and have recorded 270 miles that for the same amount of petrol I would expect to see 300-320 miles. I only use shell V power BTW.
> 
> ...



Unfortunately that has debunked the majority of my speculation 😅

As Hoggy alluded too - cold weather in general does have an affect - as you had already answered the thermostat question..

I don't remotely remember the numbers as it was years ago - but when my TTS was a daily, sub 10-12C ambient temps would 100% affect the MPG would seem much worse on the dash!
I can't remember if this also actually ended up with a mileage difference from X amount of fuel though!
The 10% difference on this with yours sounds a noticeable amount which I think could be more than just temps

As other have stated 'failing' rear calipers are the next go to, I see you said brakes are new so assuming you didn't mean just discs and pads
Sound like the type to... But with the cold weather did you also adjust tyre pressures accordingly too? 🤔 

Past that I'm all out of ideas... I don't think the economy you're experiencing is abnormal or poor though - so maybe the true answer is just turn the screen back to speed output and enjoy it


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## Rustbucket (May 6, 2021)

Thanks everyone for input and support. There’s definitely something going on and I will get to the bottom of it with time and report back. It may take a few weeks because it’s winter here and I don’t like working on it in the rain and cold and I don’t use the car often enough to worry about mpg.


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## TT'sRevenge (Feb 28, 2021)

SwissJetPilot said:


> Might be time to take a look at carbon buildup on the intake valves.  These are generic "before and after" pictures when walnut blasting the valves.
> View attachment 495610


Haha that "before" picture is funny. That's a VAG 2.0T engine after it has gone like 5,000 miles probably? The _real_ before pictures on one of our engines will be much...MUCH worse than that. That "before" picture is basically super clean


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## SwissJetPilot (Apr 27, 2014)

Oh I'm sure I can find a worse one..  Happy now...


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## darrylmg (Oct 16, 2021)

TT'sRevenge said:


> Haha that "before" picture is funny. That's a VAG 2.0T engine after it has gone like 5,000 miles probably? The _real_ before pictures on one of our engines will be much...MUCH worse than that. That "before" picture is basically super clean


I'm glad you said that. 
I'm considering doing a bit of scraping in the summer.
I was put off by how clean that "before" picture looked. But now I'm back on to thinking about doing it.
👨‍🔧


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## TT'sRevenge (Feb 28, 2021)

SwissJetPilot said:


> Oh I'm sure I can find a worse one..  Happy now...
> View attachment 495947


Haha yep that one seems more accurate. Now I've not seen one that bad myself (in person) yet, but that's a lot closer to what it will look like for most when they remove the intake than the former picture  I think this^ picture is after some scraping was done though as you can see what look like scrape marks on the valve stems.



darrylmg said:


> I'm glad you said that.
> I'm considering doing a bit of scraping in the summer.
> I was put off by how clean that "before" picture looked. But now I'm back on to thinking about doing it.
> 👨‍🔧


It's a dirty and time consuming job, but well worth the feeling when you get it done. Note that you probably shouldn't expect results like the right side either, because that was achieved with walnut blast. I've not been able to get one quite that clean with just physical scraping and drill brush attachments (which is how I've cleaned the times I've done it). Though the next time I do it I'm going to try the plastic-zipties-in-the-drill-chuck method to see if that does any better as I didn't try that. Also might give the Piston Kleen a try though reviews I've read are mixed--worth a shot to see for myself though.

You can see in this thread from when I bought my TT, the before state, the cleaning, and the after--sorry I should have used more light to take the pics but oh well...








Carbon on intake valves after 185k km...


So since I'm waiting for some parts to put the oil pump/balancer and pan back on from the other thread, I moved on to the next "fun times" project in the mean time lol. Pulled the intake, doing a carbon clean now. There's lots of similar pics to be found on the intarwebs but I thought I'd...




www.ttforum.co.uk


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