[undecided1]

Originally Posted by CrocodileHunter

The only was to work out your true mpg is to start and end with a full tank as thats the only way you know exactly how far you have been and how much juice you've used

completely agree, if resetting the mpg then doing a short journey you'll get totally crazy numbers nowhere near what the car is actually capable of. Last time I reset my mpg then did a short journey of a few miles I was barely into double figures! If you so much as lightly touch the accelerator in 1st gear it swings straight to 12ish mpg so short journeys will always give terrible figures. You need to completely fill the tank and make a note of current mileage, then drive as normal until fuel warning light comes on, fill back to the top again and see how many miles you've done/exactly how much fuel it took to get back to full tank again - from these numbers you can calculate a more exact figure you can use to see if the car really has a problem or not. Using the inaccurate in car mpg reading (and then resetting and doing very short journeys) just compounds the inaccuracies and will give totally meaningless figures

[CrocodileHunter]

Although the on board readings seem to generally over read in all cars, I've noticed that they also seem to need a little while to settle down to what it believes is a true average after a reset.

When i first got my car i reset the average, then did some work on the engine and had it idling quite alot. It was only reading about 16mpg!

Since ive been using it for my 40 odd mile daily commute i reset it once more and now it sits at 40.3. It did take a few days to settle at that point though. I haven't remembered to check the true mpg yet. I will do so on the next fill up.

It was the same scenario with my wife's mk4 mondeo.

[Iyrix]

I've always tracked my mpg. Give a good reference to stats not working or driving hard...

[Benskett]

My 330d LCI (manual) gets around 550 miles to a tank, but that's motorway / DC with some hills.

On the flat it will do 600+

[Maxlude]

Mine is 2006 SE manual 120k now. Remapped to 275hp/450ftlbs. I get 48-53mpg on mways, 34-38mpg around town.

[MrSweet1991]

Hi All,

Well I've read through all the new messages and I just wanted to say a quick thanks for all the information you've contributed. I'm also going to take @lyrix idea of using an app to monitor my fill ups and MPG.

So I've been busy and have some more updates:

I initially changed the Air Filter and Crankcase Breather, both of which had no affect on MPG. (Averaged 21MPG)

The next thing I did was clean the MAP (Manifold Absolute Pressure) which didn't really appear to do anything but was definitely blocked up a bit. (21MPG Average)

Next I purchased some swirl flap blanking plates as well as Intake Manifold and EGR gasket sets, I then removed the EGR and Intake Manifold and gave it all a good clean and deleted the swirl flaps. I also pulled out the MAP (Manifold Absolute Pressure) and cleaned it again. Unfortunately and for some unknown reason I actually lost fuel economy after cleaning all of this which left me sitting at 19MPG average!

A few days ago I finally managed to get around to changing the thermostats, with the thermostats changed and reset my average MPG and took it for a quick drive and immediately I could see a difference in the MPG. From just a short drive I returned with 40MPG, now typically the best I've seen was 30MPG so I had high hopes that this has increased my economy by some margin.

I've covered quite some distance with these new thermostats and I'm happy to see that I'm now averaging 26MPG! It does fluctuate down to 25ish while cold but as soon as I get into the 80's it gets back into 26MPG so it appears that my town driving hovers in this region.

I know this figure isn't great but with the amount of hours I put into this car to see it making no difference or even reducing the fuel economy I couldn't help but feel very happy with this large improvement from 19MPG to 26MPG that's around a 30% improvement (and should reduce my fuel bills by around 30%)

Now that INPA is up and running my next job is to clean the MAF (Mass Air Flow) and use INPA to reset the adaptions. I've heard some people getting some good improvements in fuel economy from this.

Furthermore I also have a faulty code for a lambda probe heater which I believe can cause the engine to run lean and affect fuel economy. I need to do a little more research into this error but I'm on it.

So I'm heading in the right direction at least! And given the cars advertised as "Urban 31MPG" it doesn't seem too bad at all

[Digitalize]

Have you actually been working out your MPG manually or still relying on OBC?

If doing a lot of stop start driving then I could see Swirl Flap blanks reducing MPG. Good to see the advice many gave you on replacing thermostats worked, like it did for everyone else. If it's running lean you'd have higher MPG not lower, as it's not putting enough fuel in to create the power you want, unless you're full throttle all the time trying to compensate for the lost power.

[MrSweet1991]

Originally Posted by Digitalize

Have you actually been working out your MPG manually or still relying on OBC?

If doing a lot of stop start driving then I could see Swirl Flap blanks reducing MPG. Good to see the advice many gave you on replacing thermostats worked, like it did for everyone else. If it's running lean you'd have higher MPG not lower, as it's not putting enough fuel in to create the power you want, unless you're full throttle all the time trying to compensate for the lost power.

Hello,

At the moment no I haven't been working it out. What I tend to do is put in £20 of fuel and see how many miles I can get out of it. With respects to the relying on the cluster I know it really isn't good to rely on it because it can be in the region of 10% incorrect (well that's what I've read few times) but at the time I just wanted to see the figure improve and now it finally has. I will at some stage fill the tank and see what I can get out of it

Thanks for the the correction on the running lean bit, maybe it was bullet pointed and meant it could run lean or reduce fuel economy and I've just taken it as "running lean which reduces fuel economy".

What's your opinion on the sensor anyway? I can get a second hand one off eBay for around £15 (new are in the region of £80) but is it important? I've got a list of things to do on the car so I'm just working out a plan of action. I think I may do the MAF (Mass Air Flow) today and see how it goes.

Just a side note as well, when I put in brackets (Mass Air Flow, Manifold Absolute Pressure) that's just on the off chance anyone views this thread who aren't aware of what they are just in case anyone takes offence haha.

[Digitalize]

If the Lambda sensor itself is fine then it would only be wrong until the car is hot, the sensor isn't accurate until in its operating temperature so a heater is fitted to warm it up quicker than the exhaust gasses will.

I'm still standing by working out what your actual MOG is, mines been as much as 20% out, and as said the values can be altered to make them more or less accurate.

[MrSweet1991]

Originally Posted by Digitalize

If the Lambda sensor itself is fine then it would only be wrong until the car is hot, the sensor isn't accurate until in its operating temperature so a heater is fitted to warm it up quicker than the exhaust gasses will.

I'm still standing by working out what your actual MOG is, mines been as much as 20% out, and as said the values can be altered to make them more or less accurate.

Absolutely, I'll fill the tank and see what I can get out of it to finally understand what it's putting out.

As for the Lambda I'm not quite sure what exactly it's for so I'll have a good research about it. Also, It may be worth checking the connections, if I'm not mistaken the Lambda is on the DPF/Cat? I'm sure I seen it today and the wire runs towards the back where I've changed the air filter and crankcase breather.. that was one of my first jobs on the car and I have to admit I did give the air filter case a good yank as it was caught so I may very well have tugged on it.. time will tell I suppose