I am having mixed problems with my mpg, I used to be able to get 46mpg on a good motorway run taking it easy but these days I struggle to get to 44ish really trying. On Average I am loosing about 15% and I can't figure out why. It has been remapped by Ben at Shark Performance so In theory I should be getting even better then 46mpg.

I have had some problems with my DPF sensor, but (touch wood) that seems to have cured itself.

Now, on a long motorway run up to family this weekend I achieved 51mpg by sitting at a steady 65mph (traffic was fairly heavy so varied between 50 - 65 for most of the journey) and I thought the problem had sorted itself out! However after the service and on the way back I couldn't get above 44mpg.

Could disconnecting the battery & resetting everything effect the mpg? could it reset the ECU and by then driving for 30mins or so in town & stop start traffic force the ECU to programme itself incorrectly when dealing with the fueling? I am only guessing here but am running out of ideas! :(

First things last and all that

Tyre pressures ok? You weren't driving into a strong headwind on the low mpg run? Air filter clean enough? What's the DPF sensor fault, problems in that area could have the potential to slaughter mpg.

The computer could be inaccurate too. I'd be tempted to do some brim to brim calcs, confirm that mpg really is down. You don't have to drain the tank each time either, brim it, do 100 miles, brim it again, another 100 miles and see what you're getting really.

The trip computer can be adjusted (requires VCDS) if it's telling porkies. The other possibility is it was lying through its teeth before and now it's an honest so and so

Yeah, had the car serviced on friday, so everything should be tip top. It is a problem that seems to have occured over the last few months & d/c the battery has been almost a regular occurance with me trying to install a carPC in the boot. aside from the service nothing has changed the 51mph was over a 150mile drive so I didnt think it was a short term thing, just a shame it seems to have slipped now!

I guess I will have to try and brim to brim it and see what happens, urgh! Thank you anyway, any other advice is welcomed!

Well I cant really say with yours but I tend to find I get better economy cruising at 80+ than I do at 65/70.

Thats on the continent of course.lol

Trouble with all this electronics on cars nowadays, the basics get overlooked. If mpg has dropped for no real reason, first thing to check is that the wheels are going round without abnormal resistance.

Jack up each wheel in turn and turn by hand to make sure the brakes aren't binding for some reason on a wheel. Calipers can and do seize up.

Hi the recent cold weather has dented my mpg by about 5% getting around 46 to 48 on a mostly motorway run to work which is 25 mile commute at a steady 65 to 70 mph although i have the K and N panel filter fitted, this is using the brim to brim method.