cdti improve mpg
 

Hi all have two cdti s manual saloon 135bhp returns 45+ mpg mainly motorway,
and auto tourer 115bhp 36mpg on the same run, was thinking of having the ecu programed to 160 on the auto anyone know how much improvement to fuel consumption, or are their better options
Cheers

I have 2 160's and they both get 45-48 on a run, 36-42 urban

First thing I would be checking is that it is getting up to temperature.

yep,

correct temp (circa 84-90)
Good air filter, PCV filter, Maf in spec, no tuning box to cause overfuel, good oil, good tyre pressures etc.

Using onboard computer manual 87
auto 89/92 but the gauge is on max with red light on

Fuel consumption has always been a bone of contention on this any many other forums.


It will always depend on several factors,Car up to temp,type of roads used,The driver,how well the car is maintained and how big a foot the driver has.


Many will claim astronomical mileages of 60 + per gallon and others will complain of low forties.

If you have the 160 remap (Recommended) then initialy you may find a drop in economy as you explore the new found performance.

But when that wears off and you return to normal the MPG will settle down,and the only way to test it is a Brim to Brim test.

Having said all that My MPG is on average 52 MPG and this is with a 160 re map and over many thousands of miles of different types of roads ect.And doing a Brim to Brim test.

We have one of each too, and I get the same difference when driving them - around 50 and 38 respectively.

I thought the auto would have been better cruising on long uninterrupted motorway runs when the autobox torque converter is locked up, but the best I ever got was 44 mpg.

Even with TC lockup, the engine still has to drive the hydraulic pump which powers the transmission. Also until the torque converter does lock up (which may depend on being in certain gears, above certain speeds or even above certain temperature), there's always some amount of slippage in it, which only happens in a manual when you change gear or are pulling away from standstill. Finally, I don't know if the auto 'boxes are four or five speed, but if four then the fewer ratios will be more of a compromise.

Autos are great for stop/start traffic and smooth rides, but you pay for this at the pumps. Remapping will make the car more enjoyable to drive, but it won't alter the pre-programmed rules for when to change gear and lock up the TC so you'll see less (economy) benefit than a driver of a manual who can take advantage of the extra power by upshifting earlier.

I'd be happy with 44mpg from an auto tourer, but changes in driving style may be able to improve on this- Google hypermiling for hints.

Are you just stating what the on board computer is telling you ? is so, do brim to brim tests.