CO2 emissions petrol cars - reprogramming?

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Tue 8 Apr 2008 09:52
CO2 emissions petrol cars - reprogramming? - Optimist
Two things I've read recently have struck me.

1) Manufacturers compete with one another to program the ECU so that emissions in one car are slightly less than in a competitor's.

2) A Dodge, I think, with CVT is programmed in such a way as to give engine braking.

If it is possible to re-program to reduce emissions what do you lose elsewhere?

HJ is always saying don't engine brake because pads are cheaper than gearbox and clutch parts. So if you program an auto box to engine brake does that put emissions up to say nothing of wearing the box?

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Tue 8 Apr 2008 21:59
CO2 emissions petrol cars - reprogramming? - cjehuk
What you lose is often performance basically. On the "official" cycle the most you ever use is a tiny fraction of the average ~140Hp engine's output. Accelerations are slow by the standards of traffic on the real roads with plenty of smooth application and early changes. So program the ECU so that at light throttle openings and gentle accelerations and you get nice low fuel consumption/emissions, often just low enough to creep into a lower tax bracket. When a driver in the real world goes from a light opening to a wide throttle opening there is likely to be a little more lag than if these measures were not in place, equally a light throttle driver is rewarded by them though.

Having the auto box or even a manual box doing the braking does nothing to the emissions as when the engine is being driven by the road most modern ECUs cut off fuel to the engine completely having it work as a huge air compressor. While brake pads are cheaper than gears and clutches and I would not advocate changing down solely for the purpose of braking, there is much to be said for anticipating a long way in advance and coasting down with a gentle 6th to 3rd drop at an appropriate speed ready to pull away without having wasted energy braking.
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Tue 8 Apr 2008 22:06
CO2 emissions petrol cars - reprogramming? - Hamsafar
If the auto is programmed to engine brake by downshifting it will have a higher mpg because you slow down quicker, therefore, have to lift of the throttle later. My current VW is like this, with my old car, I could coast for ages gradually slowing down as there was a freewheeling clutch in the autobox. The VW makes horrible unwanted downshifts when coating and has a disappointing mpg commensurate with this.
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