mpg and 'learning' ECUs

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Tue 26 Sep 2006 08:26
mpg and 'learning' ECUs - Red Baron
The thread by Westpig got me thinking.

In modern ECUs, some of which are purported to be of the 'learning' type, how long does it take for fuel consumption to stabilize at the new driving style?

If my Mondeo TDCi 5-speed has such an ECU (correct me if I'm wrong), then I have this evidence:

If only I use the car for commuting for several tank-fulls, I will get just over 50 mpg. If my wife and I swap the car at about every tank-full, then my commute mpg drops to 47-ish. If my wife has sole use, then the mpg hovers at around 43mpg (6 x 1.5 - 2 mile journeys per day and the odd longer one).

This evidence would back up my theory.

Is it really the ECU trying to be clever or do the lumps of metal and plastic themselves simply take a while to settle to different usage regimes?
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Tue 26 Sep 2006 08:33
mpg and 'learning' ECUs - cheddar
The TDCi ECU is a "learning" I have been advised that it may be beneficial to disconnect the battery every now and then, every 10k or so, to clear the memory particularly if you buy a 2nd hand one and you dont know how it has been driven before. Not sure of the value of this though I know there are a number of people that reckon it makes a difference. if you do it the battery has to be disconnected for at least 30 mins and you will need to knw the radio code and how to reset the elec windows, the latter is easy and is described in the manual.
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Tue 26 Sep 2006 08:47
mpg and 'learning' ECUs - Collos25
Its the software that computes the MPG it has a lead and lag syndrome on the Mondeo although it shows a lower figure it is in all probability doing more I have noticed this on my Mondeo.I think they must calculate over a certain distance so although you are in a high mpg phase of driving it still has the lower phase in its memory.
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Tue 26 Sep 2006 10:17
mpg and 'learning' ECUs - cheddar
Its the software that computes the MPG ............. think they must calculate over a certain
distance so although you are in a high mpg phase
of driving it still has the lower phase in its memory.


That is a good point and relates to the trip comp function though is independant of the learning ECU which is to do with driving style, not all models have a trip comp afterall.
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Tue 26 Sep 2006 10:52
mpg and 'learning' ECUs - Red Baron
My mpg figures are brim-to-brim measurements as my 03 Zetec does not have a trip computer.

The ECU clearly has a limited memory and that eventually, data that it hold about driving style must either get deleted or fall off the bottom of the list.
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