Learning about engine control from OBD2 data

[orangeTomato]

After wondering why the shift indicator in my dashboard sometimes tells me to shift when the green/blueish/blue ecometer said I was being economical, I bought an cheapey ELM327 to try and understand why.

So here's some things that I learnt. It's probably basic stuff to any ECU designers out there.

1.3L engine, manual transmission, car is 5 years old with 32k miles. 9k miles since last oil change (!).

* My best guess is that the ecometer is mostly an "EGR-ometer", as in 6th gear it seems to turn blueish when the EGR valve shuts due to increased engine load.

* I'm guessing the shift inndicator is just advising about fuel economy, but I'd need to find a flat road on a calm day to fully confirm this.

* I haven't worked out what makes the ecometer turn fully blue in 6th gear as the load continues to climb -- maybe just some arbitrary bad threshold for emissions? Perhaps unable to keep cat within its ideal temperature range or something like that?

* Seems like the EGR knows how to open gradually under increasing load, but at a certain point it just slams shut (hard transition to some other control scheme?). I'm surprised that the car can do this without a change in feel.

* Looks like several of the generic OBD params are "heavily processed" or completely modelled. For example the catalytic converter temperature resets to 21 if the engine is restarted.

* Similarly I assume that when the EGR valve is opened, the throttle valve must open (much?) wider to compensate for reduced manifold vacuum, but the OBD values don't show this.

* Although there seems to be a neutral detection sensor that's used by the start-stop, the cruise control doesn't seem to use it. If I'm on the right gradient I can pop into neutral and the cruise control sometimes holds the revs steady (Assume the same cruise control funciton doesn't need to care about such a sensor, so it doesn't).

* A slight throttle remap gets applied when AC is on. So if you need to feel a bit better after your AC fails (or want to disctract a buyer), you could relabel it as the "sport button"

[Marco1979]

You made a real study of this; impressed! Personally I think the blue/green indication is very much simplified and depends e.g. on throttle position. A slight pressure on the throttle seems economical, but wide open throttle and a few seconds later an upshift might be more economical in reality. On ecomodder.com I read that you should keep revs low, throttle wide open, and at cruising speed either use pulse and glide or very gently apply the throttle to maintain in Atkinson mode.
You might want to include the instant fuel consumption as this indicates the ‘end result’ of all parameters involved.

[Downsizer]

I found the green/blue “economy” indicator was no help to me, so I disabled it. As my car is cvt I just let the car do what it wants with the ratios.

[Jocko]

I just use the Instant mpg. My Mk 1 didn't have an Ecomometer but I fitted a ScanGaugeE and found the Instant mpg a brilliant tool, especially for indicating Deceleration Fuel Cut Off operation. With the Fabia, I have an Instant mpg display so I no longer use the ScanGauge.

[TnTkr]

I suppose you could see throttle position from OBD signals and found out that the changing lights follows throttle position on 6th gear. In lower gears it evetually turns blue unless you lift off the throttle completely.