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[wombatcurry]

Trying to diagnose a rough idle problem - I suspect that it's linked to the fact that the display consistently gives a reading of fuel consumption in the region of 40% lower than actual.
I know that these displays can be accurate (my old Omega is accurate to within 2-3 liters on a tankfull).
I know that the display takes its data from the computer.

Does anyone know how the computer calculates this figure (ie what data does it use from where)?

Thanks

[TheBoy]

Consumption is calculated from injector pulse length, as given by engine ecu, and speed signal from ABS unit.  It does some calculations dependant on engine, tyres etc, hence why MID has to be correctly programmed to your car type...

[wombatcurry]

Thanks for the info [smiley=dankk2.gif]

What generates the injector pulse length? (the ECU?)

[TheBoy]

Thanks for the info [smiley=dankk2.gif]

What generates the injector pulse length? (the ECU?)

yes

[wombatcurry]

Oops  

- what I really meant to ask is - what info does the ecu use to generate the injector pulse lengths? (I'm beginning to wonder if it is some faulty sensor creating my problem)
Thanks, Ian

[TheBoy]

Oops  

- what I really meant to ask is - what info does the ecu use to generate the injector pulse lengths? (I'm beginning to wonder if it is some faulty sensor creating my problem)
Thanks, Ian

All sensors.  Any that are faulty have substitute values, and on proper cars light up eml.  This being BMW junk means the eml doesn't come on when sensors fail  

[wombatcurry]

I wasn't aware of that....

I do have a fault code 96 (egr valve), but having stripped it down & cleaned it this weekend couldn't find anything wrong (except for the usual tons of black goo in the inlet - yeuch). You don't know if there's a feedback from the egr solenoid to the ecu by any chance?

[TheBoy]

I wasn't aware of that....

I do have a fault code 96 (egr valve), but having stripped it down & cleaned it this weekend couldn't find anything wrong (except for the usual tons of black goo in the inlet - yeuch). You don't know if there's a feedback from the egr solenoid to the ecu by any chance?

No direct feedback, but an implied one via other means...