trip computer, mpg

[Matteh]

I was just wondering how the mk2 trip computer calculates current mpg etc..?

obviously it needs to know speed and fuel usage.

speed is obtained via the speed sensor in the gearbox (for a ph1) and is fed into the ecu. how is it then transmitted to the dash?

I guess the fuel consumption figure comes from the ecu too (or is there a fuel flow meter somewhere?) - again, how does this info get to the dash if its from the ecu. I can't find any mention of these in the ecu pin data diagram:

http://i189.photobucket.com/albums/z18/Matteh449/F4R/172ECU.jpg

or is it obtained via the diagnostic? :quiet:

 

[bmh.01]

The ecu can meter fuel knowing the fuel rail pressure and injector flow rating then how long its pulsing the injectors for, think it uses canbus for the data transfer or the Ph2 does at least.

 

[Matteh]

how does the data get from the ecu to the dash?

 

[bmh.01]

As I said above on the Ph2 it goes over the canbus network, believe the ph1 172 does the same. Guessing your looking to get it working? Won't worth without a uch in the mix I believe.

 

[Matteh]

i think I have zero chance of getting a mk2 trip computer to work

I was just curious as to how the information gets to the dash, given that the ecu only seems to be connected to obd (not canbus).

I had noticed the R19 trip computers do similar functions, but again need a fuel consumption input. it seem they need a pulse for every 8 (or 80?) mm^3 of fuel fired - not sure if this is equivilant to 1 batch injector pulse. if it were that simple it'd be pish to wire up - but it never is

 

[bmh.01]

Don't think it is with the Ph1 172 but then again i'm not 100% sure on ph1 wiring.

 

[micallef1990]

does anyone know why mine doesnt work i press the button and it doesnt change from current mileage