Efficiency - MPG guage

Post here for mechanical and engine topics such as fuel issues, transmission problems, rough idle, exhaust, electrical issues, etc

Moderators: GRNSHRK, ron, bfons

Post Reply
sideshowbob
Posts: 247
Joined: Mon Aug 01, 2011 2:18 pm
Location: Hampshire UK

Efficiency - MPG guage

Post by sideshowbob »

Car is '89 635CSi Highline and have been using it to go to work over last few days. On my way home this evening I noticed that the fuel efficiency guage has started to play up or not as the case may be.

Noticed that it had swung over to the far right and was not responding at all to throttle position, engine revs etc.

So out of interest I pulled over selected neutral and turned engine off. No movement.

Turned engine back on and meter started to move but only in a very sluggish way. It was only a short distance to home so investigation was halted.

This begs the question how does this efficiency guage work. Where does it take its info. from and if faulty does it have any detrimental effects anywhere else ?

Thanks
User avatar
635sharknose
Posts: 513
Joined: Fri Sep 13, 2019 4:58 pm
Location: The Netherlands
Contact:

Re: Efficiency - MPG guage

Post by 635sharknose »

I did have issues with this gauge as well (jumping up and down). It was solved when I polished and cleaned all contacts with cleaning spray.
Paul
Image
Instagram: @635sharknose
1987 635CSi Bronzitbeige
Jubilados
Posts: 161
Joined: Sun Mar 08, 2020 4:48 am
Location: So Cal

Re: Efficiency - MPG guage

Post by Jubilados »

It is electronic and gets its info from the ECU.
One of the pins on the ECU (I think usually pin 11) sends the info to the gauge.
It not working won’t affect anything else, except maybe the MPG reading on the OBC.
plip1953
Posts: 400
Joined: Mon Aug 13, 2018 4:15 pm
Location: Leeds

Re: Efficiency - MPG guage

Post by plip1953 »

Out of interest, what info would the ecu need/receive specifically to supply a value for the gauge to display? Would roadspeed and injector activity info be sufficient? As far as the fuel consumption and range values displayed on the "computer" are concerned, I guess there needs to be more in the way of inputs eg current fuel level and stored info re past consumption rates?
Phil
__________________________

1988 Highline 635 CSi
Post Reply