MPG meter, reversing light switch.

Hi all,

 I found a multiplug disconnected from my gearbox, i reconnected it and magically my MPG meter started to work, even the MPG average seemed reasonable. After a few miles i was confronted with 99.9MPG on menu 1 and 99.9MPG on menu 2 and a MPG guage which was reading in every gear, i was under the impression it should only work in 5th. My reversing lights are stuck on too.

  So, waffle aside i assume the switch is bust and it thinks it's in 5th all the time. New switch is ordered so should cure it, am i being unreasonable to think that one day i could have a fully working and reasonably accurate MPG meter? and does anyone have an idea as to why i was getting a reasonable MPG figure but then it went up to 99.9 for the remainder of the journey?

  Thanks,

     Rob.

I don't think the speedo sensor in the gearbox has any impact on the MPG not working.

Is your cable operated speedo still working? - The MPG readings on the MFA are calculated engine vacuum AFAIK.

Hi,

 Yes, the speedo and tacho are both working. Its not the speedo sensor which i reconnected, as far as i'm aware, the mpg needle will only register when the gearbox is in 5th and this is controlled via a switch which is integral, or at least piggybacks onto the reversing light switch. The multiplug which connects to these switches was disconnected by a previous owner, obviously as an attempt to stop the reversing light operating all the time, instead of replacing the duff switch. The vacuum pipe has been connected all the time i've owned the car, althougb it needs this for the MPG gauge to work, it also needs an input from the gearbox. At least this is how i understand it!

  Cheers,
  
    Rob.

do the distance travelled and avg speed settings work ok?

the gauge up top i believe only works in 5th but the one in the digital display will work all the time (i assume because the digital computer gets a speed signal from the cluster, but analogue gauge does not)

the shift light is controlled by the vacuum switch inline with the vac line to the dizzy, and both mpg gauges use a vac signal from the engine so check the hose is intact and connected round the back. if that all checks out then i would say the vac sensor on the clocks is broken or the pcb is at fault somewhere

Weirdly on the upshift between 4th and 5th, but not actually in 4th or 5th, i get a breif, faint glow from the econo light. The MPG needle does work in 5th only which is correct, it is incredibly optimistic though! when i first set off, the digital MPG readout on pos 1 and pos 2 (selector switch) are about spot on but both readings steadilly climb until they both reach 99.9. I'm going to check the integrity of that vaccuum hose at the weekend and remove the instrument binnicle, see what happens. I can't comment on average speed, i've not checked it recently but as of a few weeks back it was reading similar to my beemer on the same journey.

 We'll get there eventually!

   Rob.

sounds like your switch needsa strip down and clean, you sometimes see new genuine ones on ebay though i think there is more than 1 type which is helpful!

Which switch? I've already stripped the multiplug type switch off the gearbox and that's now working fine, the 2 position selector switch also works, on pos 1 i get a different reading to pos 2 but after a while both readings, although slightly different for most of the time, eventually hit 99.9 and stay there.

  Cheers,

   Rob.

sorry i meant the reverse switch, if thats working then all good. maybe the vac switch on the dizzy line needs looking at if the upshift light still doesnt work?

Hi

  i have a small clear nylon tube which goes from the instrument cluster to the inlet manifold, this operates the mpg needle, i had no idea there was one going to the dizzy too, i hope this is the baby!

  Cheers  


   Rob.

yeah it comes from one of the nipples on the brake servo hose, this does the dizzy vacuum advance, the shift light vacuum switch is inline with it

I never knew some mk1 clusters also had a mpg needle as well as the MFA digital view!
Interesting… Got any pictures?