I have an 84 944 n/a. I also have the mpg gauge. What do these work off of?? Mine sways back and forth when driving-even at steady speeds. Is this off of vacuum or electrical? haow can I fix this problem? Also my "upshift" light does not work anymore- whats this hooked to? I would like to fix them but dont know where to start-HELP???!!!
Thanks,
John in NW Penna

 

The mpg is a purely electronic gauge, driven directly off the DME, and is dependent on the injector duty cycle (how often the injecotrs open). It's normal for this gauge to be somewhat jumpy, if it's excessive, most likely the gauge itself is at fault.

Ditto for the upshift light, most problems happen inside the tach. Sounds like an old wornout tach to me, you can get a used/rebuilt one through partsheaven.
Ahmet

 

Has the MPG gauge ever been stable? I had a digital dash on my 86 Taurus and the miles per gallon display (or the miles to empty for that matter) would jump around radically depending on the load on the engine. I think the computer is correcting itself so often that it cannot really give you an exact number, but rather a guestimation.

You may be driving at a steady speed, but the engine may be under a slightly different load from second to second, which could cause the results you are getting.

 

Mine's pretty stable if the load on the engine is not changing (ie: cruizing on a level road at constant speed).
Ahmet