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Worst Mechanic You Know
 
Gawernator's Avatar
 
Join Date: Apr 2012
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The 944 MPG Gauge

How accurate is the MPG gauge for you guys? I haven't yet fixed my odometer so I don't really know for sure.
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Old 09-09-2012, 09:38 PM
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Ornery Bastard
 
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It's reasonably accurate, but a lot of people don't understand how it works.

The gauge gets a signal based off of two readings: the injector duty cycle and the speedometer signal.

Below a certain speed (I think about 10 MPH), the gauge reads gallons per hour (the light grey scale that can be difficult to see). Only above that speed does it read in miles per gallon. A lot of people think that the gauge is broken because they don't see the second gallons per hour scale and think the gauge is reading something like 40 MPG at idle, when the gauge is actually reading 0.5 gallons per hour (the light grey scale).

On early cars (and the 924S), the gauge gets its speed signal from a hall-effect sensor on the speedometer itself. Failure of the hall-effect sensor will cause the MPG gauge to read in gallons/hour all the time because it will think the car isn't moving and so will stay in gallons/hour mode.

Basically, it's essentially as accurate as the digital mpg gauges in more modern cars, which is to say close enough for most purposes.
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Old 09-09-2012, 10:31 PM
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It does seem to move correctly with driving conditions, going up and downhill etc..

I'm getting quite good gas mileage then..
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Old 09-09-2012, 10:55 PM
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CASIS system - yes, it's pretty accurate on all the 944s I've owned.
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Old 09-10-2012, 09:53 AM
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I know that I went from 18 mpg to 23 mpg when I started to watch it closely as I drove to and from work. The upshift light as well. I still drive it like I stole it on occasion, but for the commute I now try to watch the gauge to squeeze out a few mpg's.

Also I am not in a big hurry to get to work.


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Originally Posted by Gawernator View Post
How accurate is the MPG gauge for you guys? I haven't yet fixed my odometer so I don't really know for sure.
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Old 09-10-2012, 03:57 PM
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i know i got 30-35 regularly on highways. although i never actually compared it against actual pump calculations...
Old 09-10-2012, 04:05 PM
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I generally shift early around ~2k RPM when the CASIS light comes on (with smooth gentle driving), I asked because on this highway where the limit is 55, the gauge says I am getting between 35-40 MPG and it seemed too good to be true.
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Old 09-10-2012, 05:28 PM
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Old 09-10-2012, 05:28 PM
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