Milage reader?

I have a 97 Xj with a over head console that tells me how many miles per gallon i get. How does it figure that? From the speedo gear in my t-case?
Is it accurate?
I know the best way is just to do the math on the trip meter but id still like to know where it gets its info from.:confused1

JEEPTUBE said:

I have a 97 Xj with a over head console that tells me how many miles per gallon i get. How does it figure that? From the speedo gear in my t-case?
Is it accurate?
I know the best way is just to do the math on the trip meter but id still like to know where it gets its info from.:confused1

Click to expand...

The PCM (Power Control Module)knows everything it needs to know to make this calculation.

On a 97' the odometer is run off an electronic pickup on the t-case output and fed to the PCM. The PCM then checks a lookup table and does some quick math based on the assumption that you are using stock tires. Based on that information, it can calculate distance, speed and acceleration.
It only displays 2 of those, distance and speed.
The PCM also knows how much fuel it is sending to the engine as it regulates that.

So, it knows distance, and it knows fuel volume. All it needs to know to do the calulation, right?

Cool, so the PCM knows all!!I wonder if it would make difference if it knew my tire size?
I must tell it.

JEEPTUBE said:

From the speedo gear in my t-case? Is it accurate?

Click to expand...

That's part of the information it uses. If the speedometer is inaccurate then the gas mileage calculations will be equally inaccurate.