johnr9q

Does anyone know the theory behind the operation of the stock MPG overhead monitor in my 99 Dodge Diesel?

phox_mulder

Little man with a calculator?


How bout this:

Computer is getting data from the injection pump, perhaps pump rotations (since it is a rotary pump) and data from the odometer.
It knows that one pump rotation is so much fuel, how much I have no idea.
It then takes the fuel flow numbers and distance traveled, plugs this into a "standard" and computes your MPG from this.

I know coming down a freeway offramp at 50+, engine at idle speed, the MPG jumps up to 99, which I assume is as high as it will go, then stays there till the speed starts dropping down around 20ish.

This is all speculation, gestimates if you will.


phox

dodgediesel4x4

Sounds like a good theory to me. Keep'em coming phox!

GlennRMK

I don't think its that complicated.

I would assume its just going off the fuel sending unit as approximately how much how fuel has been used in so many miles. Then computing it out.

That would explain why its not that accurate.