mundo

By the DIC I'm sure average MPG is the average of instant MPG readings summed together over N samples. How are they calculating instant MPG? What could the algorithm be. It appears the TPS is involved but after resetting the average MPG display it goes down at an idle. No TPS involved at an idle. By the DIC I've seen average MPG get better in 5th gear rather than 6th. Without raising the revs in 6th on an a slight grade I've seen the MPG decrease with out throttle increase.

Any insight?

Mrc100

Velocity (distance/speed) / Rate of realtime fuel consumption calculated via realtime then extrapolated to miles per hour assuming continuous rates. That is why when you let off the gas and decelerate mpg decreases.

torquetube

It won't have anything to do with the throttle position. The DIC must get the fuel consumption data from the engine management system, which knows precisely how much gas is going into the engine because, well, that's what it controls.

The instantaneous fuel consumption is proportional to the injector pulse width, fuel pressure and manifold pressure.

Thrill6

MPG is Miles PER Gallon = Distance in Miles / Fuel in Gallons.

Velocity is a synonym for speed, which has nothing to do with calculating fuel economy. The reason the instanteous MPG goes up when you let up off the gas is because the engine is using less fuel, not because the car is going slower.

Mike V.

The more you press the pedal and the closer to the floor = worse MPG.

Ursoboostd

My guess is the DIC uses the pulse width of the injectors duty cycle and the size of the injectors in an equation.

Mrc100

When you're at idle and the car is slowing your instant mpg will decrease because you are covering less distance per unit of fuel consumed. Try it. I was answering the OP "Without raising the revs in 6th on an a slight grade I've seen the MPG decrease with out throttle increase.". The DIC uses velocity to calculate how much distance will be covered at the current rate of full consumption to calc eventual MPG figures. Likewise if the car is at idle and going downhill it instant mpg increases same fuel consumption but the car continues at the same speed or faster. This is a bit of simplification but essentially how it works.

coryvte

Its a wonder how some people can hold a job, let alone own a vette.

RnLi

You only need the basic math method or the DIC. Unless you are not revealing an ulterior motive

JIMSC62006

This was my thinking, too.

JIMSC62006

Why are you trying to make this so hard? Reset trip when filling up next time. Drive car for a certain amount of miles. Refuel car. Divide miles driven by gallons used=mpg.

This is not rocket science. It is 4th grade math.

Easy Rhino

RTQ - ATQ (Read the question - answer the question)

You answered a different question than was asked, that's why you are confounded.

1fastbob

I would use an abacus to calculate fuel mileage. Make sure it is not missing any *****.

Bob



http://en.wikipedia.org/wiki/Abacus

Mez

Both are are available in the PCM.

Throttle position won't be accurate in the calculation since the amount of fuel injected at low RPM is less than high RPM at full throttle.

Top_Fuel

My daily driver is a 2009 Pontiac G5 XFE. I've monitored every drop of fuel put into this thing for the last 30,000 miles. I calculate my own fuel mileage at every fill-up, and then log what the DIC has calculated for the same period. The DIC mileage is consistently within 2.5% of the mpg I calculate. So whatever algorithm GM is using, it's pretty good!

I do notice that the DIC mpg is always slightly more than the actual fuel economy.

mundo

That was my point. The DIC always shows a better average MPG then the good old calculation of miles / gallons used. If the DIC says 22 mpg the hand calculation will be about 21 mpg. So once again does anyone know the actual algorithm the ECM uses?

Migs08

http://lmgtfy.com/?q=instantaneous+fuel+economy

Batman 357

I've noticed the same thing in both my GM vehicles. The computer's milage figures are always better than actual milage. I wonder if that's by design or just as close as they can get the numbers. With all the computer equipment on the car I would think it would know exactly how much fuel was consumed and how far the vehicle had traveled.

Mez

2% should be within the margin of error.

Remember...there are a number of things that affect the fuel volume being injected. The PCM has tables for the lbs/minute rating for injectors, voltage offset to correct the fuel rate depending on system voltage and the fuel rate correction depending on the MAP (Manifold absolute pressure). Probably more corrections but you get the point. I am actually surprised its this close.

I wounder if the evap system is part of the calculation?

Gman in NC

We have this same system in our Equinox Sport as well as our C6. I compare them to my estimates with a calculator a lot. I've noticed the Equinox is off by maybe a mile or two per gallon and the Vette always seems to be within a tenth. It's been very close all the time.