MPG ECM dash or peoplenet how is it calculated

Only accurate mpg calculation is fuel purchased divided by miles ran anything else is only an estimate

 

I agree. The GPS is only a estimate and is a loose one at that. It's good to less than 50 feet on the Planet by order of President Clinton sometime after 1996 so that the Civilians, that's you and me who happen to have access to the early GPS units know that somewhere in a circle of 50 feet here we are on the surface of the planet.

Much much much more accurage down to the millimeter is reserved for the Military for war fighting. They will know exactly how far from point A of anything in the sky, ground, sea to point B anywhere in the earth, above it or under it.

You put fuel into your tanks. It comes up to a certain number of gallons to fill it.

You have the miles written down from your previous fillup and with a little paper math you will have your current miles per gallon to the tenth accuracy. Your ENGINE ECM will know exactly how much fuel has been burned over it's life time and how FAR it has been driven to the tenth of a mile over that same life time. The average it comes up with will be slightly different than what you came up with between fillups but no less accurate.

It also knows how many hours you put on a engine, And thence by defining the time burnt, you know your average gallons burned per hour. For trucking generally it's not something we think of. But for pilots who must account for the price of getting to say 14000 feet when it's 105 on the ground here in the middle of july, that much fuel might require a stop before you reach where you are going.)

Or in the case of my famous vermont 3 mile pull, I used approximately 45 gallons in a little over a hour and change to go three miles up a 25% at less than walking pace. I had 65 gallons in that one tank and losing most of it meant I now had to find fuel somewhere, even if it is at a convience store with my own cash until we got far enough south to a major truckstop that took fuel cards to fill it.

I used to maintain a rolling number of miles per gallon currently performing on my vehicles here at home. One in particular was dead consistant at 32 miles to gallon until it's time for a oil change then that number drops to 29 miles to gallon or so even though the exact amount of driving, speeds, places driven to etc that week has not changed from the week before etc. Once the oil change was done, the mileage goes right back up to 32 right where it's supposed to be the way we ran it.

That's just a example. It can also be used to audit your gas use to make sure that the 15 gallons or whtaever you bought into your tank is actually USED by the engine rather than stolen because you did not have a locking cap on your tank. We caught a thief who would only take two gallons at night twice a week. A game camera confirmed the thieft before we put both a locking cap on and turned in the video and his image to the local police. And that was the end of that.

If your tractor trailer suddenly demands fuel as in thirsty all the time, that means either you have had fuel stolen, or you ran over something and are dumping fuel all over the place as you go down the road or worse make a lake of spilled fuel under you while you sleep.

 

Engines don’t have flow meters and without one it’s just a guesstimate using a bunch of factors.. horsepower used idle speed etc etc.. over the years they are closer but still not accurate

 

miles driven/gallons to fill about the most accurate I know of.

 

Fuel guages is an app i use. Fill in mileage and gallons and it does the math for you. There is no other accurate way than paper and math.

 

The ECM of course uses ECM miles, which are never perfect, but close enough. The engine ECM knows flow rate of fuel based off injector on time, injection pressure, etc. Then there is a correction factor becasue injector flow is not instantly full flow/off and there is flow differences with different injection pressures vs. cylinder pressures. Add up all these factors and it's a close guess, not perfect. Plus engine manufactures each come up with their own algorithms.

The PeopleNet defaults to GPS, but you can change the odometer source to the data link. We did that because with car haulers, you often get a weak GPS signal when loaded. Also, using the data link miles always keeps the PeopleNet in sync with the trucks odometer. Even then, you still get discrepancies in miles per gallon between the truck and PeopleNet. These computers are not calculating MPG in true real time, only close to real time, they don't make infinite calculations on the fly. The computers must take many snap shots to calculator your current MPG. PeopleNet and Cummins both have their own idea of what the best rate is for taking these snap shots.

If you want to know how different sampling rates can change how it calculates MPG. Imagine slowing down the rate from several per second to once ever 100 seconds. If you're just cruising and every 100 seconds put your foot to the floor, then go back to just cruising. The ECM would calculate that as 100% of the time your at full throttle with a very high flow rate and very poor MPG. Driving style can also affect how accurate it is. I found that the way Detroit figures it is almost dead on and Cummins shows 4-5 tenths too high. A different driver may find the opposite becasue he drives different and the way Cummins figures it better suits his style.

The short story, if you want to know exact, measure it. If you want to use it to see trends up and down, it's a good tool for that.

 

Top secret magic.