If an aftermarket tuner(Banks) is installed on a truck. Why does the computer generated mpg say higher than it truly (hand calculated) is?

What is that computer truly computing to get those mpg's???

 

The PCM also calculates an MFDES, (mass fuel desired each stroke) off of pedal position and other various sensors. It converts this MFDES into a VFDES, (Volume of fuel desired each stroke) which is the amount of cubic millimeters of fuel delivered to each cylinder on each firing event (found my multiplying the MFDES by an estimated fuel density). By keeping a counter of firing events off of the CKP and CMP sensors, the computer knows how many firing events have been completed, and calculates a total of how many total mm^3 of fuel have been delivered. This calculation is converted from mm^3 (which a cubic millimeter is .001 milliliters) to imperical gallons, and the milage traveled in the given distance is divided by this to come up with the estimated MPG.

The reason yours always reads high is because your actual VFDES is much higher than the commanded VFDES from the PCM, thanks to the Banks unit intercepting it and raising it before it reaches the FICM on the valve cover to allow more fuel delivery- therefore more fuel is actually being delivered to the cylinder than the PCM is aware of.

The PCM knows the capacity of the tank, and the percentage fuel that is read by the tank sending unit, and calculates how much volume of fuel is left in the tank, and multiplies this by its estimated fuel economy value to get your "Miles to Empty" estimation read by the overhead meter.

The reason it is not always accurate is because it is impossible to get an EXACT fuel delivery calculation. Alot of people gripe and complain (on stock trucks) about the accuracy of the gauge, but considering how it must be calculated, I think it does a very fine job. When you calculate by hand, you are making a single calculation and a small percentage error poses very little threat to an accurate figure. However, seeing that the computer recalculates on every single firing cycle, it has ALOT of chances to be off a very minute amount. As you can imagine, a very, very small error multipled thousands and thousands of times can total up to a pretty significant amount. I highly doubt any human being could make that many thousand hand calculations and come out as accurately as it does, so people shouldn't rag it so hard

 

PSD 60L Fx4,

Wow great explination

The things that can be learned around here are amazing.

 

This horse is dead. Time for a new name. Einstein-o-meter? LOL! Mines been off my .05 MPG at most.

 

The best that has ever been here
Great to see ya my friend.

 

Right on man. Thanks for the break down!!!!

 

yes great explanation....all i know is that i have had mine down to 1 km b 4 empty yes that is pushing it...but all went well

 

A few simple changes could actually make this calculator useful.

For starters, MPG is significantly different while towing. Keeping track of two averages, one in Tow/Haul mode and one out. The DTE calculation could take this into consideration.

Alternatively, the DTE calculation could be based on the current MPG since last reset, rather than on a useless average. At least you could have some control over the DTE calculation based on your current driving conditions.

 

[QUOTE=RVRoadie] Keeping track of two averages, one in Tow/Haul mode and one out. The DTE calculation could take this into consideration.
QUOTE]

You know I don't think I've ever had it in Tow/Haul mode as long as I've had it, and I usually am hauling something atleast once a week, be it the flatbed gooseneck trailer or the 4-horse trailer. I don't think I've ever had a problem with the tranny(yet anyway). As far as I can tell, it hauls pretty good without the Tow/Haul setting, but the only mountains that I deal with(or foothills rather) are in Tn. and the few hills around Beorne and Fredericksburg back home in Tx., so I've never really had to gear it low for pulling. Most I've lost, MPG wise, in hauling is round .2 to .3 on the mileage. Now I don't have time to do the hand calcs and besides that I just used the computer's calcs as a guideline, nothing more.

 

What was the question . . . MPG OR Miles to Empty . . .

 

I am linking this thread in the 6.0 Tech Folder.

Thanks again, Matt.

 

Tell them Uncle Ted, and that feeling is coming over me again up here in the Great State of Michigan. Crimson Red Arrows and Back straps in the freezer! Don't you just love it.