dogger

Can anyone tell me why the MPG calculation from the overhead console is so far off with a fueling box? Mine will read 23+ mpg occasionally running down the highway empty but put it to paper it's 18.5 mpg. Have 15K on it now with a Diesel Dynamics True Torque module for the past 10K. Was much closer without the box.

I thought it would use at least the fuel guage and odometer for the calculation, if not a flowmeter in the fuel line and the odometer. My old '89 5.8 liter F-250 Supercab 4X4 5 speed manual does only 11.8 + a smidge under the same conditions, so
I not complaining, just wondering. .


L8r,..........dogger

Days on, sweatin' in the Sahara Desert!!!!!!!!!!!!!

The Boss Hog

dogger,
It is because of the way the computer computes the mileage. The ECM controls how much fuel to inject into the engine based on the inputs it gets from its sensors including the throttle position sensor. The fueling box modifies the output of some sensors which fools the ECM into thinking it is injecting less fuel than it really is. As an example, it tells the ECM that the fuel pressure is lower than it really is. At WOT this allows for more fuel to be actually injected (more power!) than would normally be the case (ie the ECM raises the fuel pressure up to what it thinks is its max but it is really higher than its normal max!). During cruise the ECM thinks it is using less fuel than it really is to maintain a specific speed therefore it computes better fuel mileage.

Simple, right . . . . . .

The Boss Hog
(that's my story and . . . . . . )

stevenknapp

Ya, that's the gist of it. There is no sensor that tells it fuel used, the ECU knows how much fuel it injects, and adds that up. This is based on fuel pressure and injection time.

When you start playing around with the system adding extra fuel without the ECU knowing the overhead gets confused.

skeeter

I cannot understand why you would do all those modes to a new truck . you have voided your warranty. i have the same truck 03 4x4 2500 4 door 6 speed 10k miles on truck
last week end we went to lake havasu. from flagstaff to kingman 21mpg.
from kingman to parker az for 3 days and back to kingman 18.5 from kingman to flagstaff up hill 19mpg all figured by hand not by over head I really love this truck

The Boss Hog

Old Navy saying #231: "Too much horsepower is not quite enough"

The Boss Hog
( . . . . . . . . )

moopa

Originally posted by skeeter
I cannot understand why you would do all those modes to a new truck . ...

I think it's a case of..."Because we can,and we will!" It's fun to play and experiment with our toys! Remember the old addage...you only live once,and you're dead the rest of the time.... Mark.

dogger

Wow! Really sophisticated method for simple calculation. Thanks for the information.

L8r,.............dogger

stevenknapp

Wow! Really sophisticated method for simple calculation. Thanks for the information.

Actually it's pretty simple compared to the other options. An accurate fuel flow sensor would add cost and be a potential point of failure.

The ECU is calculating how much fuel to inject as part of it's normal operation, that's one of it's primary functions. The MPG stuff just comes from keeping a running tab of that amount from injection event to injection event.