Highly Inaccurate DIC

[jgooch1548]

Wow that's a weird title...

I have an issue with user Displayed info with the DIC on two of my customers LBZ's that I have recently done DSP5 with economy tuning in them.
Both users are showing about 30.0mpg on the highway and were really excited but I had to burst their bubbles and make them manually calculate the mileage and they are about 21 mpg on the highway. The tunes were pretty much identical other than requested Pedal responses. They both have 26gal tanks and when they fill up the pump tells them they put in about 21gal of fuel but DIC shows they only used 12 to 13gal of fuel (hence the false readings). Now both of them have other tunes that are more accurate (not completely but a lot closer).

Does anyone have any idea to something that I may have messed up or fat fingered?

[SASDakota]

In the interest of self diagnosis did you log all the usual PIDs when tuning for mileage and compare each tune to current revision to see how the ECU reacted to each tune?

[jgooch1548]

To a certain extent. One is my dads LBZ so hopefully I can borrow his for a day and play with it to see if I can catch anything.

Going back over my edit history in the non DSP5 tunes from my dads before I moved them all, I don't see anything that I changed on one that I didn't change on the other. Especially in the area of fuel calculations.

[Chavez91]

Basically any changes you make to pulse width, fuel pressure, ect. are going to effect its accuracy in the areas adjusted as the DIC tables are calibrated for the volume of fuel being used in a stock tune. For example a modded tune,if there is more fuel down low in the new tune, it needs less MM3 to cruise therefore according to the calculations using the DIC table, the ecm thinks its using alot less fuel to go just as fast, when it really isnt.

[jgooch1548]

Thanks Josh. Sometimes you get wrapped up and over think the logical and simple thoughts.

[THEFERMANATOR]

It's to be expected when you tune one. The DIC fuel used is calculated via teh BCm from 06 on, so it's not like 03-05 where you could recalibrate the table for fuel used to make the DIC correct again. Sounds like your economy tune though is set up to fuel very quickly though as all of my econ tunes read just a few MPG high.