Torque and Lexus onboard computer MPG

[jasonck08]

So I just bought a 1999 RX300 with 100K miles. Not even driven 200 miles yet on it...

Also just bought an OBDII BT transmitter and Torque.

Whats really strange is that Torque consistently reports lower real time MPG than my cars computer (1-2MPG highway for example, and 10-20% when coasting). However the overall Torque average is much higher than what my cars computer says. 29MPG on Torque avg, vs 21.5 MPG on the cars computer.

Whats up with that?

Guess I'll have to wait to fill up the tank... Is there anyway to calibrate Torque. I went through the menu's and didn't see anything.

[Bergi85]

Originally Posted by jasonck08

However the overall Torque average is much higher than what my cars computer says. 29MPG on Torque avg, vs 21.5 MPG on the cars computer.

I have a 2000 RX300 as well. Are you averaging 21.5 mpg? That is pretty good! I average, according to the Lexus computer, 18mpg.

I am getting the bluetooth OBD2 scanner this week so I will hook mine up and see if I get the same results as you.

[mcrews]

I would think that there is an adjustment.

My understanding (very weak) is that obdII doesnt read the actual flow of gas. It's computing it off of data provided. Which would lead me to believe it has to be calibrated.
I know the scangauge had to be calibrated and it's reading obdII info.

I always verifiy the miles driven off of a gps garmin.
The scangauge alows for a calibration of distance driven.
as a note: always calibrate in metric. It allows for tighter calibration. Then switch back to miles.

[RobertISaar]

fuel economy calculations can be done quite a few different ways, instantaneous MPGs should always be fairly similar between all methods, but trip MPG is where things can get messed up.

the way most factory installations work is by accumulating the total amount of time the injectors are open, knowing the injector flowrate and knowing the distance traveled. distance traveled and injector on-time require accumulators, essentially they'll total up to "amount of fuel injected" and "distance traveled". in standard units, probably "gallons injected" and "miles traveled", after which only a single division operation will give you a MPG value.

the way a lot of aftermarket units calculate fuel economy is different... because OBD2 SAE requirements don't specify an accumulating injector ontime value to be available for streaming, they won't have that capability. instead, it has to be estimated knowing RPM and injector pulsewidth and a guess at injector flowrate. another method is using calculated airflow and target AFR to guess at fuel flow. neither of these methods work very well for trip numbers without significant tweaking.