Apparent Small Bug in Prius MFD Instantaneous FE dispay

I see this sometimes in the morning on my way to work. When I'm doing 50mph before the car has warmed up and in stage 2 I think, I will try to do a high speed glide. What I get is no arrows and 99mpg on the MFD. This looks just like a low speed glide except the engine is still spinning and burning .1 gallons per hour and its somewhere in the 30-40mpg according to my Can-View.

 

My SuperMID M-1 measures the fuel injector pulse width, and it clearly shows zero msec injector ON period on highway coasting.

Ken@Japan
PRIUS DIY

 

There is no injector pulse width data on the CAN message, I believe.
I think Prius MFD data is using the injector pulse width for the instantaneous mpg display same as my SuperMID.

I'm trying to read the graphcan.c source code of Mycanscan project, but I could not find how they calc the instantaneous mpg yet.

Ken@Japan

 

One thing that I learned, early on, was that the MFD lies.

 

Try this: let the engine idle in neutral while coasting down
from 30 mph or so, and watch the iFCD. Around 18 MPH it
starts to float down a little from 99.9 and still likely
registers a reasonably accurate figure -- if you could
stay in a low idle with a 1.6 ms injector time while being
magically pushed around at normal speeds, you probably
*would* get over 99.9 MPG regardless.
.
_H*

 

I had a similar problem with my Graham scanner but it turns out the two fuel consumption values do not go to "zero" but just a low number: (1) injector timing, and (2) mass air flow. I had to adjust my spreadsheet to treat these 'low values' as zero and then there was agreement.

Bob Wilson

 

The Graham scanner doesn't calculate or display mileage but it does report two metrics that give can give fuel consumption, mass air flow as well as injector timing. Originally proposed by Florian Steiper, the mass air flow is in a 14.7 to 1 air to fuel ratio. Injector timing and engine rpm can also provide the fuel consumed. Given the Graham scanner only reports up to six variables, it is important to choose which is used carefully but both will not go to "zero" but rather a low value that has to be treated as zero.

Ken@Japan first pointed out that direct injector timing monitoring is a much better metric than OBD reported injector timing. I've figured out it is because they don't 'return to zero' but a low value that should be treated as zero.

Bob Wilson

 

OK, following is what I read from the program source.
The data came from CAN-ID:0x348, throttle related number, stated by Attila's spreadsheet.
If engine rpm=0, then the value is forced to zero, else the value is used.
The throttle value is converted to mpg number using following formula.

MPG = (float) ((SpeedV * (float) SPDSCALER_MILE) / ThrottleV);

My bet is Mycanscan has the bug, and Prius MFD and my SuperMID show the fuel-cut correctly.

Ken@Japan

 

i posted this about 2 years ago... happens when coasting downhill before engine is warm. i can hear engine running, but no indication on MFD of that. apparently does not show up when in warmup mode...definitely a bit weird.