Physical ethanol sensor speed?

[Marky Dissod]

Just guessing here but i would think that it would take a little but of time / few miles or so driving before the sensor could pick out the exact mixture given that the fuel that it’s trying to read is a liquid that’s already diluted with other grades of fuel in the tank.

It’s not like it’s trying to determine a total amount of fuel in the tank like how a float gauge would give,
it’s a specific amount of a grade of fuel it’s trying to determine.
I don’t think the reading would be instantaneous like an 02 sensor.

But this could be totally wrong, i almost feel bad posting this skimming thru some of the more knowledgeable replies.

It likely deduces the ethanol concentration after being given enough time.
It notices an O2 voltage, and makes an adjustment.
Before, when the pcm knew exactly what kind of fuel it was working with,
it understood exactly the magnitude of the effect it would have by making X amount of an adjustment.

But since it doesn't know the ethanol concentration of the fuel it's working with -
it only knows it recently refueled by more than 3 gallons, and that it should recalculate -
it eventually (re)learns the fuel that it's working with by making a fueling adjustment,
seeing how much that fueling adjustment affects things,
and the closer its adjustments meet its expectations, the better it knows what fuel it's working with.

 

[Fless]

From what I can tell, the physical sensors calculate the alcohol content using frequency, which jibes with the Tech 2 alcohol frequency info.

Megasquirt ECU: Flex Fuel Sensor

If you’re looking to run E85 but not willing to commit to using it as your only fuel, adding a flex sensor is a great solution that allows you to run anywhere between 0% ethanol and 100% etha…

bartuneengineering.wordpress.com

 

[j91z28d1]

From what I can tell, the physical sensors calculate the alcohol content using frequency, which jibes with the Tech 2 alcohol frequency info.

Megasquirt ECU: Flex Fuel Sensor

If you’re looking to run E85 but not willing to commit to using it as your only fuel, adding a flex sensor is a great solution that allows you to run anywhere between 0% ethanol and 100% etha…

bartuneengineering.wordpress.com

Yes the physical sensor is in the fuel flow, it then outputs a pwm frequency to tell the ecm how much e it has. the ecm will then use it to blend the e tables and gas tables together based on that precent.

I'm pretty sure the lag you're seeing is not in the sensor output itself. other than the time it takes the fuel to mix and make it to the the sensor.

 

[kbuskill]

being you were idling with the fuel cap off, you might have just introduce a vac leak thru the evap system changing the fuel trims. in the same way pulling the clean side air intake tube to valve cover will change trims quickly.


also if you have newer non return style fuel system. I can idle for a decent amount of time on the fuel in the rail and lines. I don't believe I've read about much lag in the sensor itself, but there will be filter settings in the ecm code. there is for almost all inputs, hpt just doesn't define everything, either because it's not normally needed to tune, or not worth the work unless requested.

I could maybe see the vacuum leak theory if the purge solenoid opened while refueling but even then it would still be pulling air through all the fuel vapors in the tank,which would be alot especially while pumping gas into the tank.

 

[hagar]

I personally think PPV nailed it with the blend time. I run a pump out splitter on e85 cars that switch between gas and e85. When i pump the gas out to nothing, then fill the tank with e85, it registers the full ratio of the e85 as soon as I turn the key back on, no delay. Haven't tried doing it without turning the key off so maybe there is something to that as well. To answer your original question though, for me, sensor instantly report back the change.