How Ethanol Flex Kits and Sensors Work E85

[steve99]

How Ethanol Flex Kits and Sensors Work E85


E85 - supposedly 85% ethanol and 15% petrol, but content can vary in places from E50-E90 and between summer and winter blends

Flex Fuel - often interchanged with the word E85 but not really correct - Flex fuel is a flexable fuel tuned vehicle that can automatically cope with any combination of petrol and ethanol content fuels. Often E85 is the max as it get hard to start high ethanol content fuels in cold weather below 5C or 40F

Flex Kit - This is term often used to refer to the hardware components, flex fuel sensor, content analysier, fuel fittings and wiring harness required to convert a "petrol" car to flex fuel or E85 use. Note you also need a new tune so ECU can interpret the signal from the flex kit and act on it.

Flex Fuel Tune - This is the software/firmware changes required to be done to the ECU so it knows how to interpret the signal from the Flex Kit/sensor and adjust the fueling/timing/boost as ethanol content changes.

Ethanol Content Analysier ECA - electronic box that interprets flex sensor output of ethanol content and fuel temperature, converts to 0-5v DC signal fed to ECU and often provides dislay or Bluetooth output. as

Our cars were only tuned to run petrol or up to about 10% ethanol fuels.

However the fuel system components seem comparable with E85 fuels as we are not seeing a whole pile of issues and people been running E85 for 5 years.


If you had a consistent source of E85 fuel that was allways E85 or E70 or whatever you could just tune for that and you wold be fine.

On a Naturally Aspirated (NA) car their is enough adjustment in ECU to cope with about a 15% or so change in ethanol content so if you tune for about E70 you can safely run between about E60 and E90.

See here for more info NA Cars with dedicated E85 tunes, you can do this with any tune system
http://www.ft86club.com/forums/showthread.php?t=67310


On a Boosted car (turbo or Supercharger) you don't have that amount of tolerance for ethanol content so you definitly need a full Flex Fuel system unless you have a constant percent ethanol fuel source.

In USA the supposedly E85 fuel can vary now from about E50 to E90, such a wide variation can now be a problem for NA cars unless your fuel is always in a small variation range and you may have to re-tweak your tune a little to cope well with E content below about E65.


So Flex kits their are several components

Here is representation of where flex sensor fits , note our fuel system is different , just shows that the flex sensor is T'ed into the fuel line so it can sense fuel content and feed signal to ECU





Below is the insides of a Flex fuel sensor. It essentially a capacitor and is fed with a constant frequency signal. As the ethanol content changes the dielectric constant of the fuel changes and this pull the signal frequency from 50hz to 150hz.

So these sensors don't actually measure ethanol content they measure the dielectric constant of the fuel, and use this to determine Ethanol content The sensors are calibrated for a mix of petrol and ethanol only. So if your fuel contains other weird crap like water or other additives in sufficient quantities it will effect the sensor readings.








This signal is then converted by another electronic box the Ethanol Content analysier (ECA), into a 0 to 5V DC voltage.

This 0-5V DC voltage is then fed into the ECU either via the EVAP Pressure sensor input or the REAR 02 Sensor.





This signal is then converted by another electronic box the Ethanol Content analysier (ECA), into a 0 to 5V DC voltage.

This 0-5V DC voltage is then fed into the ECU either via the EVAP Pressure sensor input or the REAR 02 Sensor.








Further reading if your interested
https://cecas.clemson.edu/cvel/auto/...el-sensor.html




So three main bits in a flex kit are the flex fuel sensor, the Ethanol content Analysier (ECA) and usually a display. although some kits use a Bluetooth output to your phone/tablet etc instead of a display.


Now if you have your flex kit hardware installed ir fuel connection and electronics connected. you will now be feeding a 0-5v DC signal into your ECU. this will be via the EVAP Pressure sensor input or the REAR 02 Signal into ECU.

Now that going to confuse the hell out of the ECU with standard software (tune) installed in ECU, so you now need a flex fuel TUNE , to re purpose either the EVAP or rear or inputs on the ECU to be the 0-5v flex fuel signal.

The tune will know its no longer looking for a rear 02 sensor or evap pressure sensor and it will now use that signal to alter the fueling/timing and boost on your engine depending on the ethanol content

[VABeachBRZ]

Great write up!

[Shady195]

Awesome stuff as always Steve!

[Detroiter]

Great info Steve!

I'm thinking about attempting to make my own flex fuel tune for OFT and saw a thread about it a while back by the user who first developed it for OFT tunes I believe but I can't remember his user name. Also I can't seem to find it through any sort of google and search though. Would anyone be able to point me in the right direction? Thanks!

[elBarto]

Originally Posted by Detroiter

Great info Steve!

I'm thinking about attempting to make my own flex fuel tune for OFT and saw a thread about it a while back by the user who first developed it for OFT tunes I believe but I can't remember his user name. Also I can't seem to find it through any sort of google and search though. Would anyone be able to point me in the right direction? Thanks!

You are looking for "ztan" . That's the guy who made the flexfuel tune and also made a Speed density patch and a boost cut patch.

This is the topic you are looking for: Opensource flexfuel