Flex Fuel

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Flex fuel is available for the KPro4 only when used with a PRB or PRA calibration


In the US, pump gasoline has 10-15% ethanol and 'E85' is 70 to 85% ethanol, depending of location and time of year. Flex fuel offers the ability to compensate for different fuel ethanol content by using an ethanol content, which is useful when switching from gasoline to ethanol (and vise verse) or when the E85 ethanol content is seasonally altered.


Digital Input

With the KPro4 an ethanol content sensor may be connected directly to the KPro using the Ethanol input.  No ethanol content analyzer is needed, as the KPro4 converts the signal from the ethanol content sensor directly.  Suitable sensors are GM part numbers 13577394, 13577379, and 13577429.  These sensors produce a pulse width modulated output with a variable frequency as well, which ranges from 50 Hz for 0% ethanol to 150Hz for 100% ethanol.




Part numbers:

Ethanol content sensor GM 13577429
Plug & pigtail GM 13352241
3/8" fuel line to -6 adapter Russell 644123 x 2


The sensor should be placed in the return line from the fuel rail to the fuel tank.


Sensor wiring:

'Vcc'  -  power (9-18V)
'Gnd' - ground
'Out' - output to ECU.


The KPro has a built in 2.4 k ohm pull up resistor on the ethanol input, so no additional resistor needs to be wired between Out and Vcc.




The ethanol sensor will only read ethanol content correctly with fuel flowing through it, so it should be placed in return line so that it gets constant flow past the sensor whilst the engine is running.  It also means that once the fuel pump stops the ethanol content will not read correctly.  eg if the ignition is switched on, but the engine not running.  Because of this the KPro does not send the ethanol information to the ECU unless the fuel pump is running.


The direction of fuel flow through the sensor is not important.




Ethanol content input enabled

Enables the ethanol content sensor input and compensation tables.


Smoothing time factor

Specifies the moving average time factor.  A small value will update the ethanol content quickly, and respond to changes quickly, whereas a large value will respond slowly.

A value of 1000 results in the ethanol content taking roughly 10 minutes for a full scale change.  A value of 10 will respond to sensor changes almost instantly.

The ethanol content is retained after the vehicle is switched off in order to correctly compensate when cranking.  If you have changed the ethanol content in the fuel tank, then the ethanol content will update after 10-15 seconds of engine running.


Maximum engine speed for update

This settings stops the KPro from reading from the ethanol sensor when the engine speed is over a certain value.  This is for fuel systems where the ethanol sensor is erratic at high rpm.  Do not make this value below fast idle speed, otherwise the ethanol content will never update correctly.



Both fuel and ignition can be compensated for ethanol content.




Ethanol fuel compensation

Specifies the fuel change based on the ethanol content for closed loop and open loop.  The exact compensation factors should be checked on a dyno with a wideband lambda meter.


Ethanol ECT compensation

Specifies the fuel change based on the coolant temperature (ECT), applied on the basis of 100% ethanol content. eg if this table contains a compensation value of 20% and the ethanol content is 75% then the fuel will be compensated 15%.


Ethanol vaporizes poorly compared to gasoline, has a higher latent heat of vaporization and also has a higher flash point, so ethanol fuels tend not to burn completely when the engine is cold. Unburnt ethanol sticks to the walls of the intake manifold / cylinder head or pass through the combustion chamber unburnt.  Because of this extra fuel needs to be injected into the engine to compensate for this.


Ethanol cranking compensation

Specifies the extra fuel while cranking.  Note that the cranking fuel is not compensated by the two open / closed loop fuel compensation tables above.


Ethanol cranking ECT compensation

Specifies the fuel change based on the coolant temperature (ECT), applied on the basis of 100% ethanol content. See the notes above on ethanol tuning and temperature.




Ethanol ignition compensation

Specifies the extra ignition advance based on the fuel ethanol content for closed loop and open loop.


Boost Compensation


The boost level can be adjusted based on the fuel ethanol content.



Ethanol Boost Compensation

Sets the boost level by interpolating between the low and high boost tables based on the fuel ethanol content. Note you must be using gear based boost control for this to work.  If a low/high boost input is used, it will override the ethanol boost compensation when switched to the 'high' settings.  On the 'low' setting the ethanol boost compensation will still function.  To disable the ethanol boost compensation when using flex fuel set the 'Boost low/high %' to 0.


Example: Using the above compensation table and a low boost table value of 10 lbs and a high boost table value of 15 lbs.  An ethanol content of below 15% will give 10 lbs boost. An ethanol content of 70% or higher will give 15 lbs boost.  An ethanol content of between 15% and 70% will give somewhere between 10 and 15 lbs boost.  eg If the ethanol content is 40% then the low to high boost interpolation value will be 42.5%, This will give a boost target of just over 12 lbs.