VW AG EA888 Flex Fuel

Owned by Lucan Hetherington
Last updated: Sept 18, 2024
8 min read

Finally flex fuel has been released, and is now available on V4.1 patches. This introduces flex fuel sensor input and fuel, ignition boost and torque controls as an output in hardcoded maps. Flex Sensors can be input via the pin A71 on the ECU, via CAN inputs or a fixed value.

Hardware

Unless you are specifying ethanol blends only external hardware will be required to use Flex Fuel, the recommended hardware would be

https://www.cobbtuning.com/products/fuel-system/flex-fuel-upgrade-kit-for-volkswagen-mk7-mk7-5-gti-jetta-a7-gli-mk7-mk7-5-golf-r-audi-a3-s3-8v

If you wish to use a CAN based sensor there are many available options such as

https://zeitronix.com/Products/ECA/ECA2CAN.shtml

Other hardware to support ethanol content changes may be required, on our dev car we use a COBB flex fuel kit and with a hybrid turbo, an intake and stock injectors the standard LPFP seemed to run out of flow and the pressure start to drop at about 30% ethanol.

Map List

image-20240618-111529.png

Enabling Flex Fuel

There are 3 methods to obtain a ethanol content allowing the flex fuel code to run. To enable Flex fuel outputs simply select the option which you wish in the FlexFuel Control (RaceROM) map, then configure the input. You can chose different methods for each MS mode if desired.

  • Fixed Value

  • CAN Sensor

  • Pin A71 on ECU

image-20240618-112103.png

You will also need to move the fuel quantity monitoring values of MPI reference Fuel Flow Offset map out of the way to allow RaceROM code to increase the fuel volume delivered without causing DTCs and limp modes.

Fixed Values

Using a fixed value requires that you specify the ethanol content in each MS mode (1-4) using the FlexFuel Ethanol Fixed Value by MapSwitch Mode map, you only need to set a value in the MS mode that is using a fixed value (in the case above MS mode 2)

CAN bus based Sensor

To set up a CAN bus based ethanol content sensor you can use any CAN equipped device to transmit the ethanol content to the ECU over CAN. there are several default options available in the CAN inputs function of RaceROM for more information on setting up the CAN equipment see the link below.

wiring for the CAN input needs to be made into the power train CAN bus direct to the ECU. For more information on this please see the link below

Pin A71

Pin A71 is the native pin for an ethanol content sensor in the Simos ECU’s (both 18.1 and 18.10) this normally unused pin can be connected directly to the output of a continental flex fuel sensor (frequency and duty output) and converted into an ethanol content and fuel temperature signal. There are many plug an play kits available for VW flex fuel which utilize pin A71, the recommended kit is.

https://www.cobbtuning.com/products/fuel-system/flex-fuel-upgrade-kit-for-volkswagen-mk7-mk7-5-gti-jetta-a7-gli-mk7-mk7-5-golf-r-audi-a3-s3-8v

These kits have the wiring (power ground and signal) instructions in their own kits so make sure to get the install instruction from your supplier and follow them exactly.

to enable Pin 71 in the software you will need to set the

  • FlexFuel Control (RaceROM) map to Ethanol Sensor Pin (A71)

  • Check the Enable Special Features → A71 Pin Enable checkbox

  • Ethanol Sensor Flag 1 (lc_fac_afu_ratio_conf) this should be '1' by default, it needs to be '0'

  • Ethanol Sensor Flag 2 (lc_fac_afu_ratio_man_act) this should be '1' by default, it needs to be '0'

After these values are set the ethanol content of the fuel can be seen in the logs.

ECU Connect Ethanol Content Display

You can also set up the gauges on the MFD to display ethanol content on MS mode change or using ECU Connect.

FlexFuel Fuel Quantity Multiplier

The fuel quantity supplied for a set ethanol content can be set using the FlexFuel Fuel Quantity multiplier map. This value multiplies the fuel amount, allowing you to match the extra quantity required by ethanol mixtures and keeping the trims as close to 0 as possible.

Flex Fuel Boost Control

The Hardcoded flex fuel feature allow for per map switch mode ethanol content boost target limtis to be applied, these FlexFuel Boost Target Max Mode 1-4 maps are the maximum allow boost target at the maximum value of the blend map

The Blend map specified what proportion of the Boost target max for that MS mode is applied

The final value from this and the normal MS mode boost target limit maps is set by the map output and the following calculation:

Final RR boost Target limit = (Boost target limit Mode # Map *( 1 - FF Boost Limit blend)) + (FF Boost Limit Blend x FF Boost Target Limit)).

OEM boost limits and Charge Pressure setpoints must be lifted to give enough headroom to achieve you flex boost target as well.

Flex Fuel Cranking

Extra fuel is sometimes required for cranking above the normal quantity multiplier to set a higher fuel volume for cranking to try improve cold starts at high ethanol contents the FlexFuel Cranking Multiplier map has been added.

The value from this map is then reduced to 0 once the FlexFuel Cranking RPM threshold has been exceeded,

The correction amount is then decremented to 0 at the rate defined in the FlexFuel Cranking Multiplier decay rate map

Flex Fuel Fuelling

Lambda Target

You can then set up Fuel target changes for each Map switch mode using the FlexFuel Lambda Base Set Point Mode 1-4 maps a blend map for that ethanol %.

The Blend map is then used to calculate the value between the normal and FF Lambda target maps.

Final Lambda Target = (Lambda Tgt *( 1 - FF Fuel Map blend)) + (FF Target Lambda Blend x FF Target Lambda)

MPI/DI Split

You can also adjust the MPI to DI split for different ethanol content to take the fuel load away from the DI system. to do this simply ensure that the combustion modes are set to have MPI/DI splits active and that the injectors are set up correctly then use the FlexFuel MPI DI split Normal/Warmup map to increase or decrease the split percentage as required.

the Blend map specified which proportion of the OEM map and the FF map are applied as a final value

Final MPI DI Split = (OEM MPI DI Split *( 1 - FF Fuel Map blend)) + (FF MPI DI Split Blend x FF MPI DI Split)

Start of Injection

The DI system start of injection angle can also be increased to try accommodate the extra fuel volume required by ethanol content. The Start of injection for full ethanol content (on the blend map) is specified by the FlexFeul start of Injection HPDI map. the values in the map will be blended with the OEM values and the final value used as the start of injection.

The Blend map specified which proportion of the OEM map and the FF map are applied as a final value

Flex Fuel Ignition

Flex Fuel ignition timing maps to match the MS mode ignition timing maps are also now available, set the maximum ignition timing for the maximum ethanol concentration and use the blend map to deliver the correct timing for the ethanol concentration for each map switch mode.

The Blend map specified which proportion of the OEM map and the FF map are applied as a final value

The Final Ignition value

Final Base Ignition = (Ignition Angle (Flap and lift) Map (Mode # ) * ( 1 - FF Ignition Timing Base blend)) + (FF Ignition timing Blend x Ignition Angle (Flap and lift) Map (Mode # ))

Flex Fuel Knock detection

You can adjust the knock threshold for ethanol to allow for the changes in knock response generated by the change in combustion noise. The FlexFuel Low knock thresholds and Knock threshold maps are blended with the OEM knock threshold maps using the blend functions

The Blend map specified which proportion of the OEM map and the FF map are applied as a final value

Flex Fuel Torque Control

To increase the torque demand to allow for the greater torque produced when using ethanol fuels simply use the FlexFuel Torque Demand Limit Normal/Sport maps these Flex maps are blended with the RaceROM torque maps to generate a final value.

The Blend map specified which proportion of the RR Torque Demand Limit Normal/Sport maps and the FF map are applied as a final value.

Flex Fuel Ethanol content Hold

In some cases the flow through the flex sensor can effect the reading at load and cause the car to see an incorrect value of ethanol at load (more for sensor installed in fuel return lines etc). To counteract this an Ethanol content Hold function is employed where above the Flex Fuel Ethanol content Hold RPM/Mass Air Charge threshold the ethanol content is not update by the sensor.

Once the load/rpm decreases again the ethanol content is updated normally

Custom Maps Processing

Ethanol content can be added used in custom maps, as an input and an output (so you can set a content value if you want)

This functionality can then be used to effect things like WG duty to compensate for the change in exhaust energy when perfecting your flex boost control.

Support Feature Requests and Bugs

Please send support requests about how to use the features above, problems with the features or feature requests to Support@ecutek.com.