With many of the MQB based vehicles, VW Auto Group adopted the standard that so many Japanese cars used for decades. There are better versions available worldwide than in the US. In this case, some cars had multi-port injection, but in this specific case, some had Flex Fuel. We’ve gone ahead and added that feature to the US cars so you can enjoy the benefits of ethanol in your car without needing to move overseas.

Rather than needing two completely separate tunes, flex fuel tuning for MQB heavily utilises the pump gas tune for the basics, and then compensations are added by the factory computer, and the flex fuel tables to optimise operation. Since tuning builds off of your existing pump gas tune it’s recommended that you first tune the car on pump gas, then move on to ethanol.

Enabling Flex Fuel

To enable flex fuel on your map will take touching (or double-checking) a few different tables, but is a simple 1 or 0 effort.

1. Flex Fuel Sensor Enable needs to be set to 0 to allow the sensor to read ethanol.
   
   

   Open

   

   Flex Fuel Sensor Enable must be set to 0

   
   
   

2. Master Switch (Flex Fuel) changed to 1 in order to enable flex fuel calculations
   
   

   Open

   

   
   
   

3. Verify Manual Ethanol Content is set to 0 and the Manual Ethanol Content Switch is disabled (0) which sets it to read from the sensor instead. Either of these can interfere with the system calculating.
   
   

The Factory Fuel System

Utilizing existing pins in the ECU, the ethanol content sensor sends an update of the fuel’s chemistry from the feed line to the high pressure fuel pump, straight to the ECU. Because this is a returnless fuel system stock, it’s important to remember that there is always going to be some amount of fuel between the sensor and the engine. While not an issue once the ethanol has mixed into your tank of fuel, as the fuel goes through the process of mixing and evening out, you may have a fairly different ethanol content going through the engine than what is being read at the sensor. Most of the time if you’re targeting a similar ethanol content with the fuel being added to the car, this won’t be much of an issue. However if you’re going from 0% ethanol to 85%, it may be a good idea to give the ethanol content some time to stabilize.

Fueling Adjustments

Due to a change in it’s ideal air to fuel ratio, Ethanol requires an increase of ~30% fuel, however compensation for that extra volume and compensation for startup in cold weather is built into background calculations in the system, so the only changes a basic car will need (assuming you’re starting from a good pump gas tune) is if you want to adjust the fuel ratio to make additional power.

Flex Fuel AFR Addition Table

This table allows you to adjust the target air fuel ratio for the vehicle when using flex fuel. The changes are made in AFR and only positive changes are allowed (which lean the mixture out). Typically you’re able to gain additional power on ethanol by leaning the air fuel ratio out slightly so this allows you to do that based on airflow and RPM.

This table serves as a base which is adjusted by the Flex Fuel AFR Ethanol Blend Percentage table. This allows you to use a different percentage of the AFR addition table depending on the Ethanol content. In most cases you’d want to use a higher percentage of the adjustment as ethanol increases.

Flex Fuel Torque Adder

The MK7 and MK7.5 vehicles have engine management systems that are based around torque requests and torque output. This means that in an ideal (and simplified) world the driver “asks” for torque with the accelerator pedal and the engine does what is required to achieve that output in terms of boost and ignition timing. However on the flip side, unless you ask for more torque,

Operating with a different value based on RPM and Gear, you can add torque to different portions of the range and speeds. This table gets multipled against two different tables

To get the final torque adder you’ll have both the Ethanol content and throttle position blend percentages multiplied against the torque adder.

Boost Control and Flex Fuel

Flex Fuel Maximum Intake Manifold Pressure Setpoint

A setpoint which gets blended with the OEM IM setpoint based on the blend percentage table It will only ever blend the target maximum intake manifold setpoint between the OEM one, and the new ethanol one.  So if you want to be able to reduce power output and target a lower intake manifold setpoint (for example, if you’re on a stock fuel system and can’t keep up with full E85) you’ll need to drop the OEM im setpoint to what you want the lowest value to be.  You can then blend some of the ethanol content setpoint back in at a lower ethanol content (E0, E10) in order to make up for the reduction.  When you do that it will add a percentage of the FF setpoint to the reduced stock setpoint bringing the level back up to what it would have been before you initially reduced the target.  From there use a higher percentage of the adder to increase power output when your fuel system allows, and use a lower percentage of the adder as the fuel system runs out of injector room.

Flex Fuel PUT Adder

Adds to the target Pressure Upstream Throttle value for the car. Currently MK7 and MK7.5 cars operate slightly differently due to a variance in the ECU.

MK7 (COBB01)
The PUT setpoint is set based on the final OEM intake manifold setpoint (without the FF adder).  This means to run a higher PUT target you’ll need to use the Flex Fuel Put Adder.  This gets exacerbated when using a lowered OEM IM Setpoint to reduce power at high ethanol contents, so this number will typically be larger on a MK7 than a 7.5

MK7.5 (COBB02, 8V09096259Q)
The OEM and FF intake manifold setpoint are both used to establish the PUT setpoint, so typically much less PUT adder is required to raise power.

Ignition Adjustments

One of the benefits of ethanol is a higher knock resistance (referenced as the octane in the US) compared to gasoline. Pump gas his fairly easy to understand and has options from 87-93 commonly available depending on where you live. Ethanol has an effective octane rating of ~107, making it a pretty good proposition for many people (especially given the prices of high octane race gas). This means in order to optimize you’ll likely want to adjust the ignition timing as ethanol increases.

The Flex Fuel Ignition Adder table establishes an amount to add to the ignition timing of the vehicle based on RPM and airflow. It has a single blending table that blends in a percentage of the ignition adder based on ethanol content.

Misc Flex Fuel Tables and Toggles

Enable Ethanol Sensor Diagnostics is a toggle found under the Advanced Engine Parameters heading in the software. This toggle allows you to enable the DTC options for the ethanol content sensor, assisting with troubleshooting during inital setup, or will help the driver be more aware of hardware failures ahead of time. The DTCs that are enabled can be found here: https://cobbtuning.atlassian.net/wiki/spaces/PRS/pages/3152478426

Maximum Ethanol Content (DTC) sets a limit. Upon exceeding this limit of ethanol content you will get a check engine light on the dash as well as the identifier _ _ _ _ . This will only be enabled if you check the toggle for Enable Ethanol Sensor Diagnostics. Alternatively setting a value of 101% would prevent this from being set in the event that you don’t want a DTC for ethanol limit but want the diagnostics enabled for the other benefits it offers.

Threshold to Update MFF Value sets an amount by which the ethanol content needs to change before the ethanol content the system is using will update. For example, if you set the threshold to 2, and the ethanol content changes from 30% to 32% the system will continue using 30% ethanol. However as soon as it breaches that 2% threshold (let’s say 32.1%) it will now change the calculations to be based off of 32.1%.

Flex Fuel Ethanol Hold Content Boost

Once boost pressure exceeds this limit (or the hold content for RPM) the ECU will stop updating the ethanol content and utilize the last read value for all of it’s calculations. This can be helpful to avoid the computer making rapid swings in compensation for ethanol content which can happen under many circumstances (if the fuel in your tank isn’t mixed well, is contaminated or poor quality).

Flex Fuel Ethanol Hold Content RPM

Once engine RPM exceeds this limit (or the hold content for Boost) the ECU will stop updating the ethanol content and utilize the last read value for all of it’s calculations. This can be helpful to avoid the computer making rapid swings in compensation for ethanol content which can happen under many circumstances (if the fuel in your tank isn’t mixed well, is contaminated or poor quality).