Flex-Fuel E85 Conversion: Precautions to Take

The E85 conversion is a process that allows a vehicle to use two types of fuel: bioethanol and gasoline.

This conversion is carried out purely electronically, by modifying the ECU mapping to allow the user to drive with either fuel, in any proportion, without needing to make any manual adjustments.

E85 fuel, also known as superethanol, is composed of 85% ethanol and 15% gasoline. It is mainly produced from cereals such as corn.

The composition may vary depending on the season or even from one fuel station to another.

For example, in winter, the gasoline content is higher to facilitate cold starts.

Be aware that, in France especially, regulations have become more relaxed compared to the past. Fuel providers can now include a higher percentage of ethanol, which may lead to some issues—particularly during cold start phases.

It’s important to note that vehicles with older electronic management systems are more likely to experience issues than newer models, although it is still possible to make proper adjustments for compatibility.

When converting a vehicle to E85, certain precautions should be taken:

• Replace spark plugs if they have more than 20,000 km of use
• Replace ignition coils if they have more than 40,000 km of use
• Perform a datalog on both gasoline and E85 using the modified file
• Follow the adaptation phase between fuels (drive calmly for about 15 minutes after switching fuels to allow the ECU to adapt)
• On the day of conversion, make sure the vehicle is low on gasoline to allow for accurate logging and then refueling with E85 without an overly high ethanol/gasoline ratio
• Check whether the vehicle is mechanically capable of handling this modification, and if certain components may need to be replaced beforehand. For example, some vehicles may have a fuel pump or injectors that can’t supply enough fuel—E85 requires injecting 20 to 30% more fuel compared to gasoline

What parameters should be monitored when performing an E85 datalog:

• Engine RPM
• Injection values
• Injector flow rate
• High and low-pressure fuel pump flow
• Short and long-term fuel trims
• Lambda value (air-fuel ratio)
• Ignition timing advance
• Knock sensor values