E85 flex fuel tuning

It is not free — what you need to know

Ethanol carries less energy per litre than petrol, so more fuel must flow for the same power. That immediately raises the question of whether the fuel system — pump and injectors — can meet the new demand. If the system runs out of headroom the mixture goes lean, and that is genuinely dangerous.

So the first thing we look at for an E85 tune is fuel system headroom. In the datalog we track injector duty cycle and rail pressure at high load; if there is no headroom, we reduce the blend ratio or recommend hardware.

The second issue is blend consistency. Ethanol content varies from station to station. With a calibration built for a fixed ratio, a different blend in the tank can produce behaviour you did not expect. We need to know what you can reliably get hold of.

Cold starting is also harder on ethanol: low temperatures need extra fuel for the first fire, and that behaviour is calibrated separately.

E85 questions

Do I need to change hardware?

At lower ethanol ratios usually not. As the ratio climbs the fuel system becomes the limiting factor, and it would be wrong to give a firm answer without seeing your datalog.

Can I switch between petrol and E85?

Without a fuel composition sensor you need to stay with whatever blend the calibration was built for. Free switching requires hardware that measures the blend in real time.

Will my fuel consumption increase?

Yes, noticeably — ethanol has a lower energy density.

Will E85 damage my engine?

Not while the fuel system can meet demand and the calibration is right. The risk comes from running lean on insufficient fuel supply.

Related pages

• Datalog analysis — checking fuel headroom
• Stage 2 remap — with hardware changes
• BMW remapping guide — technical background