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Ethanol (E85) and AFR question

Understanding AFR

Discussion and questions related to the course Understand AFR


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Can you please answer my questions in layman's terms:

1. If a non-FlexFuel vehicle with OEM ECU is filled with E85, would the vehicle run lean but then utilize STFT & LTFT to correct the issue? Then throw CEL? Is that because narrow/wideband OEM ECU controller reads in LAMBDA and knows what to do?

2. If tuner leaves WB config for petrol and fills up with E85 & starts the car without adding any fuel to compensate... the tune is expected to be 40% more lean, so WB wold read about 20.58AFR? Once fuel target of 14.7 is reached we're really @ 9.7AFR. Correct?

So if a gas-only vehicle is filled with E85 (surprise!) it'll run 40% more lean? How do OEM ECUs fix this (if at all)? Is it because OEM O2 NB/WB controllers target 1.0 LAMBDA vs AFR and utilize fuel trims to solve the problem?

1. Yes, it will correct within the limits of STFT/LTFT as it tries to achieve Lambda 1 at part load. It does not know that it has other fuel. CEL will come on if the set LTFT limits are exceeded, usually around 20-25% of correction.

2. Lambda 1 is always lambda 1. With petrol it needs less volume than with E85, so if you try to start a car which has +/-0 LTFT on petrol with E85 it will either not start or take very long to start as you need much more volume of E85 to have a combustible mixture to allow the car to start.

OEM ECUs (and all good aftermarket ECUs) only use Lambda and therefore can compensate for different energy density of different fuels.

This, and many other benefits, is one of the main reasons why you don't use AFR but lambda as lambda is independent of the fuel being used. Stoichiometric combustion is what you are after, which is lambda 1.

Awesome, thanks for the clear answers. A few days later I clicked on the 'Ethanol & Flex Fuel Tuning - Fuel System Requirements' module and realized Andre answered my OEM ECU & Ethanol questions @ the 1:50-2:10min mark... in case anyone else was wondering.