Ethanol content learning based on engine roughness

A method for ethanol content learning based on engine roughness comprising the steps of:

• establishing a trigger threshold based on engine speed and manifold pressure;
• establishing a fix threshold based on engine speed and manifold pressure;
• obtaining a first measured roughness;
• incrementing fuel delivery by a first amount based on a first estimated fuel-to-air ratio;
• obtaining a second measured roughness after incrementing fuel delivery;
• resuming normal fuel delivery if said second roughness is greater than the trigger threshold;
• incrementing fuel delivery by a second amount based on a second estimated fuel-to-air ratio if said second measured roughness is not greater than said trigger threshold and greater than said fix threshold;
• obtaining a third measured roughness after incrementing fuel delivery by a second ethanol amount;
• and
• incrementing again said fuel delivery by said second ethanol amount if said third measured roughness is less than said trigger threshold but greater than said fix threshold.

A method for ethanol content learning based on engine roughness comprising the steps of:

• establishing a trigger threshold based on engine speed and manifold pressure;
• establishing a fix threshold based on engine speed and manifold pressure;
• determining a first measured roughness;
• monitoring measured roughness if measured roughness is less than a trigger threshold;
• incrementing a fuel modifier by a first fuel offset if said engine roughness is greater than said trigger threshold;
• determining a second measured roughness after incrementing said fuel modifier by said first fuel offset;
• resuming normal fuel delivery by adjusting said fuel modifier and exiting said method if said second measured roughness is greater than said trigger threshold;
• incrementing said fuel modifier by a second fuel offset if said second measured roughness is greater than a fix threshold;
• determining a third measured roughness;
• resuming normal fuel delivery by adjusting and exiting said method if said third measured roughness is greater than said trigger roughness;
• re-incrementing said fuel modifier by said second fuel offset if said third measured roughness is less than said trigger roughness and is greater than said fix threshold;
• and
• maintaining said fuel modifier at a current value if said third measured roughness is less than said trigger roughness and is less than a fix threshold.