Motronic Fuel Maps

Motronic fuel maps from a factory U.S. Carrera program optimized for use with an oxygen sensor and catalytic converter.  The part throttle fuel map is mostly flat and designed to maintain a lean stiochiometric air/fuel ratio of 14.7:1 through the low and mid load regions to assist the O2 sensor, for low emissions and good fuel economy but not for power or throttle response. The upper rpm high load regions are set to go rich, countering the trim back adjustment of the O2 sensor.

Fuel maps from a factory European Carrera 3.2 without O2 sensor and catalytic converter.  The part throttle fuel maps are richer under high part throttle loads for increased torque and throttle response over the U.S. cars.

Performance fuel maps are modified and remapped for maximum performance and power. Reworking these regions bring great benefits in overall power and drivability because here is where the majority of drivers spend at least 95% of the time. The low load region (<25%) is kept virtually stock to maintain factory emissions and fuel economy while cruising on the highway or around town. For the O2 sensor equipped motors, the sensor keeps the fuel mixture at a stoichiometric 14.7:1 for the best balance of fuel efficiency, emissions and acceptable power. However, upon demand, when maximum power is called for at higher engine loads such as during acceleration, the max power air/fuel ratio of 12.8-13.0:1 is delivered on demand for maximum throttle response, torque, and horsepower. This produces the best balance of fuel efficiency and emissions, while delivering maximum power on demand. Our chips idle cleanly without an overly rich mixture. You won't have a lean spot from 1200 to 2000 rpm causing off idle bog, and most importantly avoid the dangerously lean tendency at high rpms under full loads.

The following chart displays the differences in the factory full throttle fuel mapping between a U.S. spec catalytic converter equipped motor, and a European/ROW spec motor with a premuffler instead of a catalytic converter. Because full throttle is where most drivers are at less than 5% of the time, the full throttle fuel map should be optimized for full power and not for emissions. However, because of the more restrictive cat, and in the interest of low emissions, U.S. chips are programmed leaner below 4000 rpm than their ROW counterparts to maintain the emissions friendly stoichiometric ratio. Reoptimizing this region often brings increases of 6-10 ft-lbs of torque. After 5200 rpm though, the U.S. curve is excessively rich as the excess fuel helps to keep the ceramic monoliths of the catalytic converter cool under hours of sustained wide open throttle operation near redline on the Autobahn. As most owners do not drive nonstop for hours at 150 mph with a catalyst, optimizing the air fuel ratio in this region especially with stock motors, increases the total hp under the curve significantly, with typical gains of 16 hp at 6000, increasing to 25-35 hp in the 6400 rpm zone.

Full throttle is signaled to the DME by the activation of the full throttle microswitch at the throttle butterfly. At full throttle most input sensors are ignored, including the O2 sensor. The DME thus references the full throttle fuel map that has been preprogrammed for the stock setup. This means that no matter what modifications one performs to a motor, including exhaust modifications and displacement increases, no additional fuel will be injected and horsepower increases will be limited. When engine modifications increase airflow into the engine, such as by sport exhausts and intake modifications, it thus becomes necessary to reprogram the amount of fuel injected to maintain the optimum air/fuel ratio. If this is ignored, the danger exists of an excessively lean running engine at full load, leading to increasing combustion chamber temperatures, and thus the risk of engine damage by predetonation.

Adjusting the DME to meet new boundary conditions such as those presented by sport mufflers, European premufflers or cat bypasses, headers, high flow catalytic converters, and higher octane fuels will in such instances open new potential for increased power gains by optimization.