Effect of air and fuel injection pressure variation on torque and fuel economy in spark-ignition engines

Because of decreased air density and altered engine control behaviour, the efficiency of traditional multi-point injection (MPI) spark-ignition engines can degrade at great altitude, therefore increasing CO2 and fuel consumption. Using a pressure regulator and an Arduino-based MAP-signal conditioning module on a Great Wall Wingle 5 tested in Quito, Ecuador (2,850 m a.s.l.), this study assesses a low-cost outside intervention that changes fuel-rail pressure (3.2–5.0 bar). Real-road tests on urban and highway routes were carried out following an SAE J1321-inspired approach, noting fuel economy, torque response, and injection pulse behaviour across pressure levels. Together with shorter injection pulses, raising pressure to 5.0 bar enhanced fuel economy from 7.18 to 13.45 km/l on the urban route (≈ 87.3%) and from 9.19 to 12.89 km/l on the highway route (≈ 40.3%); low-RPM torque, however, showed tiny fluctuations in heavy traffic. The 4.5 bar setting struck a more stable middle ground without sacrificing most of the efficiency advantage. Results should be regarded as case-specific and require validation under regulated circumstances and a bigger fleet before generalisation as the investigation is founded on a single car and limited paths without long-term durability testing or direct tailpipe readings.