How does boosting affect metering?

• A. It reduces fueling during boost
• B. It uses MAP/MAF data to adjust fueling but does not alter rail pressure
• C. It increases fueling using MAP/MAF data and may increase rail pressure
• D. It has no effect on fueling

Answer: (C)

Boosting increases the amount of air the engine can take in, so the fuel metering system must supply more fuel to keep the air-fuel ratio in the intended range. The engine control unit uses data from MAP (manifold absolute pressure) or MAF (mass airflow) sensors to know how much air is entering the engine and then calculates the required fuel quantity. As boost rises, these sensors indicate more air, and the ECU responds by increasing injector pulse width to deliver more fuel. In many systems, this higher demand can also push the fuel rail pressure up to maintain adequate injection pressure and atomization for the larger fuel flow. So boosting leads to more fueling with MAP/MAF data driving that adjustment, and rail pressure may rise as part of that response.