The speed-density fuel-injection system uses the______ sensor as the primary sensor to determine base pulse width.
A. TP (throttle position)
B. MAF (mass air flow)
C. MAP (manifold absolute pressure)
D. BARO (barometric)
The correct answer and explanation is :
Correct Answer:
C. MAP (Manifold Absolute Pressure)
Explanation:
The speed-density fuel injection system determines the appropriate amount of fuel to inject into the engine by using engine speed (RPM) and intake manifold pressure to calculate the air density. The Manifold Absolute Pressure (MAP) sensor is the primary sensor in this system because it measures the pressure (or vacuum) inside the intake manifold, which correlates to the amount of air entering the engine.
How the MAP Sensor Works in a Speed-Density System:
- Measuring Intake Pressure:
- The MAP sensor detects the absolute pressure inside the intake manifold.
- When the throttle is opened, the manifold pressure increases, indicating more air entering the engine.
- When the throttle is closed, the pressure drops (higher vacuum), indicating less air entering.
- Calculating Air Mass:
- The engine control module (ECM) uses the MAP sensor reading along with engine RPM to estimate the air density.
- This information helps determine the correct amount of fuel to inject for optimal combustion.
- Adjusting Fuel Injection Pulse Width:
- The pulse width refers to the duration the fuel injector stays open.
- The ECM adjusts the pulse width based on MAP readings to maintain the correct air-fuel ratio.
Why Not Other Sensors?
- Throttle Position Sensor (TP): Provides throttle position data but does not measure actual air intake.
- Mass Air Flow (MAF) Sensor: Used in mass air flow systems, not speed-density systems.
- Barometric (BARO) Sensor: Measures atmospheric pressure but does not directly determine intake air density under varying engine loads.
Since the MAP sensor is essential for calculating fuel delivery in speed-density systems, it is the correct answer.