The Correct Answer and Explanation is:
The correct answer is B. Richer air/fuel mixture.
Explanation:
A Mass Air Flow (MAF) sensor is a critical component in a modern engine management system. Its primary function is to measure the mass of air entering the engine. The Engine Control Unit (ECU) uses this data as a primary input to calculate the precise amount of fuel to inject for efficient combustion.
The issue described is a “poor ground” on the MAF sensor’s ground wire. Here is a step-by-step breakdown of why this leads to a richer air/fuel mixture:
- Understanding a Poor Ground: A poor ground means there is excessive resistance in the ground circuit. Instead of providing a clear, near-zero volt reference point, the resistance causes a voltage drop as the sensor’s operating current flows through it. This “lifts” the sensor’s ground reference to a voltage potential above the true chassis ground (e.g., 0.5V or 1.0V instead of 0V).
- Impact on the Signal Voltage: The MAF sensor generates an output signal (typically a variable voltage) that is sent to the ECU. This signal voltage is referenced to the sensor’s own ground. The ECU, however, reads this signal voltage relative to its own stable ground. Because the sensor’s ground is now elevated, the ECU reads a signal that is the sum of the intended signal plus the ground offset voltage. This results in the ECU seeing a falsely high voltage signal.
- ECU Interpretation: The ECU is programmed to interpret a higher voltage from the MAF sensor as a greater mass of air flowing into the engine.
- Fuel Calculation and Result: Based on this false high-airflow reading, the ECU will calculate that more fuel is needed to maintain the target air/fuel ratio (e.g., 14.7:1). Consequently, it commands the fuel injectors to stay open longer, injecting more fuel into the cylinders. Since the actual amount of air has not increased, this excess fuel creates a richer air/fuel mixture.
In summary, the poor ground biases the sensor’s signal high, tricking the ECU into thinking there is more air than there actually is, which causes it to over-fuel the engine.
