The Manifold Absolute Pressure Sensor (MAP) is connected to the intake manifold via a vacuum tube. It senses changes in vacuum within the intake manifold as the engine speed and load vary. The sensor converts these changes in internal resistance into a voltage signal, which the ECU (Electronic Control Unit) uses to adjust fuel injection and ignition timing. In other words, the ECU outputs 5V to the MAP sensor, and the signal terminal detects the voltage value. When the engine is idling, the voltage signal is approximately 1-1.5V, and when the throttle is fully open, it is approximately 4.5V.
The intake pressure sensor detects the absolute pressure in the intake manifold behind the throttle valve. It detects changes in the absolute pressure in the manifold based on engine speed and load, and then converts them into a signal voltage, which is sent to the engine control unit (ECU). The ECU controls the amount of basic fuel injection based on the magnitude of this signal voltage.
What are the signs of a faulty intake pressure sensor?
1. The sensor's internal wiring is open-circuited or short-circuited;
2. The sensor output signal must not change with the vacuum level of the intake manifold;
3. The voltage of the sensor output signal is too high or too low, and its value deviates from the normal range.
In addition, an open or short circuit in the connection line between the intake manifold pressure sensor and the computer, blockage or leakage in the vacuum hose between the sensor and the intake manifold, or blockage of the intake manifold vacuum port can also cause abnormal sensor output signals.
When the intake manifold pressure sensor malfunctions as described above, it can cause abnormal fuel injection in the engine control unit (ECU), resulting in phenomena such as an overly rich or lean air-fuel mixture, abnormal engine idling or poor acceleration, backfire in the intake manifold during engine operation, or black smoke from the exhaust pipe. Faults caused by a faulty intake manifold pressure sensor itself or its wiring mainly include: engine failure to start, sluggish engine acceleration, unstable engine idling, and intermittent engine stalling.
The causes of pressure sensor failure include: vacuum leakage at the intake manifold preventing the intake manifold pressure sensor from obtaining a correct vacuum signal; leakage or detachment of the vacuum hose; and incorrect connection between the intake manifold pressure sensor hose connector and the charcoal canister connector.
