The output characteristics of the intake pressure sensor: In electronic fuel injection engines, the use of an intake pressure sensor to detect the intake volume is called a D-type injection system (speed density type). The intake pressure sensor does not directly detect the intake air volume like the intake flow sensor, but uses indirect detection. At the same time, it is also affected by many factors. Therefore, there are many price differences between pressure sensors and intake flow sensors in detection and maintenance, and the faults caused by them also have their own characteristics. When the engine is working, with the change of throttle opening, the vacuum degree, absolute pressure, and output signal characteristic curve in the intake manifold are all changing. But what is the changing relationship between them? Is the output characteristic curve positive or negative? This issue is often difficult for people to understand, resulting in some maintenance personnel feeling uncertain in their work. The D-type injection system detects the absolute and pressure inside the intake manifold behind the throttle valve. The rear of the throttle valve reflects both vacuum and absolute pressure, so some people believe that vacuum and absolute pressure are the same concept, but this understanding is one-sided. Under the condition of constant atmospheric pressure (standard atmospheric pressure is 101.3kPa), the higher the vacuum degree inside the manifold, the lower the absolute pressure inside the manifold. The vacuum degree is equal to the difference between atmospheric pressure and the absolute pressure inside the manifold. The higher the absolute pressure inside the manifold, the lower the vacuum level inside the manifold. The absolute pressure inside the manifold is equal to the difference between the atmospheric pressure outside the manifold and the vacuum level. That is, atmospheric pressure is equal to the sum of vacuum degree and absolute pressure. After understanding the relationship between atmospheric pressure, vacuum degree, and absolute pressure, the output characteristics of the intake pressure sensor become clear. During engine operation, the smaller the throttle opening, the greater the vacuum level in the intake manifold, the lower the absolute pressure inside the manifold, and the lower the output signal voltage. The larger the throttle opening, the lower the vacuum level in the intake manifold, the greater the absolute pressure inside the manifold, and the higher the output signal voltage. The output signal voltage is inversely proportional to the vacuum level inside the manifold (negative characteristic) and directly proportional to the absolute pressure inside the manifold (positive characteristic).
Post time: Mar-10-2025