What is the normal value of engine intake manifold vacuum?

The normal value of engine intake manifold vacuum is between 64-7 1 kPa.

If a cylinder is not working properly, it can be diagnosed by single cylinder flameout. After the single cylinder is turned off, the greater the drop value of Px, the better. This is an index to judge the quality of each cylinder (ignition, fuel injection and sealing). Quickly open and close the throttle. If the pointer swings sensitively between 6.7-84.6 kPa, it shows that Px has good following performance to the change of throttle opening, that is to say, the sealing performance of all parts is good under all working conditions.

If the seal is not good, Px is lower than normal at idle speed, which is obviously unstable. When the throttle is opened quickly, the pointer will drop to zero, and the pointer will not return to 84.6kPa after the throttle is closed. In order to verify the tightness of each cylinder, the vacuum gauge should be replaced at the hole of the dipstick, and the pressure measured in the crankcase should be negative pressure; If it is positive, it means that the sealing is not good, or the PVC is not well ventilated.

Extended data

Numerical characteristics of vacuum

Stability of 1 and p (vacuum degree)

△P is formed by the joint action of * * when each cylinder alternately takes in air. Obviously, it is normal for δP readings to fluctuate regularly and rhythmically. The more cylinders, the better the stability of △P reading; With the increase of engine speed n, the reading of △P tends to be stable.

2. Typical value of P at idle speed

Under the normal idle speed of an engine with good technical condition, the typical value of △P should be stable at 60 ~ 70 kPa, depending on the idle speed. Under the stable working condition of the engine, the △P value of idle working condition is large and stable, which has strong comparability and is sensitive to the cause of △P abnormality. Therefore, idle △P value is one of the important diagnostic parameters for engine △P fault diagnosis.

3. Typical value of P under the conditions of rapid acceleration and rapid deceleration.

From △P=f(α, n), α remains unchanged, and N increases △P increases; When n is constant, α increases and △ P decreases; For two parameters α and N, as long as one of them is fixed, we can measure or observe the change or follow-up of △P with the other parameter. But the difficulty of operation is that α and n are positively correlated and inseparable. Fortunately, according to the principle of inertia of objects, through the operation of slamming on the throttle and slamming off the throttle, we can think that α and n are close to separation in an instant, so we can read or observe the magnitude or follow-up of δ p changing with α and n respectively.

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