What is the normal value of absolute pressure in the car intake pipe?
3 Answers
Engine intake manifold vacuum should normally be between 64-71kPa. 1. Working indicators: If a certain cylinder is malfunctioning, the single-cylinder cut-off method can be used for diagnosis. After cutting off a single cylinder, the greater the drop in Px, the better, which serves as an indicator of each cylinder's performance (ignition, fuel injection, sealing). Quickly open and close the throttle. 2. Measuring vacuum: Located in the engine compartment, it is connected to the intake manifold via a vacuum tube or directly installed on the intake manifold behind the throttle. It measures the absolute pressure in the intake manifold behind the throttle, detecting changes in absolute pressure within the manifold based on engine speed and load.
As someone who frequently works on my own car, the normal values for absolute intake manifold pressure can really vary! At idle, once the engine warms up, it typically stabilizes between 20 to 25 kPa. During acceleration, the pressure climbs, approaching the atmospheric pressure level of around 100 kPa. Don’t expect a fixed number—higher altitudes reduce the pressure, and engine temperature has a big impact too. When I check it myself, I use a simple pressure gauge or an OBD tool to read the values. The biggest worry is a vacuum leak—if the pressure is too low, it could mean a leak in the piping, and if it’s too high, the sensor might be faulty. Proper pressure ensures the right air-fuel mixture, making the car run smoothly, fuel-efficiently, and eco-friendly. Remember the normal fluctuations, but if the pressure suddenly spikes or drops and the engine light flashes, pull over immediately to check—it’ll save you from a roadside breakdown and costly repairs.
I've been driving daily for over ten years, and the normal value of intake manifold absolute pressure depends on driving conditions. At idle, it's around 20 kPa. When accelerating from a stop, the pressure jumps up, and when driving at about 80 km/h, it approaches 100 kPa. This pressure is related to the engine's air intake volume, affecting both vehicle power and fuel consumption. If you notice the pressure is consistently low, you might experience difficulty starting or lack of power when climbing hills; if it's too high, it can cause abnormal combustion and shaking. Safety first—during maintenance, I always ask the mechanic to check the pressure. Using a diagnostic tool, error codes can be quickly identified. Don't attempt to disassemble anything yourself, as aging vacuum hoses or dirty sensors can disrupt the pressure. Keeping an eye on this ensures safer driving, extends engine life, and saves money.
