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Your Boost pressure sensor worn out? » Read more about common malfunctions • Repair • Replacement manual
Perfect engine control with the manifold pressure sensor The manifold pressure sensor or pressure gauge is an important component controlling the amount of fuel being injected into the combustion chambers. It measures the pressure in the manifold and transmits the data to the control unit. These pressure data are used by the control unit to calculate the amount of air intake and the necessary fuel amount. This leads to lower fuel consumption and cleaner exhaust. The manifold pressure sensor is an alternative to the air-flow sensor. Task of the manifold pressure sensor The manifold pressure sensor determines the air flow intake in the combustion area of the car. The air intake can only actively be regulated by the throttle valve. For modern cars this is not sufficiently accurate, especially for the sake of cleaning the exhaust. Air and fuel amounts must always stand in a certain relation to each other. Too much injected fuel causes the combustion to be too "rich". The result is an excess of soot potentially clogging the catalytic converter. Furthermore, unburnt fuel might remain in the catalytic converter and in case of ignition could cause damage to the platinum layering. If too little fuel is injected, the combustion is too "lean", causing lower engine performance while simultaneously the engine is heated up strongly. To supply the engine with the ideal air-fuel mix, the intake manifold pressure sensor is essential. Difference between air-flow sensor and pressure sensor Both sensors have a similar task: measuring the air intake and permanently transmitting the results to the control unit. In an air-flow sensor the air stream is conducted past a heated platinum wire. The sensor measures the extent in which this wire is being cooled by the air mass. By comparing the target and actual value the control unit calculates the amount of air intake. In a pressure sensor the internal pressure in the intake manifold is measured by membranes. Position of a pressure sensor The pressure sensor is flanged sideways on the intake manifold. In small cavities like the intake manifold it can safely be assumed that the pneumatic pressure is evenly distributed. The sensor is only connected to the intake manifold with a plug contact or a bolt. The wire connection with the control unit is established by a simple multi-plug. Its replacement is accordingly simple. Defects of the intake manifold pressure sensor Tightening of exhaust regulations caused high investment in exhaust technology. The manufacturers are permanently looking for possibilities to reduce the emission of pollutants and to meet the strict specifications. One of the measures for cleaning the emissions was the introduction of the EGR valve. This exhaust gas recirculation valve conducts part of the emissions back into the combustion chamber via the intake manifold. Occurring soot particles are burnt again and rendered harmless for the environment. In praxis this functions adequately, but has a disagreeable side-effect: the recirculation causes soot to deposit in the intake manifold. This affects most adjacent components: intake manifold, suction pipe, throttle valve and unavoidably the intake manifold pressure sensor as well. In modern cars, especially with diesel drive, regular cleaning of the intake system is necessary. Technically simple parts like the intake manifold or throttle valve can be cleaned easily at all times. A sensitive part like the manifold pressure sensor with its membranes is more difficult to clean. Therefore cheap spare parts are being made available by the industry. Pinching off the EGR valve? Some drivers pinch off the EGR valve to avoid the re-occurring pollution of the intake tract. This constitutes an interference of engine control and the exhaust system of the car. The action can cause damage to the catalytic converter and replacing it can turn out to be considerably more expensive than cleaning or replacing the intake manifold components. Furthermore it might have consequences for the operation authorisation of the car. Police finding a pinched EGR valve might impose a penalty. Buying a new intake manifold pressure sensor Cleaning the intake system is cumbersome and dirty, but relatively simple. The replacement of a manifold pressure sensor is also very simple. If it cannot be cleaned, it can be bought for ca. 20 euro (£ 17). For such a price, risky measures like pinching off the EGR valve are really not worthwhile.