The purpose of this test is to evaluate the intake manifold pressures of a naturally aspirated gasoline engine during idle conditions using the WPS500X pressure transducer.
This known good waveform has the following characteristics:
0 bar is expressed as a relative pressure and indicates atmospheric pressure.
An average intake manifold pressure around -700 mbar (i.e. a vacuum, relative to atmospheric pressure).
A series of small depressions, producing a ripple effect, cycling at around 21-25 depressions per second.
The depressions are equal in amplitude (around 10 to 15 mbar).
An internal combustion engine acts as an air pump. It draws air in through the intake and forces it out through the exhaust. The rate at which the air mass enters the intake is the rate at which the air mass leaves the exhaust (unless it is added to or expelled via other means, such as leaks).
Air mass flow depends on engine speed, engine displacement, and intake manifold air density. Within the intake manifold volume, the air density depends on pressure. Therefore, if we use a throttle valve to regulate the intake manifold pressure, we can control the intake air density.
If engine speeds and throttle valve positions are known, we can use intake manifold pressure measurements to evaluate the air mass flow behaviour within an engine.
Please note: you should only make pressure value decisions based on comparison with manufacturer data.
Intake manifold pressure behaviour, during idling, can be described, as follows:
The intake manifold pressure reflects the net effect of all cylinder and intake interactions. The relationships are complex; for example, two valve-overlap scenarios occur around the start of every induction stroke:
Although a uniform pattern should be apparent, the intake manifold pressure waveform characteristics cannot be accurately predicted without exact knowledge of the engine design.
Therefore, diagnosis relies mostly on the identification of periodic anomalies within the waveform. An observed anomaly provides sufficient justification for further investigation.
We can link typical faults to possible waveform effects, for example:
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.
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