The purpose of this test is to evaluate the intake manifold pressures of a naturally aspirated gasoline engine during an engine snap test 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.
The pressure is around -700 to -720 mbar when the engine is stabilised at its idle speed.
There is a hash on the waveform.
The pressure rapidly rises to 0 bar when the throttle is snapped open.
The waveform hash increases with increasing engine speed.
The pressure remains at 0 bar whilst the throttle is held open.
The pressure rapidly decreases when the throttle is snapped shut.
The pressure drops to around -850 to -900 mbar with the throttle closed on overrun.
The pressure returns to around -700 to -720 mbar as the engine returns to a stable idle.
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).
We can use a snap test to see how the intake manifold pressure responds to a rapid change of throttle position from fully closed to fully open and back again. It tells us how well air can move through the engine.
Intake manifold pressure behaviour, during a snap test, can be described, as follows:
A snap test reveals broader trends in the overall intake manifold pressure behaviour. Please note that you should only make pressure value decisions based on comparison with manufacturer data.
The waveform may be affected by possible faults in the following ways:
Reduced intake manifold pressures, as caused by:
Increased intake manifold pressures, as caused by:
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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