The purpose of this test is to investigate the operation of a digital Manifold Air Pressure (MAP) sensor under varied engine operating conditions.
The output from the external MAP sensor will show a square wave its frequency will be lower at idle than when the throttle is opened. The example waveform clearly demonstrates the output signal and when the frequency is also displayed can be compared against the model specification.
A higher frequency could result from any number of problems, but could be as simple as a split vacuum hose or incorrectly adjusted tappet clearances. Prolonged exposure to this higher frequency can result in damage to the catalytic converter.
The MAP sensor is employed to measure the pressure in the inlet manifold, and it is this output that when sent back into the engine management system can determine either the fueling or the amount of vacuum, light load ignition advance. The MAP sensor will in most cases measure a negative pressure, but can also be used to measure a positive boost pressure on a vehicle equipped with a turbo charger.
The sensor is a 3 wire device that will have:
This particular component can be either an integral part of the ECM or an individual component.
A digital map sensor will produce a square wave signal to the ECM, this square wave will change frequency with varying engine vacuum readings.
Typical readings whilst testing a MAP Sensor:
|Vacuum (inches Hg)||Vacuum (mbar)||Frequency (Hz)|
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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