The purpose of this test is to assess the engine condition during cranking by using the FirstLook™ sensor to observe intake manifold pulsation.
Uninsulated HT pickups are designed to clip around double-insulated HT leads only – they are not designed for direct connection to a hazardous live voltage.
To prevent injury or death, when connecting or disconnecting an HT pickup:
Some Engine Control Modules (ECM's) will operate the throttle independent to pedal operation whilst attempting to start. This will alter your waveform. If this is the case you will need to disconnect the throttle body connector and re-test.
These known good waveforms have the following characteristics:
The FirstLook™ sensor contains a piezo crystal device which converts pressure pulsations to a voltage signal output. The output can be taken as an indication of the underlying physical actions causing the pressure pulsations.
We check for potential engine issues by examining the intake manifold pressure pulsations. Specifically, we can compare intra-cylinder variations by looking at the effects of each of their respective inlet valve opening events.
The intake pulsations should have the following features:
Any waveform showing periodically occurring anomalies, for example a missing trough every 4 x intake events (with a 4 cylinder engine), will warrant further investigation.
The process for cylinder identification with an intake manifold pressure pulsation waveform is:
Causes of waveform anomalies
Intake-related faults which may cause waveform anomalies are:
Other engine faults also may affect the waveform:
Exhaust valvetrain issues (e.g. those listed for the intake valvetrain above).
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November 20 2018
Hi Anthony, thank you for your observation. Test amended.
May 01 2017
Disconnect electronic throttle body, newer vehicles will play with the throttle during cranking to try and start the vehicle. This will mess up a pattern as the throttle is opening and closing during test drastically changing manifold vacuum.