Intake manifold pulsation (ignition triggered) - cranking

The purpose of this test is to assess the intake air and valve system for cylinder-specific defects on the intake side of the engine using the FirstLook sensor.

How to perform the test

Connect the First Look Sensor to Channel A on the PicoScope using the 25 ft BNC to BNC cable as shown in Figure 1, then attach the sensor to a vacuum source on the intake manifold (use the reducer hose if necessary) as shown in Figure 2.

Now connect the Secondary Ignition pick-up Lead to Channel B of the scope and attach the clamp to the cylinder 1 plug lead. Once you have disabled the fuel system (may not be possible on a carburated engine), crank the engine until the display pattern stabilizes. You can adjust the timebase and voltage scales to achieve best signal display.

This test is useful in the assessment of the intake air and valve system for cylinder specific defects on the intake side of the engine.

Example waveform

Waveform notes

This waveform shows a consistent signal pattern on Channel A as triggered against Channel B on the same time line. Cursor lines are added to show trigger reference (sparkplug 1) and show the time between trigger events. We can use this information to determine the approximate cranking speed of this engine.

Waveforms will vary from vehicle to vehicle, but should be consistent from cylinder to cylinder. Any variation suggests that one cylinder is drawing in a different amount of air/fuel mixture than the others.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select, Intake manifold pressure waveform.


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.

Suitable accessories

  • FirstLook Engine Diagnostic Sensor


  • Secondary ignition pickup (capacitive with BNC)


  • WPS500X Pressure Transducer Kit (with carry case)


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1 comment | Add comment

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.

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Guided test: Intake manifold pulsation (ignition triggered) - cranking