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.

Connection guidance

Connection for diagnostic work will vary dependent on application.

Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.

General connection advice

PicoScope offers a range of options within the test kits.

Dependent on difficulty of access, choose from:

  1. Breakout leads.
  2. Back-pinning probes.

Testing sensors and actuators (to include relevant circuit/connectors):

  • When testing a sensor, it is desirable to gain access at the control module.
  • When testing an actuator, it is desirable to gain access at the actuator.

How to perform the test

   

WARNING

Uninsulated HT pickups are designed to clip around double-insulated HT cables only – they are not designed for direct connection to a hazardous live voltage. To prevent injury or death, switch off the engine and secure against restart. Clean and inspect the HT lead for damage to insulation and fit only to undamaged fully insulated leads. Ensure that leads are safely clear of hot and / or rotating parts. The engine can now be restarted for the test duration.

Note;

Disable the vehicle fuel system before testing.

  1. Connect the First Look sensor to a vacuum source at the intake manifold and to channel A of your PicoScope.
  2. With the ignition off, connect a secondary ignition pick up around the HT lead for cylinder number 1 and to PicoScope channel B. Ensure the secondary pick up has a good earth.
  3. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
  4. Start the scope to see live data.
  5. With the fuel system disabled to prevent starting crank the engine to generate your waveforms.
  6. With your waveforms on screen stop the scope.
  7. Use the Waveform Buffer and Zoom tools to examine your waveform.

Note;

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.

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.

GT131-2

Disclaimer
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

    £449.00

  • Secondary ignition pickup (capacitive with BNC)

    £58.00

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2 comments | Add comment

MikeW
November 20 2018

Hi Anthony, thank you for your observation. Test amended.

Anthony
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