Fuel pressure regulator vacuum pulsation (ignition triggered) - idling

The purpose of this test is to observe vacuum operated fuel pressure regulator pulsations to determine injector activity.



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:

  1. switch off the ignition
  2. clean the HT leads
  3. inspect them for damage
  4. clip the HT pickup over the desired undamaged HT lead
  5. ensure all test leads are kept clear of hot or rotating parts before starting the engine


How to perform the test

View connection guidance notes.

  1. Disconnect the vacuum hose from the fuel rail pressure sensor and plug the hose.
  2. Connect the First Look Sensor into PicoScope channel A and use the hose size adaptor to connect onto the fuel rail pressure regulator vacuum port.
  3. 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.
  4. Start the engine and run at idle.
  5. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
  6. Start the scope to see live data.
  7. With your live waveforms on screen stop the scope.
  8. Stop the engine and ensure the ignition is off.
  9. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform . 

Example waveform

Waveform notes

This waveform was taken using secondary ignition number 1 as trigger on Channel B and the FirstLook sensor signal on Channel A. Let us consider what happens when an injector is opened, as it affects the regulator. The sudden drop in fuel pressure causes a fluctuation in the regulator. The fuel pump then compensates to fill the void left by the exiting fuel, thus returning the regulator to its starting position. In this test we can view the resulting waveform caused by this action. Notice the sharp change as the injector is opened followed by the compensation curve back to the base state.

The waveform displayed will depend on the injector firing order. In this case the injectors are sequential (each injector fires at a present time before the ignition). In the above example it can be seen that the drop in fuel pressure for number 4 cylinder is slightly less than the others, this may suggest a partially blocked injector. In order to identify the cylinder containing the offending injector, shift just over 360 degrees before the ignition spark.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select, Fuel pressure regulator 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)


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Guided test: Fuel pressure regulator vacuum pulsation (ignition triggered) - idling