The purpose of this test is to assess vacuum operated fuel pressure regulators to determine injector activity.
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:
Testing sensors and actuators (to include relevant circuit/connectors):
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.
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.
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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