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):
Warning: When attaching or removing secondary ignition pickups from damaged HT leads there is a danger of electric shock. To eliminate this possibility, switch off the ignition before attaching or removing the secondary igntion pickup.
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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June 01 2016
To make things simple I connected my WPS500X to the Schrader Valve on the Fuel Rail and used the ignition paddle on the fuel injector. This saves me from guessing which injector caused which drop by moving the paddle to the next coil until you have the offender. I had a weeker injector but it was with a 0.7psi deviation from the best injector within limits (max. 1.5psi)
October 11 2015
Looking at the trace it looks like cylinder #4 is the one with blocked injector.
Injection on a 4 stroke with a fully sequential injection system starts close to TDC at the end of exhaust/start of intake stroke; ie. to identify the cylinder shift from just over 360 degrees from ignition spark.