The purpose of this test is to check a PD injector current draw under different operating conditions non intrusively.
Note: This waveform has been set up in Auto trigger mode, with a rising-edge trigger. If the waveform does not start with a positive pulse, the current clamp has been connected the wrong way round. Remove it and replace facing the opposite direction.
These example waveforms show the injector current under different operating conditions.
Example 1: The first injector phase is pre-injection and the second is the main injector phase.
Example 2: As the engine speed is raised, the control module increases the duration of the main injector phase.
Example 3: On overrun, only the pre-injection phase remains.
The piezo-mechanical unit injectors are located in the cylinder head and the wiring runs through a circular multi-plug at the rear of the head to the individual injectors. The injectors are unlike common-rail injectors in that the high fuel pressure is generated by an additional rocker-arm running from the camshaft and acting directly onto the injectors. There is no high-pressure pump the injectors can operate across a wide range of pressures from 130 to 2,200 bar.
This system is referred to by the Volkswagen Audi group as Pumpe-Düse (PD).
There may be up to five injection phases:
Piezo injectors have a major advantage over conventional electromagnetic injectors, a very quick reaction time up to four times faster.
Piezo injectors contain a stack of about 300 thin ceramic plates. When the switching voltage is applied the plates expand and open the nozzle needle allowing fuel into the cylinder.
Figure 3 shows a piezo element in its two different states. Illustration 1 shows the stack with no supply voltage and illustration 2 shows the increase in height of the stack when the supply voltage is switched on.
Note; Once the stack is in the injector open position, it does not need to have a continuous supply voltage and remains in the open state until the close command. The open and close commands are the positive and negative current spikes in the waveform. For this reason, never disconnect the injector multi-plug with the engine running. If the injector is in the open state it could hydraulic-lock the engine with diesel fuel.
The engine will cut out if the control module detects any faults with the injectors or driver circuit.
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.
We know that our PicoScope users are clever and creative and we’d love to receive your ideas for improvement on this test. Click the Add comment button to leave your feedback.