PD (unit) injector (using a low-current clamp and two BNC leads)

You will require a PicoScope to perform this test. A list of suitable accessories can be found at the bottom of this page.

    To avoid damage to your scope, you may need to use an attenuator for this test. These instructions do not refer to an attenuator as it is based on either PicoScope 4423 or PicoScope 4425 automotive scopes.

If you are using a previous PicoScope Automotive model, you will need either a 10:1 or 20:1 attenuator and will need to adjust the Probe settings for the relevant channel. These settings can be found under the Channel Options button, then:

• Probe > 10:1 Attenuator
• Probe > 20:1 Attenuator

How to perform the test

Locating the wiring loom multi-plug

The wiring loom for the injectors can be accessed at the round multi-plug at the rear of the cylinder head. It may be necessary to remove the multi-plug by releasing the locking pin and then carefully stripping back the loom insulation to expose adequate wire to make the connections. Refit the multi-plug and repair the loom insulation once the tests have been concluded.

Channel A

Plug the current clamp into Channel A of the scope. Set the clamp to the 20 amp setting if required and auto-zero it. Place the clamp around the positive wire of the injector to be tested - it may be necessary to refer to a manufacturer's wiring diagram.

Channel B

Plug a BNC-to-4 mm test lead into Channel B of the scope. Connect an acupuncture probe to the positive (colored) connection of the test lead. Place a black clip on the negative connection (black) and clip it to a suitable earth connection in the engine bay. Probe the common positive wire of the injectors - it may be necessary to refer to a manufacturer's wiring diagram.

Channel C

Plug a BNC-to-4 mm test lead into Channel C of the scope. Connect an acupuncture probe to the positive (colored) connection of the test lead. Place a black clip on the negative connection (black) and clip it to a suitable earth connection in the engine bay. Probe the negative wire of the injector to be tested - it may be necessary to refer to a manufacturer's wiring diagram.

The connections are illustrated in Figure 1.

Example waveform

Waveform notes

Channel A

This shows the injector current. At the point of injection the current rises from zero to around 15 amps where there is a brief interruption before continuing to rise to just over 17.5 amps. The injection current remains high for a short period before reducing to about 11 amps and then enters a multi-pulsing phase.

Channel B

This shows the injector live circuit. It is important to note that the injectors are live switched; at the start point of injection the normal battery supply voltage is shown at around 14 V. The supply voltage is modulated to create the injection phases throughout the injector duration of around 2 ms.

Channel C

This shows the injector earth circuit. At the end of the injection period the voltage in the injector's electromagnetic windings collapses and this induced voltage can be seen rising to around 50 volts.

Technical information

The electromechanical unit injectors are located inside 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 on the injectors to compress the fuel, so there is no high-pressure pump. This action generates between 1,800 and 2,050 bar of pressure.

This system is referred to by the Volkswagen Audi Group as Pumpe-Düse (PD).

Bosch Unit Injector

Figure 2

The electrical control also differs from common-rail as the supply voltage is at normal battery voltage. The switching of the injections is conducted by the positive supply and not by controlling the earth path.

As with all modern injectors there is a pilot and main injection phase to control noise and emissions and maintain a smooth combustion. The rise of the injector current from zero to the maximum is the pilot injector period. The period of the multi-pulsing current is the main injection phase.

Figure 2 shows a Bosch Unit Injecotr, as used on 1.4, 1.9 or 2.5 VWG engines.

AT385-1

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

  • 30 A (low amps) current clamp

    £259.00

  • 20 A / 60 A DC (low amps) current clamp

    £159.00

  • Back-pinning Probe Set

    £48.00

  • Flexible Back-pinning Probe

    £7.00

  • PicoScope Battery Clip

    £5.00

  • Large Dolphin/Gator Clips

    £10.00

  • Premium Test Lead: BNC to 4 mm, 3 m

    £48.00

  • Premium Test Leads: Set of four leads 3 m (TA125 - TA128)

    £179.00

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Guided test: VAG PD (current, voltage and earth)