Gasoline direct injection - injector voltage

The purpose of this test is to check the Gasoline Direct Injection (GDI) injector control voltages from an Engine Control Module (ECM).

How to perform the test

View connection guidance notes.

1. Use manufacturer's data to identify the positive feed and switched earth circuits.
2. Connect PicoScope Channel A to the injector positive feed circuit.
3. Connect PicoScope Channel B to the injector switched earth circuit.
4. Minimise the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
5. Run the engine.
6. Start the scope to see live data.
7. With your live waveforms on screen stop the scope.
8. Turn off the engine.
9. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.

Example waveform

Waveform notes

These known good waveforms have the following characteristics:

• When the injector is off, the ECM supplies 4 to 5 V to both sides of the injector circuit.
• The ECM switches on the injector by simultaneously supplying a boosted 40V, to the positive feed side Channel A, and a path to earth, 0 V, on the switched earth side Channel B.
• Once the injector valve is fully open, the boost voltage is removed and briefly reduces to 0 V, whilst the switched-earth voltage remains at 0 V.
• Within 0.1 to 0.2 ms, a pulsed, square wave, voltage is established on the positive feed to keep the injector valve open.
• The ECM switches off the injector by simultaneously providing a 4 to 5 V to both sides of the injector circuit.
• There is a peak in the switched earth voltage after the injector is switched off.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select Injector voltage.

Further guidance

A Gasoline Direct Injection (GDI) injector delivers fuel directly to the air charge within a cylinder.

GDI injector fast reaction times enable an engine management system to operate across different cylinder charge modes, for example:

• a homogenous air charge having the same stoichiometric air-fuel mixture throughout the combustion volume; or
• a heterogeneous air charge having a stratified air-fuel mixture with a small fuel rich volume within an overall lean combustion volume.

GDI injectors can deliver fuel with complex spray patterns and provide multiple injections per compression stroke. Furthermore, fuel can be kept from the cylinder volume until very close to the point of ignition reducing the risk of pre-ignition or knock and allowing the use of higher compression ratios, all of which leads to better thermal and fuel efficiencies.

As fuel injection coincides with the compression stroke, GDI injection pressures must be sufficient to overcome the in-cylinder pressures that occur across all engine load conditions. Therefore, GDI systems require a high pressure, up to 200 bar, fuel delivery system consisting of a common fuel rail supplied by a high-pressure fuel pump.

The ECM improves GDI injector response times by increasing the circuit voltage during the opening phase providing additional energy to move the valve rapidly. However, once the valve is fully open, only a relatively small voltage is necessary to hold it place, which the ECM maintains with a lower, pulsed, square-wave voltage.

GDI injector failures may cause loss of engine performance, misfire, or excessive smoking symptoms. Possible failure modes may be: 

• mechanical inlet or outlet blockages, sticky/stuck injector valves or defective spray patterns;
• electrical open or short circuits and high resistances in the wiring or solenoids; or
• internal ECM faults.

When operating out of their normal tolerances, for example repeated short runs or cold start operations, excessive soot may build up within the engine systems and cause a variety of secondary issues (e.g. blocked inlets, EGR valves, turbo vanes etc.). As such, regular maintenance is essential for continued operation within tolerances.

GT861-EN