Single point injection - injector: current

The purpose of this test is to monitor the current from a Single Point injector to verify correct operation.

How to perform the test

View connection guidance notes.

1. Use the vehicle circuit diagram to identify the circuit functions.
2. Connect a low amp clamp to PicoScope Channel A.
3. Switch on and zero the clamp before connecting around the injector power supply circuit.
4. Start the engine and allow it to idle.
5. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
6. Start the scope to see live data.
7. With your waveform on screen stop the scope.
8. Turn off the engine.
9. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.

 Note:

The orientation of the current clamp relative to the wire will determine whether it has a positive or negative output. If a live waveform does not appear on your screen, or appears to be inverted, try reversing the orientation of the clamp.

Example waveform

Waveform notes

It can be clearly seen from the example waveform that the waveform is clearly split into two easily defined areas. The first part of the waveform is responsible for the electromagnetic force lifting the pintle. In this example the time taken is approximately 1.3 ms. At this point the current can be seen to be maintained at 1.3 amps before dropping to zero as the pintle closes. With this in mind it can be seen that the amount of time that the injector is held open is not necessarily the same as the time measured. It is not however possible to calculate the time taken for the injector's spring to fully close the injector and cut off the fuel flow.
This test is ideal for identifying an injector with an unacceptably slow solenoid reaction time. Such an injector would not deliver the required amount of fuel causing the engine to run lean and consequently the lambda sensor voltage will be affected.

Further guidance

The reason that a single point injector is used rather than a multi-point configuration is sometimes hard to justify, and can only be due to a consideration towards costing and ease of application. A single injector is used (on larger engines two injectors can be used) in what may appear to be a carburettor housing.
It has a very low operating pressure (usually around 1 bar) and the atomising of the fuel can only be described as minimal, relying on the air movement within the inlet manifold to break the fuel down into smaller particles, ready for combustion.

Due to its design the main advantage over a carburettor is that a lambda sensor can be employed ensuring that closed loop control is maintained. Multi-point will undoubtedly ensure that the vehicle's engine has a higher power output with less exhaust emissions.
Due to the design of the system, a conventional air flow meter cannot be used and a map sensor is often employed.

GT038