Single point injection - injector: current

The purpose of this test is to evaluate the correct operation of a Single Point Injection (SPI) injector based on current flow, response, and formation during engine run conditions.

Connection guidance

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:

  1. Breakout leads.
  2. Back-pinning probes.

Testing sensors and actuators (to include relevant circuit/connectors):

  • When testing a sensor, it is desirable to gain access at the control unit.
  • When testing an actuator, it is desirable to gain access at the actuator.

How to perform the test

Plug the current clamp into Channel A on the PicoScope. Select the 20A range if required and switch the current clamp on. Press the zero button before connecting the clamp to the circuit.

The current clamp should be placed onto the fuel injector's supply wire, as illustrated in Figure 1.

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.


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


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


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Guided test: Single point injection - injector: current