Primary ignition vs injector current

The purpose of this test is to monitor the current draw from an injector whilst observing the primary ignition trace.

Connection guidance

Note: This helpfile refers to a 10:1 attenuator. If you are using a 20:1 attenuator please adjust the Probe settings for the relevant channel. These settings can be found under the Channel Options button, then: Probe > 20:1 Attenuator.

How to perform the test

Channel A

Plug the 10:1 attenuator into Channel A on the PicoScope and plug a BNC test lead into the attenuator. Placing a large black clip on the test lead with the black moulding (negative) and a Back-pinning or multimeter probe onto the test lead with the colored moulding (positive). Place the black clip onto the battery negative terminal and probe the coil's negative (or number 1) terminal with the Back-pinning or multimeter probe as illustrated in Figure 1.

The example waveform shows that the voltage seen during this test is relatively high and the scaling of the oscilloscope is therefore adjusted to suit. It is important that the 10:1 attenuator is used in all situations when a voltage exceeding 200 volts is to be measured.

Channel B

Connect the low-amp current clamp to Channel B of the PicoScope. Select the 20 A 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.

Alternatively the TA012 breakout lead can be used. Place the low-amp clamp on either the blue or the yellow exposed cable section of the lead, as illustrated in Figure 2. As there is no consistency to which terminal carries the supply, it may be necessary to observe both waveforms and select the correct one.

With the example waveform displayed on the screen you can now hit the space bar to start looking at live readings.

Example waveform

Waveform notes

In this waveform we can observe the current drawn by the injector (shown in red) at the same time as monitoring the primary ignition trace (shown in blue). The main reason for evaluating these two waveforms together is to identify the cause of a non-start situation or sudden loss of power, causing the engine to stop. If the primary trace is absent, there will be no switching of the injectors as these two circuits are timed together while the loss of the injector current signifies that a fault has occurred within the injection circuit.

The frequency of the injection trace when compared to the primary signal will differ between sequential and simultaneous injection. Sequential having one pulse per 720, while simultaneous will predominantly have two. Some simultaneous systems do however have a single pulse, but these are in the minority.

Further guidance

Please see individual waveform topics:

  • Ignition primary
  • Multi-point injector current


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

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


  • Premium 6-way breakout lead set


  • Back-pinning Probe Set


  • Flexible Back-pinning Probe


  • Large Dolphin/Gator Clips


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Guided test: Primary ignition vs injector current