Single point injection - injector: voltage [20:1 attenuation]

The purpose of this test is to evaluate the operation of a Single Point Injection (SPI) injector based on the switching voltage, pulse width, and formation during engine run conditions.

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

How to perform the test

View connection guidance notes.

1. Use the vehicle circuit diagram to identify the circuit functions.
2. Connect a 20:1 attenuator to PicoScope Channel A.
3. Connect Channel A to the injector signal 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.

Example waveform

Waveform notes

Single Point Injector (SPI) is also sometimes referred to as Throttle Body Injection (TBI).

A single injector is used (on larger engines two injectors can be used) in what may have the outward appearance of a carburettor housing.

The resultant waveform from the SPI system will show an initial injection period followed by multi-pulsing of the injector in the remainder of the trace. This section of the waveform is called the supplementary duration and is the only part of the injection trace to expand.

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 fewer exhaust emissions.

Due to the design of the system, a conventional air flow meter cannot be used and a map sensor is often employed.

GT037