Multi-point injector - voltage and current

The purpose of this test is to monitor the injector voltage and current to determine the integrity of the injector circuit and the operation of the injector.

Connection guidance

Connection for diagnostic work will vary dependent on application.

Technicians should wherever 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 module.
  • When testing an actuator, it is desirable to gain access at the actuator.
   

To avoid damage to your scope, you may need to use an attenuator for this test.

These instructions do not refer to an attenuator as it is based on our PicoScope 4425 automotive scope.

If you are using a previous PicoScope Automotive model, you will need either a 10:1 or 20:1 attenuator and will need to adjust the Probe settings for the relevant channel.

These settings can be found under Channel Options, then:
• Probe > 10:1 Attenuator
• Probe > 20:1 Attenuator

How to perform the test

  1. Connect the injector breakout lead TA012 onto the injector.
  2. Connect PicoScope Channel A to the injector power supply at the breakout lead.
  3. Connect the low amp current clamp into Channel B on your PicoScope, select the 20 amp scale, switch on and zero the current clamp.
  4. Attach the current clamp onto the breakout lead, injector supply circuit.
  5. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
  6. Run the engine.
  7. Select GO or press the space bar to see live data.
  8. Turn off the engine.
  9. Use the WAVEFORM BUFFER and ZOOM tools to examine your waveform.

Example waveform

Waveform notes

Initially, the waveform voltage on the switched-earth side of the injector is at battery positive voltage (around 13-15 volts) and no current flows around the injector circuit.

When the engine control module (ECM) provides an earth path to the battery negative voltage (0 volts), the injector valve starts to open and current begins to flow. This marks the start of injection.

The circuit current ramps-up in two phases, with the change between the two occurring about 1.25ms after the start of injection. The change point marks when the injector valve is open fully.

Both the injector voltage and current show that the injection duration is about 4.25ms. Within this time, at around 2.5ms after the start of injection, the circuit current reaches its peak value, which is sustained by the ECM for the remainder of the injection period.

When the ECM removes the earth path to the injector circuit (at 4.25ms), the current flow stops and the injector valve starts to close. At this point, there is a peak (spike) in the waveform voltage reaching up to around 80 volts.

Within one milli-second of the injector being switched off and as the waveform voltage decays from its peak, there is a slow-down in the decay rate followed by a rapid resumption of the initial decay rate: this ‘hump’ in the waveform voltage indicates the normal closing behaviour of the injector valve.

The waveform voltage remains at battery positive volts until the next start of injection (switch to earth).

Waveform Library

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

Further guidance

The function of an (indirect) injector in a multi-point injection system is to deliver the correct quantity of atomised fuel to the air in the inlet tract, as it is drawn through to a cylinder.

On these systems, there is one injector per cylinder, but all injectors are supplied by a shared (common) fuel rail. As the fuel rail pressure regulator maintains a constant pressure differential between an injector’s fuel inlet and its outlet to the manifold, the ECM only needs to adjust the injection duration to control the delivered fuel quantity.

Typically, the ECM uses input signals from the coolant and intake-air temperature sensors, a manifold air pressure (MAP) sensor and/or air-flow meter (AFM) sensor, and the accelerator and throttle position sensors, etc. to calculate the required fuel quantity. For example, when a cold engine is started the ECM increases the injection duration to counter the effects of cold-starting, but then decreases the injection duration as the engine reaches its normal operating temperature.

Indirect-injection fuel injectors commonly have solenoid-controlled valves, which work against a spring force acting to close them. As such, the solenoid must be energised with a current flowing through it for the valve to open. If the solenoid is not sufficiently energised the valve will not open fully.

Typically, an injector circuit has a constant battery feed (which may be shared with the other injectors), supplied from a relay or control module, and a switched-earth (to battery negative), controlled by the ECM (or separate injection control module).

When current flows through them, solenoids build and store energy in their electromagnetic field. When the current flow stops, the solenoid's electromagnetic field collapses, producing a large but brief electromagnetic force in the direction opposite to the original current flow (i.e. a back-emf). The back-emf is visible as a large voltage spike in an injector’s switched-earth voltage waveform.

The peak back-emf voltage will vary from vehicle to vehicle; some injector circuits include a Zener diode or a resistor-capacitor combination that acts to limit the peak back-emf voltage (for example, it might be 'squared-off').

The ‘hump’ observed in an injector’s back-emf spike occurs because the valve spring forces the injector valve to move rapidly back to its closed position, which disturbs the solenoid's collapsing electromagnetic field. This waveform feature is an important diagnostic aid: if it is missing, it can be assumed that the valve is not moving properly.

There are two types of multi-point injection systems:

Sequential systems fire one injection pulse per engine cycle (720° of crankshaft rotation) in time to coincide with the opening of the inlet valve.

Simultaneous systems fire all the injectors within one bank at the same time (i.e. all the injectors in an inline engine arrangement, or each bank of injectors in a ’V’ arrangement), twice per engine cycle. In these systems, less fuel is required per injection, therefore the injection durations are reduced in comparison to sequentially firing systems (e.g. to about 2.5ms).

Diagnostic trouble codes

P0200 – Injector Circuit Malfunction

P0201 – Injector Circuit Malfunction – Cylinder 1

P0202 – Injector Circuit Malfunction – Cylinder 2

P0203 – Injector Circuit Malfunction – Cylinder 3

P0204 – Injector Circuit Malfunction – Cylinder 4

P0205 – Injector Circuit Malfunction – Cylinder 5

P0206 – Injector Circuit Malfunction – Cylinder 6

P0207 – Injector Circuit Malfunction – Cylinder 7

P0208 – Injector Circuit Malfunction – Cylinder 8

P0209 – Injector Circuit Malfunction – Cylinder 9

P0210 – Injector Circuit Malfunction – Cylinder 10

P0211 – Injector Circuit Malfunction – Cylinder 11

P0212 – Injector Circuit Malfunction – Cylinder 12

P0213 – Cold Start Injector 1 Malfunction

P0214 – Cold Start Injector 2 Malfunction

P0216 – Injection Timing Control Circuit Malfunction

P020A – Cylinder 1 Injection Timing

P020B – Cylinder 2 Injection Timing

P020C – Cylinder 3 Injection Timing

P020D – Cylinder 4 Injection Timing

P020E – Cylinder 5 Injection Timing

P020F – Cylinder 6 Injection Timing

P021A – Cylinder 7 Injection Timing

P021B – Cylinder 8 Injection Timing

P021C – Cylinder 9 Injection Timing

P021D – Cylinder 10 Injection Timing

P021E – Cylinder 11 Injection Timing

P021F – Cylinder 12 Injection Timing

P0261 – Cylinder 1 Injector Circuit Low

P0262 – Cylinder 1 Injector Circuit High

P0263 – Cylinder 1 Contribution/Balance Fault

P0264 – Cylinder 2 Injector Circuit Low

P0265 – Cylinder 2 Injector Circuit High

P0266 – Cylinder 2 Contribution/Balance Fault

P0267 – Cylinder 3 Injector Circuit Low

P0268 – Cylinder 3 Injector Circuit High

P0269 – Cylinder 3 Contribution/Balance Fault

P0270 – Cylinder 4 Injector Circuit Low

P0271 – Cylinder 4 Injector Circuit High

P0272 – Cylinder 4 Contribution/Balance Fault

P0273 – Cylinder 5 Injector Circuit Low

P0274 – Cylinder 5 Injector Circuit High

P0275 – Cylinder 5 Contribution/Balance Fault

P0276 – Cylinder 6 Injector Circuit Low

P0277 – Cylinder 6 Injector Circuit High

P0278 – Cylinder 6 Contribution/Balance Fault

P0279 – Cylinder 7 Injector Circuit Low

P0280 – Cylinder 7 Injector Circuit High

P0281 – Cylinder 7 Contribution/Balance Fault

P0282 – Cylinder 8 Injector Circuit Low

P0283 – Cylinder 8 Injector Circuit High

P0284 – Cylinder 8 Contribution/Balance Fault

P0285 – Cylinder 9 Injector Circuit Low

P0286 – Cylinder 9 Injector Circuit High

P0287 – Cylinder 9 Contribution/Balance Fault

P0288 – Cylinder 10 Injector Circuit Low

P0289 – Cylinder 10 Injector Circuit High

P0290 – Cylinder 10 Contribution/Balance Fault

P0291 – Cylinder 11 Injector Circuit Low

P0292 – Cylinder 11 Injector Circuit High

P0293 – Cylinder 11 Contribution/Balance Fault

P0294 – Cylinder 12 Injector Circuit Low

P0295 – Cylinder 12 Injector Circuit High

P0296 – Cylinder 12 Contribution/Balance Fault

GT388-2

Disclaimer
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

    £259.00

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

    £159.00

  • 2 Pin AMP connector breakout lead

    £30.00

  • Back-pinning Probe Set

    £48.00

  • Flexible Back-pinning Probe

    £4.25

  • PicoScope Battery Clip

    £2.75

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Guided test: Multi-point injector - voltage and current