Saturated Injector

Automotive Sensors

Communication Systems

Ignition Systems

Others

Diesel Systems

General description

Injectors are electrically operated valves which accurately control the quantity of fuel delivered. By adding the fuel to the air sucked in by the engine, a mixture is created with the required fuel/air ratio.
Most electronic fuel injection (EFI) systems use an ECU with 12 volt saturated circuit drivers. These systems are very inexpensive, simple, and reliable. This type of driver works by supplying 12 volts to the injectors and the ECU turns it on and off to establish a fuel injector pulse. Saturated injectors are generally higher impedance than peak and hold, running in about the 10-16 ohms range.
The new technology used in the design and construction of today’s high impedance injectors allows much larger flow rates, much better response times, and much more predictable low pulse width operation than previous designs – all without overheating. This means that low impedance injectors are no longer the peak of performance when considering fuel injectors.

Appearance

Fig. 1 Typical saturated injector

Principle of operation of the saturated injectors

A saturated signal is a simple signal used to operate high impedance injectors. A single intensity signal is sent to a fuel injector which causes the valve to open and remain open until the signal has ended. Unlike peak/hold, a saturated injector remains "on" for the entire pulse width. This means that the current flow in the driver and injector circuit stays low keeping the components cool for long life. Advantage of this design is the reduced heat. The downside to a Saturated Circuit driver is that it has a slower response time (opening and closing time) than a peak and hold type. This slower time can somewhat decrease the usable operating range of the injector energized by this driver. An injector operating on a saturated circuit driver typically has a reaction time of 2 milliseconds while a peak and hold driver typically responds in 1.5 milliseconds. Another disadvantage of this design is that the saturated injectors can't handle large CC or lb/hr styles due to limitations in its speed.

Possible damage to the injectors:

  • Open circuit or short to positive or to ground in wire(s);
  • No or poor plug connection conduction;
  • Ground connection is loose or corroded;
  • Mechanical fault in component.

CHECK RESISTANCE

  1. Make sure ignition is off and the engine is not started;
  2. Disconnect the two-pin injector connector;
  3. Connect a precise ohmmeter between the terminals of the injector connector. Resistance must be between 10 and 16 ohms;
  4. Plug in the injector connector.

TESTING THE OUTPUT SIGNAL WITH OSCILLOSCOPE

Injector Voltage vs Current

1. Channel A:

Plug the 10:1 Attenuator to channel A of the CarScope and connect a BNC test lead to the attenuator. Connect the red test lead to one of the injector wires and the black crocodile lead to the chassis ground.

2. Channel B:

Connect the CA-60 AC/DC current clamp to channel B.

Range ±20A

Clamp switch should be in 1mV/10mA position.

Switch the current clamp on, press the ZERO button before connecting the clamp to the circuit.

It is important to note that only one of the two wires have to be clamped, and not both of them. It doesn’t matter which cable is clipped with the current clamp: the positive or the negative one. This will only affect the polarity of the measured current. But incorrect connection will lead a reading of incorrect polarity. The clamp arrow matches the injector current direction.

Note: the CA-60A probe is supplied with a 4 mm banana plug type connectors so it cannot be plugged directly to a CarScope Pro oscilloscope. A banana plug to BNC adapter must be used to connect the current clamp to the oscilloscope.

Note: When performing a DC current measurement, always push the ZERO button on the clamp until the CarScope displays a zero line.

Important note: Only one of the two wires should be clamped, and not both of them. It doesn’t matter which wire will be clipped with the current clamp: the positive or the negative one. This will only affect the polarity of the measured current.

3. Start the engine, warm it to operating temperature and leave it idling.

4. Compare result with the waveform in fig. 2.

Fig. 2

Note: The test set-up may distort the recorded signals slightly.

Injector Voltage

1. Channel A:

Plug the 10:1 Attenuator to channel A of the CarScope and connect a BNC test lead to the attenuator. Connect the red test lead to one of the injector wires and the black crocodile lead to the chassis ground.

2. Channel B:

Plug the 10:1 Attenuator to channel B of the CarScope and connect a BNC test lead to the attenuator. Connect the red test lead to one of the injector wires and the black crocodile lead to the chassis ground.

3. Channel C:

Plug the 10:1 Attenuator to channel C of the CarScope Pro/LAN/Plus and connect a BNC test lead to the attenuator. Connect the red test lead to one of the injector wires and the black crocodile lead to the chassis ground.

4. Channel D:

Plug the 10:1 Attenuator to channel D of the CarScope Pro/LAN/Plus and connect a BNC test lead to the attenuator. Connect the red test lead to one of the injector wires and the black crocodile lead to the chassis ground.

5. Start the engine, warm it to operating temperature and leave it idling

6. Compare result for each injector with the waveform in fig.3

Fig.3

 

 

 

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