The Bosch Motronic MP3.2 system is a sequential multipoint fuel injection system whereby all injectors sequentially inject fuel directly into the cylinders and once per engine cycle.
Fuel injectors
fuel injectors (see illustration 11.36) have electromagnetic control. The electronic control unit drives the injectors. The voltage to the injectors comes from the main relay. The duration of the nozzle opening is between 1.5 and 10 milliseconds. The duration of fuel injection depends on engine temperature, engine load, engine speed and operating conditions.
11.36 Fuel injector
When the solenoid valve closes, a reverse electromagnetic field voltage of up to 60 volts is created.
Nozzle voltage values
Terminal numbers
See illustration 11.37
11.37 Wiring diagram for fuel injectors
Nozzle resistance values
Terminal numbers
Nozzle Duty Cycle Table
Nozzle type
Sequential fuel injection
Influence of external factors
- Vacuum leaks
- Ignition system malfunction
- Air filter clogged
- Engine oil contaminated
- Fuel Tank Ventilation Malfunction
Checking the injectors (general check)
1. Inspect the injector multi-pin connectors for signs of corrosion or damage.
2. Make sure the pins on the multi-pin connector are properly installed and making good contact with the injectors.
3. Check for corrosion at the relay and injector terminals, and at the ECU and injector terminals. Corrosion on the terminals is the cause of poor injector performance.
Checking the performance of the injector using an oscilloscope or a meter for the duration of the closed state of the breaker contacts
1. Two wires are routed to the injector multi-pin connector: a power wire and a signal wire.
2. Peel back the rubber insulation (where possible) to the multi-pin connector of the injector, remove the protective cover or connect the outlet block (WWII) between the multi-pin connector of the electronic control unit and the electronic control unit.
3. Connect the negative lead of an oscilloscope or breaker closed time meter to ground on the motor.
4. Connect the positive probe of an oscilloscope or a meter for the duration of the closed state of the breaker contacts to terminal No. 1 of the signal wire of the injector. Since the injectors inject fuel sequentially, they should be checked individually. Note. The indication of the duration meter of the closed state of the breaker contacts will be received only on the wire connecting the nozzle to the electronic control unit. If it is not possible to get a reading, then connect the probe to another terminal and repeat the test.
Checks with the engine off
1. Turn the crankshaft.
2. The instrument will display either a waveform or duty cycle reading (pulse duration). If the device can measure readings in milliseconds, then this is the most successful measurement (see illustration 5.38)
3. Measure the pulse frequency. After a few seconds of turning the crankshaft, the initial value should decrease.
Clear waveform or sufficient signal
1. There are three main points to consider:
- Does the waveform match the pattern?
- Is the pulse signal length appropriate for the temperature?
- Does the frequency of the pulse increase for a few seconds when cranking the crankshaft?
2. If the answer to all three questions is - «Yes», then the cause of the engine not starting is unlikely to be related to the fuel injection system. However, a fuel pressure test should be performed.
3. If the ignition coil primary signal is sufficient, then the fault is unlikely to be related to the electronic control unit.
Fuzzy or no waveform or no signal
1. Check the duration of opening of other nozzles.
2. Check for sufficient signal from the crankshaft angle sensor.
3. Check the voltage supply to the injector multi-pin connector.
4. If there is no voltage, check the resistance of the injector and the voltage supply to the injector.
Note. If the oscilloscope shows voltage at the nominal voltage of the battery, but there is no waveform, then voltage is supplied to the injector, but the circuit does not turn on.
5. Disconnect the multi-pin connector of the electronic control unit (see warning #3).
6. Turn on the ignition.
7. Using a jumper wire, very quickly touch each injector pin in the ECU multi-pin connector to ground.
8. If the nozzle fires, then check the voltage supply to the electronic control unit and its grounding. If the voltage supply and grounding are in order, then the electronic control unit may be faulty.
9. If the injector does not fire, check for battery voltage at the ECU pin.
10. If voltage is present, the injector may be defective.
11. If there is no voltage, check the continuity of the electrical wiring going between the multi-pin connectors of the injector and the multi-pin connector of the electronic control unit.
A Pulse duration that is too long or too short
1. Check the coolant temperature sensor (CTS).
2. Check the intake manifold absolute pressure sensor (IDA).
Note. If the ECM was using LOS mode due to one of the sensors failing, the engine may run properly while it is warm. However, it may be difficult to start the engine from a cold state.
Checks with the engine running
1. Run the engine at various speeds. Record the values obtained at the following engine speeds.
- idle speed
- At 2000 rpm
- At 3000 rpm
- Slow throttle opening Fast throttle opening
- When braking: increase the engine speed to approximately 3000 rpm and release the throttle.
2. Make sure that the pulse duration from each injector is similar to the pulse duration from other cylinders (within 0.1 ms).
3. Compare the results with the values specified in the specifications, both on a cold and warm running engine.
4. Pulse duration as a percentage (%) should increase as the engine speed increases.
5. The duration of the pulse in ms should not change significantly with a gradual increase in engine speed.
6. When accelerating, the pulse duration should increase.
7. When braking, when the engine is warm, the oscilloscope should not display the pulse width, or it should fall to zero (digital measuring instrument) and reappear when the engine speed is less than 1200 rpm.
8. If the value of the device does not drop to zero, then check the correct adjustment of the throttle valve and the performance of the throttle position sensor (TPS).
9. Noise from the injectors should also temporarily disappear as the fuel cut-off valve will operate.
A Pulse duration that is too long or too short
1. Check the coolant temperature sensor (CTS).
2. Check the intake manifold absolute pressure sensor (IDA).
Note. If the ECM was using LOS mode due to one of the sensors failing, the engine may run properly while it is warm. However, it may be difficult to start the engine from a cold state.
Resistance Tests
- Remove the injector multi-pin connectors and measure the injector resistance between the two terminals.