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For 1990-2009 cars only
Makes 🢒 Saturn 🢒 2008 🢒 Astra 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Fuel Injector Diagnosis

Diagnostic Instructions
    •  Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    •  Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

The control module enables the appropriate fuel injector pulse for each cylinder. The ignition voltage is supplied directly to the fuel injectors. The control module controls each fuel injector by grounding the control circuit via a solid state device called a driver. A fuel injector coil winding resistance that is too high or too low will affect the engine driveability. A fuel injector control circuit DTC may not set, but a misfire may be apparent. The fuel injector coil windings are affected by temperature. The resistance of the fuel injector coil windings will increase as the temperature of the fuel injector increases.

When performing the fuel injector balance test, the scan tool is first used to energize the fuel pump. The fuel injector tester is then used to pulse each injector for a precise amount of time, allowing a measured amount of the fuel to be injected. This causes a drop in the system fuel pressure that can be recorded and used to compare each injector.

Diagnostic Aids
    • Operating the vehicle over a wide temperature range may help isolate the fuel injector that is causing the condition.
    • Perform the fuel injector coil test within the conditions of the customer's concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Special Tools

    • CH-48027-100 Digital Pressure Gage
    • SA9182E Electronic Fuel Injector Tester

Component Testing

Fuel Injector Coil Test

Verify the resistance of each fuel injector with one of the following methods:

    • If the engine coolant temperature (ECT) sensor is between 10-32°C (50-90°F), the resistance of each fuel injector should be 11-14 ohms.
       ⇒If the injectors measure OK, perform the Fuel Injector Balance Test -- Fuel Pressure Test.
       ⇒If not within the specified range, replace the fuel injector.
    • If the ECT sensor is not between 10-32°C (50-90°F), measure and record the resistance of each fuel injector with a DMM. Subtract the lowest resistance value from the highest resistance value. The difference between the lowest value and the highest value should be equal to or less than 3 ohms.
       ⇒If the difference is equal to or less than 3 ohms, refer to Fuel Pressure Test for further diagnosis of the fuel injectors.
       ⇒If the difference is more than 3 ohms, add all of the fuel injector resistance values to obtain a total resistance value. Divide the total resistance value by the number of fuel injectors to obtain an average resistance value. Subtract the lowest individual fuel injector resistance value from the average resistance value. Compute the difference between the highest individual fuel injector resistance value and the average resistance value. Replace the fuel injector that displays the greatest difference above or below the average.

Fuel Pressure Test

    Important: 

       • DO NOT perform the Fuel Pressure Test if the engine coolant temperature (ECT) is above 94°C (201°F). Irregular fuel pressure readings may result due to hot soak fuel boiling.
       • Verify that adequate fuel is in the fuel tank before proceeding with this diagnostic.
       • Before proceeding with this test review the User Manual CH 48027-5 for Safety Information and Instructions.

  1. Install a fuel pressure gage. Refer to Fuel Pressure Gage Installation and Removal.
  2. Turn ON the ignition, with the engine OFF.

    3. Important: 

       • The fuel pump relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.
       • DO NOT start the engine.

  3. Command the fuel pump relay ON with a scan tool.
  4. Observe the fuel pressure gage with the fuel pump relay commanded ON. The fuel pressure should be 345-414 kPa (50-60 psi).
    5. ⇒If the fuel pressure is not 345-414 kPa (50-60 psi), refer to Fuel System Diagnosis.
  5. Monitor the fuel pressure gage for five minutes. The fuel pressure should not decrease more than 34 kPa (5 psi).
    6. ⇒If the fuel pressure decreases more than 34 kPa (5 psi), refer to Fuel System Diagnosis.
  6. Perform the Fuel Injector Balance Test.

Fuel Injector Balance Test

  1. Set the selector switch on the fuel injector tester to the Balance Test 50 pulses/10 ms position.
  2. Connect the SA9182E to a fuel injector.
  3. Command the fuel pump relay ON and then OFF three times with a scan tool. On the last command, as the fuel pressure begins to slowly degrade and stabilize, select a fuel pressure within 34 kPa (5 psi) of the maximum pump pressure. Record this fuel pressure. This is the starting pressure at which you will pulse each injector.
  4. Command the fuel pump relay ON one more time and energize the fuel injector by depressing the Activate Injector button on the SA9182E at the previously selected pressure.
  5. After the injector stops pulsing, select Min from the Display Mode and record the Min pressure.

    6. Important: New test results will not be recorded if the Min/Max results are not cleared after each injector is tested.

  6. Clear the Min/Max results.
  7. Select Normal from the Display Mode.
  8. Repeat steps 2 and 4 through 7 for each fuel injector.
  9. Perform the Pressure Drop Calculation.

Pressure Drop Calculation

  1. Subtract the minimum pressure from the starting pressure for one fuel injector. The result is the pressure drop value.
  2. Obtain a pressure drop value for each fuel injector.
  3. Add all of the individual pressure drop values except for the injector suspected of being faulty. This is the total pressure drop.
  4. Divide the total pressure drop by the number of fuel injectors that were added together. This is the average pressure drop. The difference between any individual pressure drop and the average pressure drop should not be more than 20 kPa (3 psi).
    5. ⇒If the difference between any individual pressure drop and the average pressure drop is more than 20 kPa (3 psi), replace the fuel injector(s).

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Fuel Injector Replacement