GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Saturn 🢒 2005 🢒 RELAY 🢒 Body 🢒 Wiring Systems 🢒 Fuel Injector Balance Test with Tech 2
Table 1: Fuel Injector Balance Test Example (Actual Results May Vary)

Circuit Description

The scan tool first energizes the fuel pump and then the fuel injectors for a precise amount of time allowing a measured amount of fuel into the manifold. This causes a drop in system fuel pressure that can be recorded and used to compare each injector.

Fuel Injector Balance Test Example (Actual Results May Vary)

Cylinder

1

2

3

4

1st Reading

379 kPa (55 psi)

379 kPa (55 psi)

379 kPa (55 psi)

379 kPa (55 psi)

2nd Reading

280 kPa (41 psi)

310 kPa (45 psi)

340 kPa (49 psi)

317 kPa (46 psi)

Amount of Drop

99 kPa (14 psi)

69 kPa (10 psi)

39 kPa (6 psi)

62 kPa (9 psi)

Average Range: 47-87 kPa (6.8-12.6 psi)

Replace fuel injector - too much fuel pressure drop

Injector OK

Replace fuel injector - too little fuel pressure drop

Injector OK

Test Description

The number below refers to the step number on the diagnostic table.

  1. The engine coolant temperature (ECT) must be below the operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Did you perform the Fuel Injector Coil Test?

--

Go to Step 3

Go to Fuel Injector Solenoid Coil Test

3

Important : Do not perform this test if the engine coolant temperature (ECT) is above 94°C (201°F).

Observe the ECT parameter with a scan tool.

Is the ECT parameter less that the specified value?

94°C (201°F)

Go to Step 4

--

4

Important: Verify adequate fuel in the fuel tank before proceeding with this diagnostic.

  1. Turn OFF the ignition.
  2. Turn OFF all the accessories.
  3. Install the J 34730-1A Fuel Pressure Gage and the fuel pressure gage fitting. Refer to Fuel Pressure Gage Installation and Removal .
  4. Turn ON the ignition, with the engine OFF.
  5. Command the fuel pump ON with a scan tool.

    6. Important: 

       • You may need to command the fuel pump relay ON a few times in order to obtain the highest possible fuel pressure.
       • Do not start the engine.

  6. Observe the J 34730-1A , with the fuel pump commanded ON.

Is the fuel pressure within the specified value?

384-425 kPa (56-62 psi)

Go to Step 5

Go to Fuel System Diagnosis

5

Important: The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant.

Monitor the J 34730-1A for 1 minute.

Does the fuel pressure decrease by more than the specified value?

34 kPa (5 psi)

Go to Fuel System Diagnosis

Go to Step 6

6
  1. With a scan tool, select the Fuel Injector Balance Test function, within the Special Functions menu.
  2. Select a fuel injector to be tested.
  3. Press Enter in order to prime the fuel system.
  4. Record the fuel pressure indicated by the J 34730-1A after the fuel pressure stabilizes. This is the 1st pressure reading.

    5. Important: Record the fuel pressure value immediately after the fuel injector stops pulsing. The fuel pressure may rise after the fuel injector stops pulsing. Do not record the higher fuel pressure value.

  5. Energize the fuel injector by depressing the Pulse Injector button on the scan tool. This energizes the fuel injector and decreases the fuel pressure.
  6. Record the fuel pressure indicated by the J 34730-1A after the fuel injector has stopped pulsing. This is the 2nd pressure reading.
  7. Press Enter again to bring you back to the Select Injector screen.
  8. Repeat for each fuel injector.
  9. Subtract the 2nd pressure reading from the 1st pressure reading for one fuel injector. The result is the pressure drop value.
  10. Obtain a pressure drop value for each fuel injector.
  11. Add all of the individual pressure drop values. This is the total pressure drop.
  12. Divide the total pressure drop by the number of fuel injectors. This is the average pressure drop.

Does any fuel injector have a pressure drop value that is either higher than the average pressure drop or lower than the average pressure drop by more than the specified value?

20 kPa (3 psi)

Go to Step 7

Go to Symptoms - Engine Controls

7

Replace the affected fuel injector. Refer to Fuel Injector Replacement .

Did you complete the replacement?

--

Go to Step 8

--

8

Operate the vehicle in order to verify the repair.

Does a driveability condition still exist?

--

Go to Symptoms - Engine Controls

System OK