For 1990-2009 cars

### Circuit Description

The scan tool first energizes the fuel pump and then the 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.

### Test Description

The numbers below refer to the step numbers 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.

2. The fuel pressure should be within the specified range. Refer to Fuel System Diagnosis if the fuel pressure is not within the specified range.

3. The fuel pressure should reach a steady value. Refer to Fuel System Diagnosis if the fuel pressure does not stabilize.

4. If the pressure drop value for each fuel injector is within 20 kPa (3 psi) of the average pressure drop value, the fuel injectors are flowing properly. Calculate the pressure drop value for each fuel injector by subtracting the second pressure reading from the first pressure reading.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
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 ECT is above 94°C (201°F). Observe the ECT parameter with a scan tool. Does the scan tool indicate that the ECT parameter is less than the specified value? | 94°C (201°F) | Go to Step 4 | --
4 |

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

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

Important:

• | The fuel pump may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.

• | DO NOT start the engine.

5. Command the fuel pump ON with a scan tool.
6. Observe the fuel pressure gage, with the fuel pump commanded ON.

Is the fuel pressure within the specified range?

345-414 kPa (50-60 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 fuel pressure gage 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 an injector to be tested.
3. Press Enter. This will prime the fuel system.
4. Record the fuel pressure indicated by the fuel pressure gage after the fuel pressure stabilizes. This is the 1st pressure reading.

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 will energize the injector and decrease the fuel pressure.
6. Record the fuel pressure indicated by the fuel pressure gage 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 the specified value?

20 kPa (3 psi)

Go to Step 7

Go to Symptoms - Engine Controls

7 | Perform the Fuel Injector Cleaning . Did you complete the procedure? | -- | Go to Step 8 | --
8 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Symptoms - Engine Controls