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

Caution: Wrap a shop towel around the fuel pressure connection in order to reduce the risk of fire and personal injury. The towel will absorb any fuel leakage that occurs during the connection of the fuel pressure gage. Place the towel in an approved container when the connection of the fuel pressure gage is complete.

1. The engine coolant temperature 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. If the fuel pressure is not within the specified range, go to Fuel System Pressure Test.

3. The fuel pressure should reach a steady value. If the fuel pressure does not reach a steady value, go to Fuel System Pressure Test.

4. If the pressure drop value for each fuel injector is within 10 kPa (1.5 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.

#### Fuel Injector Balance Test Procedure

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Did you perform the Fuel Injection Coil Test? | -- | Go to Step 3 | Go to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Outside 10-35 Degrees C (50-95 Degrees F)
3 | Important : Do not perform this test if the engine coolant temperature is above 94°C (201°F). Install 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 | Caution: Wrap a shop towel around the fuel pressure connection in order to reduce the risk of fire and personal injury. The towel will absorb any fuel leakage that occurs during the connection of the fuel pressure gage. Place the towel in an approved container when the connection of the fuel pressure gage is complete.

1. Turn OFF the ignition.
2. Connect the J 34730-1A fuel pressure gauge to the fuel pressure test port.
3. Turn ON the ignition, with the engine OFF.
4. With a scan tool, command the fuel pump ON.
5. Place the bleed hose of the fuel pressure gauge into an approved gasoline container.
6. Bleed the air out of the fuel pressure gauge.

Important: The fuel pump will run for approximately 2 seconds. Repeat Step 7 as necessary in order to achieve the highest possible fuel pressure.

7. Command the fuel pump ON.
8. Observe the reading on the fuel pressure gauge while the fuel pump is running.

Does the fuel pressure measure within the specified value?

358-405 kPa (52-59 psi)

Go to Step 5

Go to Fuel System Pressure Test

5 | After the fuel pump stops, the fuel pressure may vary slightly, then should hold steady. Does the fuel pressure remain constant within the specified value? | 358-405 kPa (52-59 psi) | Go to Step 6 | Go to Fuel System Pressure Test
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 pump.
4. Record the fuel pressure indicated by the fuel pressure gauge after the fuel pressure stabilizes. This is the 1st pressure reading.
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 gauge after the fuel pressure gauge needle has stopped moving. 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?

10 kPa (1.5 psi)

Go to Step 7

Go to Symptoms

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