GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2000 🢒 Century 🢒 Engine 🢒 Engine Controls - 3.1L (LG8) 🢒 Fuel Injector Balance Test
Table 1: Injector Balance Test Example
Table 2: Fuel Injection Balance Test Procedure

Injector Balance Test Example

Cylinder

1

2

3

4

5

6

1st Reading

380 kPa (55 psi)

380 kPa (55 psi)

380 kPa (55 psi)

380 kPa (55 psi)

380 kPa (55 psi)

380 kPa (55 psi)

2nd Reading

186 kPa (27 psi)

170 kPa (25.5 psi)

186 kPa (27 psi)

235 kPa (34 psi)

180 kPa (24 psi)

201 kPa (29 psi)

Amount of Drop

194 kPa (28 psi)

210 kPa (29.5 psi)

194 kPa (28 psi)

145 kPa (21 psi)

200 kPa (29 psi)

179 kPa (26 psi)

Average Range: 179-200 kPa (26-29 psi)

Injector OK

Faulty injector - too much fuel drop

Injector OK

Faulty injector - too little fuel drop

Injector OK

Injector OK

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  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. Tests the ability to achieve a specified fuel pressure range .

    3.

  3. Tests the ability to maintain a steady fuel pressure value.

    4.

  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. Refer to the Injector Balance Test Example.

Fuel Injection Balance Test Procedure

Step

Action

Values

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 engine coolant temperature is above 94°C (201°F)

With a scan tool, monitor the ECT parameter.

Is the ECT parameter 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 a approved gasoline container.
  6. Bleed the air out of the fuel pressure gauge.

    7. 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 again.
  8. Observe the reading on the fuel pressure gauge.

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. Install the J 39021 fuel injector tester, J 39021 - 210 injector selector switch box and the J 39021-410 fuel injection coil test harness.
  2. Select the 0.5-2.5 AMP position on the fuel injector tester.
  3. With a scan tool, command the fuel pump on and then off.
  4. After the fuel pressure stabilizes, record the fuel pressure on the J 34730-1A fuel pressure gauge. This is the 1st pressure reading.
  5. With the J 39021 - 210 injector selector switch box, select an injector .
  6. Press the Push to Start Test button on the fuel injector tester.
  7. When the fuel pressure gauge needle stops moving, record the fuel pressure. This is the 2nd pressure reading.
  8. Repeat for each remaining fuel injector.
  9. Subtract the 2nd pressure reading from the 1st pressure reading for each fuel injector. The result is the pressure drop value.
  10. Record 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