GM Service Manual Online
For 1990-2009 cars only
Table 1: Injector Balance Test Example
Table 2: Test Procedure

Object Number: 17713  Size: SF
(1)First Reading
(2)Second Reading

Injector Balance Test Example

Cylinder

1

2

3

4

5

6

1st Reading

296 kPa (43 psi)

296 kPa (43 psi)

296 kPa (43 psi)

296 kPa (43 psi)

296 kPa (43 psi)

296 kPa (43 psi)

2nd Reading

131 kPa (19 psi)

117 kPa (17 psi)

124 kPa (18 psi)

145 kPa (21 psi)

131 kPa (19 psi)

130 kPa (19 psi)

Amount of Drop

165 kPa (24 psi)

179 kPa (26 psi)

172 kPa (25 psi)

151 kPa (22 psi)

165 kPa (24 psi)

166 kPa (24 psi)

Average Range: 156-176 kPa (22.5-25.5 psi)

Injector OK

Faulty injector - too much fuel drop

Injector OK

Faulty injector - too little fuel drop

Injector OK

Injector OK

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.

  3. The fuel pressure should reach a steady value.

  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.

Test Procedure

Step

Action

Value(s)

Yes

No

1

Did you preform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Did you preform the Fuel Injector Coil Test Procedure?

--

Go to Step 3

Go to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Outside 10-35 Degrees C (50-95 Degrees F)

3

Does the engine coolant temperature measure above the specified value?

94°C (201°F)

Go to Step 4

Go to Step 5

4

Allow the engine to cool below the specified value.

Does the engine coolant temperature measure below the specified value?

94°C (201°F)

Go to Step 5

--

5

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. Install the fuel pressure gauge.
  2. Energize the fuel pump using the scan tool.
  3. Place the bleed hose of the fuel pressure gauge into an approved gasoline container.
  4. Bleed the air out of the fuel pressure gauge.
  5. Using a scan tool pressurize the fuel system.
  6. Wait for the fuel pressure to build.
  7. Important: The fuel pump will run for approximately 2 seconds. Repeat Step 5 as necessary in order to achieve the highest possible fuel pressure.

  8. Observe the reading on the fuel pressure gauge.

Does the fuel pressure measure within the specified limits?

284-325 kPa (41-47 psi)

Go to Step 6

Go to Fuel System Diagnosis

6

Turn the fuel pump OFF.

Does the fuel pressure remain constant?

--

Go to Step 7

Go to Fuel System Diagnosis

7

  1. Connect the J 39021 fuel injector tester to a fuel injector.
  2. Set the amperage supply selector switch on the fuel injector tester to the Balance Test 0.5-2.5 amp position.
  3. Turn the fuel pump ON then OFF in order to pressurize the fuel system.
  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 Push to Start Test button on the fuel injector tester.
  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. Repeat Steps 1 through 6 for each fuel injector.
  8. Subtract the 2nd pressure reading from the 1st pressure reading for one fuel injector. The result is the pressure drop value.
  9. Obtain a pressure drop value for each fuel injector.
  10. Add all of the individual pressure drop values. This is the total pressure drop.
  11. 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 8

Go to Symptoms

8

Notice: Do Not repeat any portion of this test before running the engine in order to prevent the engine from flooding.

Re-test any fuel injector that does not meet the specification. Refer to the procedure in Step 7.

Does any fuel injector still 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 9

Go to Symptoms

9

Replace the faulty fuel injector(s). Refer to Fuel Injector Replacement

Did you complete the Replacment?

--

System OK

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