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

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

Number(s) below refer to the step number(s) 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. Tests the ability to maintain a steady fuel pressure 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 perform the A 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 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

With a scan tool, 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 less than 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. Relieve the fuel pressure. Refer to Fuel Pressure Relief .
  2. Reconnect the negative battery cable.
  3. Turn OFF the air conditioning.
  4. With a scan tool, command the fuel pump on.
  5. Wait for the fuel pressure to build.
  6. With the J 34730-1A fuel pressure gauge, observe the fuel pressure.

Does the fuel pressure measure within the specified value?

358-405 kPa (52-59 psi)

Go to Step 6

Go to Fuel System Diagnosis

6

  • With a scan tool, command 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 and J 39021-380 adaptor to a fuel injector.
  2. With the Fuel Injector Tester, select the 0.5-2.5 AMP position.
  3. With a scan tool, command the fuel pump ON 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 fuel injector tester, press the Push to Start Test button.
  6. When the fuel pressure gauge needle stops moving, record the fuel pressure. This is the 2nd pressure reading.
  7. Repeat steps 1 through 6 for each remaining fuel injector.
  8. Subtract the 2nd pressure reading from the 1st pressure reading for each fuel injector. The result is the pressure drop value.
  9. Record 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 or lower than the average pressure drop by the specified value?

10 kPa (1.5 psi)

Go to Step 9

Go to Symptoms

9

Did you complete the procedure?

--

Go to Step 10

--

10

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Symptoms