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Home >> GMC >> 1998 >> C3500 HD 7.4 J, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System & Component Testing 7.4L >> Fuel System >> Fuel Control >> Injector Balance Test
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Injector Balance Test

  1. If powertrain OBD system check has been performed, go to next step. If powertrain OBD system check has not been performed, perform powertrain OBD system check. See POWERTRAIN OBD SYSTEM CHECK in TESTS W/CODES - 7.4L article.
  2. If injector coil test has been performed, go to next step. If injector coil test has not been performed, perform injector coil test. See INJECTOR COIL TEST.
  3. If engine coolant temperature is greater than 201°F (94°C), go to next step. If engine coolant temperature is not greater than 201°F (94°C), go to step 5).
  4. Allow engine to cool to less than 201°F (94°C) and go to next step.
  5. Install fuel pressure gauge. Turn ignition switch to RUN position then to LOCK position. Bleed air from fuel pressure gauge. Using scan tool, energize fuel pump. If fuel pressure reading is 60-66 psi (4.2-4.6 kg/cm2 ), go to next step. If fuel pressure reading is not within specification, perform fuel system diagnosis. See BASIC TESTING - 7.4L article.
  6. Turn fuel pump off. Observe fuel pressure gauge. If fuel pressure remains constant, go to next step. If fuel system does not remain constant, perform fuel system diagnosis. See BASIC TESTING - 7.4L article.
    NOTE: Perform step 7) on each injector.
  7. Disconnect fuel injectors harness connector. Using Fuel Injector Adapter (J-34730-3A), connect Fuel Injector Tester (9J-39021) to fuel injector. Connect fuel injector tester power leads to appropriate battery terminals. Set amperage supply selector switch on fuel injector tester to Balance Test 0.5-2.5 amp position. Turn ignition switch to RUN position then to LOCK position. Record fuel pressure reading (first reading). Energize injector by depressing PUSH TO START TEST button on injector tester and hold until fuel pressure gauge stabilizes. Record fuel pressure reading (second reading). Subtract first reading from second reading (this result is pressure drop valve). Add pressure drop valve for each injector together and divide total by 4. If any injector's drop valve is greater or less than average drop valve by 1.5 psi (.1 kg/cm2 ), replace faulty injector(s) as necessary. If no injector's drop valve is greater or less than average drop valve by 1.5 psi (.1 kg/cm2 ), injector balance test is okay at this time.
WARNING: In order to prevent flooding of cylinder and possible engine damage, relieve fuel pressure before performing injector coil test procedure.
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