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Diagnostic Aids

Engine coolant temperatures greater than normal operating temperature may cause irregular fuel pressure because of HOT SOAK fuel boiling. If fuel pressure is not within specification, go to TEST A1-7B  under CIRCUIT TESTS. If fuel pressure does not reach a stable fuel pressure, go to TEST A1-7B  under CIRCUIT TESTS.

If fuel pressure drop for each fuel injector is within 1.5 psi (0.11 kg/cm2 ) of average fuel pressure drop for all injectors, fuel injector is operating properly. Fuel pressure drop is the difference between the first fuel pressure reading and the second fuel pressure reading. If fuel injector pressure drop is greater than average fuel pressure drop specification, fuel injector is to rich. If fuel injector pressure drop is less than average fuel pressure drop specification, fuel injector is lean. Replace fuel injector if fuel injector pressure drop is not within specification.

  1. Connect scan tool to DLC. Observe coolant temperature. If coolant temperature is greater than 201°F (94°C), allow engine to cool below specified temperature and go to next step.
  2. Relieve fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE  under FUEL SYSTEM. Install fuel pressure gauge. Place bleed hose of fuel pressure gauge into approved container. Connect a fused jumper wire between underhood DLC terminals Fp and +B. Fuel pump should run. Bleed air from gauge and observe gauge reading. If fuel pressure is 38-44 psi (2.7-3.1 kg/cm2 ), go to next step. If fuel pressure is not as specified, go to TEST A1-7B  under CIRCUIT TESTS.
  3. Remove fused jumper wire. Observe fuel pressure gauge. If fuel pressure stays constant, go to next step. If fuel pressure does not remain constant, go to TEST A1-7B  under CIRCUIT TESTS.
  4. Connect Fuel Injector Adapter (J-34730-3A) and Fuel Injector Tester (J-39021) to a fuel injector following manufacturer's instructions. Set amperage switch on tester to BALANCE TEST 0.5-2.5 AMP position. Using a fused jumper wire, momentarily connect underhood DLC terminals Fp and +B to pressurize fuel system. Record fuel pressure after reading stabilizes and label as the first pressure reading. Depress PUSH TO START TEST button on tester to energize fuel injector. Record fuel pressure after reading stabilizes and label as the second pressure reading. Record first and second pressure reading for remaining injectors.
  5. Subtract second pressure reading from first reading to obtain a pressure drop value. Repeat for remaining injectors. Add all pressure drop values and divide by number of injectors to obtain average pressure drop value. If any injector has a pressure drop of 1.5 psi (.11 kg/cm2 ) greater or less than average pressure drop value, go to next step. If fuel injector pressure drop is within 1.5 psi (.11 kg/cm2 ) of average pressure drop, fuel injector is operating properly. See the TESTS W/O CODES article.
    CAUTION: To prevent engine flooding, do not repeat any portion of this test before starting and running engine.
  6. Retest any fuel injector that does not meet specified fuel pressure drop. Replace faulty injectors as necessary. Go to ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in the TESTS W/CODES article. If fuel injector(s) is okay, see the TESTS W/O CODES article.
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