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Fuel Delivery

NOTE: For connector identification, see CONNECTOR IDENTIFICATION  . For component location, see COMPONENT LOCATIONS  . For circuit identification and wiring diagram, see WIRING DIAGRAMS article. After each repair procedure has been completed, reconnect all components.
  1. Turn ignition on. With DRBIII(R), actuate the ASD Fuel System test. Listen for fuel pump operation at fuel tank. It may be necessary to use a mechanics stethoscope. Does the Fuel Pump operate? If yes, go to next step. If no, go to step  6 .
    2. WARNING: The fuel system is under a constant pressure even with the engine off. Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released.
  2. Turn the ignition off. Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE  . Install a fuel pressure gauge to the fuel rail test port. Turn ignition on. With the DRBIII(R), actuate the ASD Fuel System test and observe the fuel pressure gauge. Fuel pressure specification should be 44.2-54.2 psi (3.1-3.7 kg/cm2 ). Choose a conclusion that best matches your fuel pressure reading. If fuel pressure is below specification, stop all actuations and go to next step. If fuel pressure is within specification, stop all actuations and go to step  5 . If fuel pressure is above specification, stop all actuations. On Grand Cherokee and Wrangler, fuel filter/fuel pressure regulator is defective. Release fuel pressure and replace the fuel filter/fuel pressure regulator. See FUEL FILTER/FUEL PRESSURE REGULATOR under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION article. On Liberty, fuel pressure regulator is defective. Release fuel pressure and replace lower section of fuel pump module. See FUEL PUMP MODULE under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION article. On all models, perform POWERTRAIN VERIFICATION TEST VER-1  under VERIFICATION TESTS.
  3. Release fuel pressure. Raise and support vehicle. Disconnect fuel pressure line from fuel pump module at fuel tank. Connect Fuel Line Pressure Test Adapter Hose (6539) between disconnected fuel line and fuel pump module. Connect fuel pressure gauge to fuel line adapter hose. Turn ignition on. With DRBIII(R), actuate the ASD fuel system test and note fuel pressure. Fuel pressure should be 44.2-54.2 psi (3.23-3.96 kg/cm2 ). If fuel pressure is as specified, stop all actuations. Release fuel pressure, and repair or replace fuel supply line. Perform POWERTRAIN VERIFICATION TEST VER-1  under VERIFICATION TESTS. If fuel pressure is not as specified, stop all actuations and go to next step.
  4. Release fuel pressure. Remove fuel pump module and inspect fuel inlet strainer. See FUEL PUMP MODULE under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION article. If fuel inlet strainer is plugged, replace fuel pump inlet strainer. Perform POWERTRAIN VERIFICATION TEST VER-1  under VERIFICATION TESTS. If fuel inlet strainer in not plugged, replace fuel pump. Perform POWERTRAIN VERIFICATION TEST VER-1  under VERIFICATION TESTS.
  5. Turn ignition off. Release fuel pressure. Disconnect fuel supply line from fuel rail. Install Fuel Line Pressure Test Adapter Hose (6539 for 5/16" fuel lines or 6631 for 3/8" fuel lines) between disconnected fuel line and fuel rail. See Fig 1 . Remove fuel fill cap. Insert other end of hose into a graduated container suitable for gasoline. With DRBIII(R), actuate ASD fuel system test for 7 seconds. Do not operate fuel pump longer than 7 seconds. If fuel volume is .5 pt. (.25L) or more, no problem is indicated at this time. Test is complete. If fuel volume is less than .5 pt. (.25L), check for a kinked fuel line between fuel pump module and fuel rail. Repair fuel lines as necessary and retest. If fuel line is okay, replace fuel pump module assembly. See FUEL PUMP MODULE under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION article. Perform POWERTRAIN VERIFICATION TEST VER-1  under VERIFICATION TESTS.
  6. Turn ignition off. Disconnect fuel pump module connector. Turn ignition on. With DRBIII(R), actuate ASD fuel system test. Using a 12-volt test light connected to ground, probe the Fuel Pump Relay Output circuit at the Fuel Pump Module harness connector. Does the test light illuminate brightly? If yes, go to next step. If no, go to step  9 .
  7. Turn ignition off. Disconnect test light. Using a test light connected to 12-volts, backprobe the Fuel Pump ground circuit at the Fuel Pump Module harness connector. Does the test light illuminate brightly? If yes, go to next step. If no, repair the fuel pump ground circuit for an open or high resistance. Perform POWERTRAIN VERIFICATION TEST VER-1  under VERIFICATION TESTS.
  8. There are no possible causes remaining, replace fuel pump module. Perform POWERTRAIN VERIFICATION TEST VER-1  under VERIFICATION TESTS.
  9. Turn the ignition off. Remove the Fuel Pump Relay from the PDC. Using a 12-volt test light connected to ground, backprobe the Fuel Pump Relay Fused B+ circuit at the PDC. Does the test light illuminate? If yes, go to next step. If no, repair the Fuel Pump Relay Fused B+ circuit for an open. Check for open fuse in the PDC. Perform POWERTRAIN VERIFICATION TEST VER-1  under VERIFICATION TESTS.
  10. Measure the resistance of the Fuel Pump Relay Output circuit from the relay connector to the fuel pump module connector. Is the resistance below 5.0 ohms? If yes, replace the Fuel Pump Relay. Perform POWERTRAIN VERIFICATION TEST VER-1  under VERIFICATION TESTS. If no, repair the Fuel Pump Relay Output circuit for an open. Perform POWERTRAIN VERIFICATION TEST VER-1  under VERIFICATION TESTS.
Fig 1: Identifying Fuel Line Pressure Test Adapter
G00079722Courtesy of DAIMLERCHRYSLER CORPORATION
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