Engine Controls - Basic Testing: Diagnosis Jeep Cherokee II рестайлинг

VISUAL INSPECTION

Most driveability problems in the engine control system result from faulty wiring, poor electrical connections or leaking air and vacuum hose connections. To avoid unnecessary component testing, perform a visual inspection before beginning self-diagnostic tests.

Visually inspect all electrical wiring, looking for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and are not cracked, pinched or cut. See VACUUM DIAGRAMS article. Inspect air induction system for possible vacuum leaks.

MECHANICAL INSPECTION

Check engine mechanical condition with a compression gauge, vacuum gauge or scan tool. See scan tool manual for specific instructions.

FUEL PRESSURE TEST

Note. For additional information on fuel pressure and fuel pump testing procedures, see CHRYSLER CORP. - SELF-DIAGNOSTICS - JEEP, TRUCKS & RWD VANS article.

Note. All models are equipped with a mechanical fuel pressure regulator located in fuel tank, inside fuel pump module. Excess fuel is returned to tank through fuel pressure regulator.

1. Release fuel pressure. See «FUEL PRESSURE RELEASE»(ref-614-S29217357452000030800000) . Remove test port cap. Install a 0-60 psi (0-4.2 kg/cm 2 ) fuel pressure gauge at test port.
2. Start engine and allow to idle. Fuel pressure should be 44.2-54.2 psi (3.1-3.7 kg/cm 2 ). If no fuel pressure exists, fuel pump relay control circuit may be defective. See CHRYSLER CORP. - SELF-DIAGNOSTICS - JEEP, TRUCKS & RWD VANS article.
3. If fuel pressure exceeds specification, fuel pump is okay, but fuel pressure regulator is defective. Release fuel pressure and replace fuel pump module. See REMOVAL, OVERHAUL & INSTALLATION article.
4. If fuel pressure is okay, release fuel pressure. Remove test gauge hose. Install test port cap.

FUEL SYSTEM PRESSURE LEAK-DOWN TEST

1. Release fuel pressure. See «FUEL PRESSURE RELEASE»(ref-614-S29217357452000030800000) . Ensure area around fuel supply line and fuel rail are clean. Disconnect fuel supply line from fuel rail.
2. Install Fuel Line Pressure Test Adapter Tool Hose (6539 for 5/16" fuel lines; 6631 for 3/8" fuel lines) between disconnected fuel line and fuel rail. Connect 0-60 psi (0-4.2 kg/cm 2 ) fuel pressure test gauge from Gauge Set (5069) to test port on adapter tool.
3. Ensure no fuel leaks exist and start engine. Warm engine to normal operating temperature. Fuel pressure should be 44.2-54.2 psi (3.1-3.7 kg/cm 2 ). Shut engine off. Pressure should not fall below 30 psi (2.1 kg/cm 2 ) for 5 minutes.
4. If pressure falls below 30 psi (2.1 kg/cm 2 ), start engine and warm to normal operating temperature. Shut engine off. Clamp rubber hose between fuel rail and test port on adapter tool. If pressure still does not hold, repair leaking fuel injector or fuel rail. If pressure holds at 30 psi (2.1 kg/cm 2 ) or more, go to next step.
5. Remove clamp from hose. Start engine and allow to reach operating temperature. Shut engine off. Clamp hose between fuel supply line and adapter test port. If pressure does not drop to less than 30 psi (2.1 kg/cm 2 ) for 5 minutes, check and repair leaking fuel lines or connections. If lines and connections are okay, replace fuel pump module.

FUEL PUMP VOLUME TEST

1. Perform «FUEL PRESSURE TEST»(ref-614-S27857093602000030800000) . If fuel pressure is okay, relieve fuel system pressure. See «FUEL PRESSURE RELEASE»(ref-614-S29217357452000030800000) . Ensure area around fuel supply line and fuel rail are clean.
2. Disconnect fuel supply line from fuel rail. Install Fuel Line Pressure Test Adapter Tool Hose (6539 for 5/16" fuel lines; 6631 for 3/8" fuel lines) between disconnected fuel line and fuel rail. Remove fuel fill cap. Insert other end of hose into a graduated container suitable for gasoline.
3. Connect scan tool to data link connector. Using scan tool, actuate fuel pump. If fuel volume is not as specified, but fuel pump can be heard through fuel fill pipe, check for a kinked fuel line. See «FUEL PUMP PERFORMANCE»(ref-614-S17717118342000030800000) table.
4. If fuel line is okay and fuel pressure is okay, but volume is low, replace fuel filter/fuel pressure regulator. Fuel filter/regulator may be serviced separately on some models. If fuel pressure and volume are low, replace fuel pump module assembly.

FUEL PUMP PERFORMANCE (1)

FUEL PUMP RELAY TEST

Note. For fuel pump relay test procedure, see RELAYS under MODULES, MOTORS & RELAYS in SYSTEM & COMPONENT TESTING article.