Home ReviewsRefund
Home/Jeep/Grand Cherokee/Jeep Grand Cherokee ZJ рестайлинг (1996-1998)/Repair manual/Testing & Diagnostics/Engine Controls - Basic Testing - 4.0l
Contents Section: Testing & Diagnostics All sections

Engine Controls - Basic Testing - 4.0l Jeep Grand Cherokee ZJ рестайлинг

Testing & Diagnostics ~1760 words

INTRODUCTION

The following diagnostic steps will help prevent overlooking a simple problem. This is also where to begin diagnosis for a no-start condition.

The first step in diagnosing any driveability problem is verifying the customer's complaint with a test drive under the conditions the problem reportedly occurred.

Before entering self-diagnostics, perform a careful and complete visual inspection. Most engine control problems result from mechanical breakdowns, poor electrical connections or damaged/misrouted vacuum hoses. Before condemning the computerized system, perform each test listed in this article.

Note. Unless stated otherwise in test procedure, perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) having a minimum 10-megohm input impedance.

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 - 4.0L article. Inspect air induction system for possible vacuum leaks.

MECHANICAL INSPECTION

WARNINGDO NOT use ignition switch during compression tests on fuel injected vehicles. Use a remote starter to crank engine. Fuel injectors are triggered by ignition switch during cranking mode, which can create a fire hazard or contaminate the engine's oilingsystem.

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

Compression

Ensure battery is fully charged and starter motor is in good operating condition. Clean spark plug recesses with compressed air and remove spark plugs. Lock throttle in Wide Open Throttle (WOT) position and Remove Auto Shutdown (ASD) relay. Install compression gauge. Using a remote starter switch, rotate engine 3 revolutions. Record compression pressure from third revolution. Continue test for remaining cylinders. See COMPRESSION SPECIFICATIONS table for correct engine compression pressures. A 50-70 percent reduction in compression between adjacent cylinders indicates a head gasket leak.

ApplicationSpecification
Compression Ratio8.7:1
Compression Pressure
Normal120-150 psi (8.3-10.5 kg/cm 2 )
Maximum Variation Between Cylinders30 psi (2.1 kg/cm 2 )

COMPRESSION SPECIFICATIONS

FUEL SYSTEM

WARNINGALWAYS relieve fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components.
CAUTIONWhen battery is disconnected, vehicle computer and memory systems may lose memory data. Driveability problems may exist until computer systems have completed a relearn cycle. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION before disconnecting battery.

Basic diagnosis of fuel system should begin with determining fuel system pressure.

Fuel Rail With Fuel Pressure Test Port

  1. Disconnect negative battery cable. Remove fuel tank cap to release fuel tank pressure.
  2. Remove protective cap from fuel pressure test port on fuel rail. Place one end of Fuel Pressure Gauge (5069) hose into approved gasoline container. Screw remaining end of fuel pressure gauge hose onto fuel pressure test port. Fuel pressure will be released into gasoline container.
  3. After fuel pressure is released, remove fuel pressure gauge hose from fuel pressure test port. Reinstall protective cap on fuel pressure test port and fuel tank cap. Reinstall negative battery cable.

Fuel Rail Without Fuel Pressure Test Port

  1. Remove fuel pump relay from Power Distribution Center (PDC), located near windshield washer reservoir. Refer to label on PDC cover for relay location.
  2. Start engine and allow to idle until engine stalls. Attempt to start engine several times. Once engine will not restart, turn ignition off.
  3. Disconnect electrical connector from any fuel injector. Connect a jumper wire between one fuel injector terminal and positive battery terminal. Connect another jumper wire to remaining fuel injector terminal. CAUTION: DO NOT apply battery voltage to fuel injector for more than 4 seconds, or fuel injector may be damaged.
  4. Momentarily touch remaining end of jumper wire to negative battery terminal for no more than 4 seconds. Cover fuel line at fuel rail with shop towel before disconnecting. Disconnect fuel line.
  5. Disconnect jumper wires. Reinstall electrical connector on fuel injector. Reinstall fuel pump relay. Diagnostic Trouble Codes (DTCs) may be stored in Powertrain Control Module (PCM) when ASD relay is removed. To clear DTCs from PCM, see «TESTS W/CODES - 4.0L»(/jeep/grand-cherokee/zj-1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-40l) article.

FUEL PRESSURE TEST

Note. For additional information on fuel pressure and fuel pump testing, see TEST NTC-3A and appropriate NS TEST in TESTS W/CODES - 4.0L 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. 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 47-51 psi (3.4-3.7 kg/cm 2 ). If no fuel pressure exists, fuel pump control circuit may be defective. See TEST TC-101A in «TESTS W/CODES - 4.0L»(/jeep/grand-cherokee/zj-1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-40l) 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 «REMOVE/INSTALL/OVERHAUL - 4.0L»(/jeep/grand-cherokee/zj-1996-1998/remont/removal-installation/#how-to-overhaul-installation-40l-the-engine-controls-removal) article.
  4. If fuel pressure is okay, release fuel pressure. Remove test gauge hose. Install test port cap.
  1. Release fuel pressure. See «FUEL PRESSURE RELEASE»(/jeep/grand-cherokee/zj-1996-1998/remont/testing-diagnostics/#engine-controls-basic-testing-40l) . Ensure area around fuel supply line and fuel rail are clean. Note direction of latch clip installation. Latch clip is located on top of fuel supply line at fuel rail. Using 2 screwdrivers, pry latch clip upward, and remove from fuel rail.
  2. Pull fuel supply line from fuel rail. Install appropriate adapter into fuel rail. See FUEL RAIL ADAPTER APPLICATION table. Ensure adapter is fully seated in fuel rail. Install adapter latch clip into fuel rail, with latch clip fingers pointing downward. If latch clip will not fully seat so latch clip fingers extend downward below fitting on fuel rail, adapter may not be fully seated in fuel rail. FUEL RAIL ADAPTER APPLICATION Application Adapter No. 4.0L 6541
  3. Connect fuel supply line to adapter. Ensure fuel supply line fully seats in adapter. Remove protective cap from adapter test port, and install a 0-60 psi (0-4.2 kg/cm 2 ) fuel pressure gauge at test port.
  4. Start engine and allow to idle. Fuel pressure should be 47-51 psi (3.4-3.7 kg/cm 2 ). If no fuel pressure exists, fuel pump control circuit may be defective. See TEST TC-101A in «TESTS W/CODES - 4.0L»(/jeep/grand-cherokee/zj-1996-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes-40l) article.
  5. If fuel pressure exceeds specification, fuel pump is okay, but fuel pressure regulator is defective. Release fuel pressure and replace fuel pump module. See «REMOVE/INSTALL/OVERHAUL - 4.0L»(/jeep/grand-cherokee/zj-1996-1998/remont/removal-installation/#how-to-overhaul-installation-40l-the-engine-controls-removal) article.
  6. If fuel pressure is okay, release fuel pressure. Remove latch clip. Remove test equipment. Before reinstalling fuel supply line, ensure fuel supply line fitting and fitting on fuel rail are clean. Lubricate fuel supply line fitting and fitting on fuel rail with engine oil. Install fuel supply line on fuel rail.
  7. Install latch clip into fuel rail, with latch clip fingers pointing downward. Ensure latch clip is fully seated. Latch clip fingers should extend downward below fitting on fuel rail when fully seated.
  8. Pull on fuel supply line to ensure fuel supply line is fully locked on fuel rail. Start engine and check for fuel leaks.

FUEL SYSTEM PRESSURE LEAK DOWN TEST

  1. Release fuel pressure. See «FUEL PRESSURE RELEASE»(/jeep/grand-cherokee/zj-1996-1998/remont/testing-diagnostics/#engine-controls-basic-testing-40l) . Ensure area around fuel supply line and fuel rail are clean. Note direction of latch clip installation. Latch clip is located on top of fuel supply line at fuel rail. Using 2 screwdrivers, pry latch clip upward, and remove from fuel rail.
  2. Pull fuel supply line from fuel rail. Install appropriate adapter into fuel rail. See FUEL RAIL ADAPTER APPLICATION table below. Ensure adapter is fully seated in fuel rail. Install adapter latch clip into fuel rail, with latch clip fingers pointing downward. If latch clip will not fully seat so latch clip fingers extend downward below fitting on fuel rail, adapter may not be fully seated in fuel rail. FUEL RAIL ADAPTER APPLICATION Application Adapter No. 4.0L 6541
  3. Connect fuel supply line to adapter. Ensure fuel supply line fully seats in adapter. Remove protective cap from adapter test port, and install a 0-60 psi (0-4.2 kg/cm 2 ) fuel pressure gauge at test port.
  4. Start engine and allow to reach operating temperature. Shut engine off. Wait 5 minutes and check fuel pressure. Fuel pressure should not drop to less than 24 psi (1.7 kg/cm 2 ). If pressure is not as specified, go to next step.
  5. Start engine and allow to reach operating temperature. Shut engine off. Clamp hose between fuel rail adapter and adapter test port. If pressure does not drop to less than 24 psi (1.7 kg/cm 2 ) for 5 minutes, repair leaking fuel injector(s). If pressure is not as specified, go to next step.
  6. 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 24 psi (1.7 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»(/jeep/grand-cherokee/zj-1996-1998/remont/testing-diagnostics/#engine-controls-basic-testing-40l__fuel-pressure-test) . If fuel pressure is okay, relieve fuel system pressure. See «FUEL PRESSURE RELEASE»(/jeep/grand-cherokee/zj-1996-1998/remont/testing-diagnostics/#engine-controls-basic-testing-40l) . Ensure area around fuel supply line and fuel rail are clean. Note direction of latch clip installation. Latch clip is located on top of fuel supply line at fuel rail. Using 2 screwdrivers, pry latch clip upward, and remove from fuel rail.
  2. Pull fuel supply line from fuel rail. Install appropriate adapter into fuel rail. See FUEL RAIL ADAPTER APPLICATION table. Ensure adapter is fully seated in fuel rail. Install adapter latch clip into fuel rail, with latch clip fingers pointing downward. If latch clip will not fully seat so latch clip fingers extend downward below fitting on fuel rail, adapter may not be fully seated in fuel rail. FUEL RAIL ADAPTER APPLICATION Application Adapter No. 4.0L 6541 CAUTION: DO NOT operate fuel pump longer than 7 seconds.
  3. Connect fuel supply line to adapter. Ensure fuel supply line fully seats in adapter. Insert other end of adapter into a graduated container suitable for gasoline. Connect scan tool to data link connector. Using scan tool, actuate fuel pump. If fuel volume is not as specified, check for a plugged fuel filter, kinked fuel line or fuel pump tank module. See «FUEL PUMP PERFORMANCE»(/jeep/grand-cherokee/zj-1996-1998/remont/testing-diagnostics/#engine-controls-basic-testing-40l) table.
ApplicationPsi (kg/cm 2 )Minimum Volume In 7 sec.
All Models44.2-54.2 (3.1-3.7).5 Pt. (.25L)
(1) DO NOT operate fuel pump longer than 7 seconds.
(1)DO NOT operate fuel pump longer than 7 seconds.

FUEL PUMP PERFORMANCE (1)

FUEL PUMP RELAY TEST

Note. For fuel pump relay test procedure, see RELAYS under MODULES, MOTORS & RELAYS in SYSTEM/COMPONENT TESTS - 4.0L article.

IGNITION CHECKS

Note. For ignition system spark and component testing, see appropriate NO TROUBLE CODE (NTC) TEST and NO START (NS) TEST in TESTS W/CODES - 4.0L article.

SUMMARY

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to TESTS W/CODES - 4.0L article. If no hard codes are found in self-diagnostics, proceed to appropriate TESTS W/O CODES - 4.0L article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.

More articles — Engine Performance