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  • 1. ZJ EMISSION CONTROL SYSTEMS 25 - 1 EMISSION CONTROL SYSTEMS CONTENTS page pageCOMPONENT REMOVAL/INSTALLATION . . . . . . 15 EXHAUST EMISSION CONTROLS . . . . . . . . . . . 11EVAPORATIVE EMISSION CONTROLS . . . . . . . . 5 GENERAL INFORMATION . . . . . . . . . . . . . . . . . . 1 GENERAL INFORMATION INDEX page pageDRB Scan Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Vacuum Hose Routing Schematics . . . . . . . . . . . . . 1On-Board Diagnostics . . . . . . . . . . . . . . . . . . . . . . . 1 Vehicle Emission Control Information (VECI) Label . 1VEHICLE EMISSION CONTROL INFORMATION glish and French languages. These labels are perma-(VECI) LABEL nently attached and cannot be removed without All vehicles are equipped with a combined VECI la- defacing information and destroying label.bel. The label is located in the engine compartment The VECI label illustration (Fig. 2) is used as(Fig. 1). The label contains the following: an example only. Refer to the VECI label located in• Engine family and displacement the engine compartment (Fig. 1) for actual emission• Evaporative family information.• Emission control system schematic• Certification application VACUUM HOSE ROUTING SCHEMATICS• Engine timing specifications (if adjustable) The vacuum hose routing schematics are used• Idle speeds (if adjustable) as examples only. If there are any differences be-• Spark plug and plug gap tween these schematics and the Vehicle Emission Control Information (VECI) label schematics, those shown on the VECI label should be used. ON-BOARD DIAGNOSTICS FOR CERTAIN EMISSION SYSTEM COMPONENTS The powertrain control module (PCM) performs an On-Board Diagnostic (OBD) check for certain emis- sion system components on all vehicles. This is done by setting a diagnostic trouble code (DTC). A DTC can be obtained in two different ways. One of the ways is by connecting the DRB scan tool to the data link connector. This connector is located in the engine compartment (Fig. 3). Refer to the appropriate Powertrain Diagnostic Procedures service manual for operation of the DRB scan tool. The other way is to Fig. 1 VECI Label Location—Typical cycle the ignition key and observe the malfunction in- The label also contains an engine vacuum sche- dicator lamp (MIL). The MIL lamp is displayed onmatic. There are unique labels for vehicles built for the instrument panel as the CHECK ENGINE lampsale in the state of California and the country of (Fig. 4). This lamp will flash a numeric code. If a nu-Canada. Canadian labels are written in both the En- meric code number 32 is observed, a problem has
  • 2. 25 - 2 EMISSION CONTROL SYSTEMS ZJ Fig. 2 VECI Label—Typicalbeen found in the EGR system. If a numeric code initially for approximately two seconds each time thenumber 31 is observed, a problem has been found in ignition key is turned to the ON position. This isthe EVAP system. done for a bulb test. EGR System Check: The OBD check will activate For a complete operational description of allonly during selected engine/driving conditions. When DTC’s, for accessing a DTC and for erasing athe conditions are met, the PCM energizes the EGR DTC, refer to On-Board Diagnostics. This canvalve control solenoid to disable the EGR. The PCM be found in the General Diagnosis sections ofchecks for a change in the oxygen sensor signal. If Group 14, Fuel System. For numeric flash lampthe air-fuel mixture goes lean, the PCM will attempt code charts for emission related components,to enrichen the mixture. The PCM registers a diag- refer to Diagnostic Trouble Code (DTC). Thisnostic trouble code (DTC) if the EGR system has can also be found in the General Diagnosis sec-failed or degraded. After registering a DTC, the PCM tions of Group 14, Fuel System.turns the CHECK ENGINE lamp on. Illumination ofthis lamp indicates the need for immediate service.Note that the CHECK ENGINE lamp will illuminate VACUUM ROUTING SCHEMATIC—NON-CALIFORNIA 4.0L ENGINE—TYPICAL
  • 3. ZJ EMISSION CONTROL SYSTEMS 25 - 3 VACUUM ROUTING SCHEMATIC—CALIFORNIA 4.0L ENGINE—TYPICAL VACUUM ROUTING SCHEMATIC—5.2L V-8 ENGINE—TYPICAL
  • 4. 25 - 4 EMISSION CONTROL SYSTEMS ZJ Fig. 4 Check Engine Lamp Location Fig. 3 Data Link Connector—TypicalDRB SCAN TOOL For operation of the DRB scan tool, refer to the ap-propriate Powertrain Diagnostic Procedures servicemanual.
  • 5. ZJ EMISSION CONTROL SYSTEMS 25 - 5 EVAPORATIVE EMISSION CONTROLS INDEX page pageCrankcase Breather/Filter—5.2L Engines . . . . . . . . 10 Fuel Tank Filler Tube Cap . . . . . . . . . . . . . . . . . . . . 7Crankcase Ventilation System—4.0L 6-Cylinder Positive Crankcase Ventilation System—5.2L V-8 Engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7EVAP (Evaporation) Control System . . . . . . . . . . . . 5 Pressure Relief/Rollover Valve . . . . . . . . . . . . . . . . 10EVAP (EVAPORATION) CONTROL SYSTEMGENERAL INFORMATION The function of the EVAP control system is to pre-vent the emissions of gasoline vapors from the fueltank into the atmosphere. When fuel evaporates inthe fuel tank, the vapors pass through vent hoses ortubes to a carbon filled EVAP canister. They are tem-porarily held in the canister until they can be drawninto the intake manifold when the engine is running. The EVAP canister is a feature on all models forthe storage of fuel vapors from the fuel tank. Refer tothe following EVAP Canister for information. Three different EVAP systems are used. These arefor:• The 4.0L six-cylinder engine without the Califor-nia emission package.• The 4.0L six-cylinder engine with the Californiaemission package. Fig. 1 Canister Location—All Engines—Non-• The 5.2L V-8 engine. California Refer to the following System Operation sectionsfor information. SYSTEM OPERATION The hoses used in this system are speciallymanufactured. If replacement becomes neces- 4.0L ENGINE WITHOUT CALIFORNIA EMISSION PACKAGEsary, it is important to use only fuel resistant This is a non-electrical, vacuum operated system.hose. The EVAP canister is equipped with a vacuum con- trolled purge shutoff switch (orifice) (Fig. 3) that con-EVAP CANISTER trols canister purge operation. The switch is open A sealed, maintenance free, EVAP canister is used when engine manifold vacuum is applied to it. Whenon all vehicles. Depending on engine and emission the engine is operating, the EVAP canister purgepackages, two different types of canisters are used. function draws fresh air through the top of the can-The EVAP canister is located in the left front corner ister. This causes the stored vapors to be drawn outof the vehicle below the left front headlamp (Figs. 1 of the canister and into the airstream in the airor 2). The canister is filled with granules of an acti- cleaner housing snorkel (Fig. 3).vated carbon mixture. Fuel vapors entering the can- The air cleaner contains a venturi in the airister are absorbed by the charcoal granules. cleaner cover used as a purge line vacuum source A separate EVAP canister filter is used on 4.0L (Fig. 4). The venturi effect increases the speed of the6-cylinder engines equipped with the California intake air flowing by the slots in the venturi wall.Emission Package only. This filter is located in the This creates a low pressure area around the slots.left front corner of the engine compartment behind When the purge shutoff switch is open, vapors fromthe air cleaner housing. On the 5.2L V-8 engine, this the canister are drawn through slots and into the air-filter is located at the end of the vacuum line harness stream flowing through the venturi (Fig. 4).where the connection is made at the EVAP purge so- The fuel vapors then pass through the intake man-lenoid. On the 4.0L engine without the California ifold and into the engine combustion chambers. Herepackage, the engine air cleaner housing is used. they are consumed during engine combustion.
  • 6. 25 - 6 EMISSION CONTROL SYSTEMS ZJ Fig. 4 Air Cleaner Venturi—Non-California 4.0L Fig. 2 Canister Location—California Emission Engine—Typical Package—4.0L Only trol module (PCM) operates the purge solenoid by controlling the ground circuit to it.Fig. 3 EVAP System—Non-California 4.0L Engine— Typical Fig. 5 Purge Solenoid—4.0L Engine—CaliforniaSYSTEM OPERATION Emission Package4.0L ENGINE WITH CALIFORNIA EMISSION PACKAGE During the cold start warm-up period and the hot This is a combination electrical and vacuum oper- start time delay, the PCM does not energize the sole-ated system. noid. When de-energized (pulse ground signal not The duty cycle EVAP canister purge solenoid (Fig. supplied), no vapors are purged.5) regulates the rate of vapor flow from the EVAP The engine enters closed loop operation after itcanister to the intake manifold. The powertrain con- reaches a specified temperature and the programmed time delay ends. During closed loop operation, the
  • 7. ZJ EMISSION CONTROL SYSTEMS 25 - 7PCM energizes and de-energizes the solenoid 5 to 10 into the engine combustion chambers. Here they aretimes per second, depending upon operating condi- consumed during engine combustion.tions. The PCM varies the vapor flow rate by chang- The EVAP canister purge solenoid will also be en-ing the solenoid pulse width. Pulse width is the ergized during certain idle conditions in order to up-amount of time the solenoid is energized. date the fuel delivery calibration. As the solenoid is energized, the fuel vapors thenpass through the intake manifold and into the engine FUEL TANK FILLER TUBE CAPcombustion chambers. Here they are consumed dur- The fuel tank filler tube cap (fuel tank cap) incor-ing engine combustion. porates a two-way relief valve that is closed to atmo- sphere during normal operating conditions. The reliefSYSTEM OPERATION valve used in fuel filler caps of all models is cali- brated at a pressure of 10 kPa (1.5 psi) or a vacuum5.2L V-8 ENGINE of 6 kPa (1.8 in. Hg). When the pressure or vacuum This is a combination electrical and vacuum oper- is relieved, the valve returns to the normally closedated system. position. Fuel tank pressure vents into the EVAP canister. CAUTION: The fuel filler cap must be removed priorFuel vapors are temporarily held in the canister until to disconnecting any fuel system component.they can be drawn into the intake manifold. TheEVAP canister purge solenoid allows the EVAP can-ister to be purged at predetermined times and at cer- CRANKCASE VENTILATION SYSTEM—4.0Ltain engine operating conditions. 6-CYLINDER ENGINE Vacuum for the EVAP canister is controlled by the The 4.0L engine is equipped with a Crankcase Ven-EVAP canister purge solenoid (Fig. 6). The solenoid is tilation (CCV) system (Fig. 7). The CCV system per-operated by the powertrain control module (PCM). forms the same function as a conventional PCVThe PCM regulates the solenoid by switching the system, but does not use a vacuum controlled valve.ground circuit on and off based on engine operating A molded vacuum tube connects manifold vacuumconditions. When energized (grounded), the solenoid to top of cylinder head cover at dash panel end. Theprevents vacuum from reaching the EVAP canister. vacuum tube contains a fixed orifice (Fig. 7) of a cal-When not energized, the solenoid allows vacuum to ibrated size. It meters the amount of crankcase va-flow through to the EVAP canister. pors drawn out of the engine. A fresh air supply hose from the air cleaner (Fig. 7) is connected to front of cylinder head (valve) cover. When the engine is operating, fresh air enters the engine and mixes with crankcase vapors. Manifold vacuum draws the vapor/air mixture through the fixed orifice and into the intake manifold. The vapors are then consumed during engine combustion. POSITIVE CRANKCASE VENTILATION SYSTEM— 5.2L V-8 ENGINE DESCRIPTION/OPERATION The 5.2L V-8 engine is equipped with a closed pos- itive crankcase ventilation (PCV) system (Fig. 8). This system consists of a crankcase PCV valve mounted on the cylinder head cover with a hose ex- tending from the valve to the intake manifold. Fig. 6 Purge Solenoid—5.2L Engine—Typical A closed engine crankcase breather/filter, with a During warm-up and for a specified time period af- hose connecting it to the air cleaner housing, pro-ter hot starts, the PCM grounds the EVAP canister vides the source of air for system.purge solenoid causing it to energize. This will pre- The positive crankcase ventilation (PCV) systemvent vacuum from reaching the EVAP canister valve. operates by engine intake manifold vacuum (Fig. 9).When the engine reaches an operating temperature Filtered air is routed into the crankcase through theof approximately 60°C (140°F), the PCM removes the air cleaner hose and crankcase breather/filter. Thisground to the solenoid. The de-energized solenoid forces crankcase vapors through the PCV valve. It isthen allows vacuum to flow to the EVAP canister and then drawn into the intake manifold. Here it be-purge fuel vapors through the intake manifold and comes part of the calibrated air/fuel mixture to be
  • 8. 25 - 8 EMISSION CONTROL SYSTEMS ZJ Fig. 7 CCV System—4.0L Engine—Non-California System Shownconsumed in the combustion chamber. The PCV sys- POSITIVE CRANKCASE VENTILATION (PCV)tem constantly ventilates the crankcase to help pre- VALVEvent sludge formation and vapors from entering the The PCV valve contains a spring loaded plunger.atmosphere. This plunger meters the amount of crankcase vapors routed into the combustion chamber based on intake manifold vacuum. When the engine is not operating, or during an en- gine popback, the spring forces the plunger back against the seat. This will prevent vapors from flow- ing through the valve (Fig. 10). Fig. 8 PCV Valve/Hose—5.2L Engines Fig. 9 Typical Closed Crankcase Ventilation System
  • 9. ZJ EMISSION CONTROL SYSTEMS 25 - 9 Fig. 10 Engine Off or Engine PopBack—No Vapor Flow During periods of high manifold vacuum, such asidle or cruising speeds, vacuum is sufficient to com-pletely compress spring. It will then pull the plungerto the top of the valve (Fig. 11). In this position thereis minimal vapor flow through the valve. Fig. 13 Check Vacuum at PCV Valve—Typical force. This will be after allowing approximately one minute for crankcase pressure to reduce. Fig. 11 High Intake Manifold Vacuum—Minimal Vapor Flow During periods of moderate manifold vacuum, theplunger is only pulled part way back from inlet. Thisresults in maximum vapor flow through the valve(Fig. 12). Fig. 12 Moderate Intake Manifold Vacuum— Fig. 14 Check Vacuum at Crankcase Breather Maximum Vapor Flow Opening—TypicalINSPECTION AND SERVICE PROCEDURE (4) Turn engine off and remove PCV valve from (1) With engine idling, remove the PCV valve from cylinder head (valve) cover. The valve should rattlecylinder head cover. If the valve is not plugged, a when shaken (Fig. 15).hissing noise will be heard as air passes through the Replace the PCV valve and retest the system if itvalve. Also, a strong vacuum should be felt at the does not operate as described in the preceding tests.valve inlet (Fig. 13). Do not attempt to clean the old PCV valve. (2) Install the PCV valve. Remove the crankcase (5) If the paper is not held against the opening inbreather/filter. Hold a piece of stiff paper, such as a cylinder head (valve) cover after new valve is in-parts tag, loosely over the opening of crankcase stalled, the PCV valve hose may be restricted andbreather/filter at the cylinder head (valve) cover (Fig. must be replaced. The passage in the intake manifold14). must also be checked and cleaned. (3) The paper should be drawn against the opening (6) To clean the intake manifold fitting, turn a 1/4in the cylinder head (valve) cover with noticeable inch drill (by hand) through the fitting to dislodge
  • 10. 25 - 10 EMISSION CONTROL SYSTEMS ZJ Fig. 15 Shake PCV Valve—Typical Fig. 16 Typical Crankcase Breather/Filter—5.2L Engineany solid particles. Blow out the fitting with shop air.If necessary, use a smaller drill to avoid removingany metal from the fitting.CRANKCASE BREATHER/FILTER—5.2L ENGINES The crankcase breather/filter is used with the 5.2LV-8 engine only. The crankcase breather/filter (Fig. 16) is located onthe engine valve cover. It must be kept clean and lu-bricated. At the recommended interval, remove thefilter and wash it thoroughly in kerosene, or similarsolvent. Lubricate or wet the filter by inverting itand filling with SAE 30 engine oil. Filter must thenbe thoroughly drained. More frequent service may benecessary for vehicles operated extensively on shortrun, stop and go, or extended engine idle service. Fig. 17 Pressure Relief/Rollover Valve Location The filter must be replaced at correct intervals. Re-fer to Lubrication and Maintenance, Group 0.PRESSURE RELIEF/ROLLOVER VALVE These vehicles are equipped with a combinationfuel tank pressure relief and rollover valve (Fig. 17).This dual function valve will relieve fuel tank pres-sure and also prevent fuel flow through the fuel tankvent hoses in the event of an accidental vehicle roll-over. The valve incorporates a pressure relief mechanism(Fig. 18) that releases fuel tank pressure when thepressure increases above the calibrated sealing value.Refer to the Fuel Tank section of Group 14, Fuel Sys-tems for removal and installation procedures. Fig. 18 Pressure Relief/Rollover Valve Operation
  • 11. ZJ EMISSION CONTROL SYSTEMS 25 - 11 EXHAUST EMISSION CONTROLS INDEX page pageCatalytic Converter . . . . . . . . . . . . . . . . . . . . . . . . 11 Oxygen (O2S) Sensor . . . . . . . . . . . . . . . . . . . . . . 14EGR (Exhaust Gas Recirculation) System—5.2L Engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11CATALYTIC CONVERTER Refer to Group 11, Exhaust System and Intakemanifold for information.EGR (EXHAUST GAS RECIRCULATION) SYSTEM—5.2L ENGINEGENERAL INFORMATION The Exhaust Gas Recirculation (EGR) System isused with the 5.2L V-8 engine only. The EGR system reduces oxides of nitrogen (NOx)in the engine exhaust and helps prevent sparkknock. This is accomplished by allowing a predeter-mined amount of hot exhaust gas to recirculate anddilute the incoming fuel/air mixture. This dilution re-duces peak flame temperature during combustion. A malfunctioning EGR system can cause enginespark knock, sags or hesitation, rough idle, enginestalling and poor driveability.EGR SYSTEM OPERATION The system consists of: Fig. 1 EGR System Component Location• An EGR valve assembly (Figs. 1 or 2) mounted tothe intake manifold. The EGR valve control also contains an internal• An EGR valve control containing a combination pressure-type transducer (Fig. 2). This transducerback-pressure transducer and an electric vacuum so- portion of the valve control is operated by exhaustlenoid (Figs. 1 and 2). back-pressure from the EGR valve. Exhaust is deliv-• The powertrain control module (PCM) to control ered to the EGR valve through the metal EGR tubethe electric solenoid portion of the valve control. (Fig. 3). This connects it to the rear of the right ex-• An EGR tube (Fig. 3) connecting a passage in the haust manifold. A rubber hose connects the back-intake manifold (near the EGR valve) to the rear of pressure fitting on the EGR valve to the back-the right exhaust manifold. pressure fitting on the valve control (Fig. 2).• Hoses to connect the various components. When the ground signal is removed from the elec- When the PCM removes the ground signal to the tric portion of the valve control (solenoid is not ener-electric solenoid portion of the valve control, EGR gized), and exhaust gas back-pressure entering thesystem operation starts to occur. The PCM will mon- EGR valve inlet is high enough, back-pressure is sup-itor and determine when to supply and remove this plied to the valve control. It then holds the bleedground signal depending on certain engine tempera- valve in the transducer closed. This allows enginetures, throttle positions and other engine operating vacuum to flow through the EGR valve control to ac-conditions. tivate and operate the EGR valve for exhaust gas re- If the electrical connector to the EGR valve circulation. If back-pressure is not strong enough tocontrol (solenoid) is disconnected, or the elec- close the bleed valve in the transducer, the valve con-trical signal is lost, the EGR valve will operate trol will bleed off engine vacuum preventing EGRat all times. This may result in; poor engine perfor- valve operation.mance, rough idle speed and reduced driveability The transducer measures and uses this exhaustduring certain operating conditions. back-pressure signal from the EGR valve to regulate
  • 12. 25 - 12 EMISSION CONTROL SYSTEMS ZJ • The powertrain control module (PCM) determines that EGR system operation is necessary. • The electrical portion of the EGR valve control is not energized (grounded) by the PCM. • Exhaust back-pressure entering the transducer in the EGR valve control is strong enough to close its bleed valve. • Engine vacuum is passed through the EGR valve control to the EGR valve. • The inlet seat (poppet valve) at the bottom of the EGR valve opens to dilute and recirculate exhaust gas back into the intake manifold. For more information, also refer to Open Loop/ Closed Loop Modes of Operation in Group 14, Fuel Systems. EGR GAS FLOW TEST Use the following test procedure to determine if ex- haust gas is flowing through the EGR valve. It can also be used to determine if the EGR tube is plugged, or the system passages in the intake or exhaust man- ifolds are plugged. This is not to be used as a complete test of the EGR system. The engine must be started, running and warmed to operating temperature for this test. (1) All engines are equipped with two fittings lo- Fig. 2 EGR Valve and EGR Valve Control cated on the EGR valve (Fig. 4). The upper fitting (located on the vacuum motor) supplies engine vac- uum to a diaphragm within the EGR valve for valve operation. The lower fitting (located on the base of the EGR valve) is used to supply exhaust back-pres- sure to the EGR valve control. Fig. 3 EGR Tubeand provide the correct amount of exhaust gas recir-culation under all conditions. Exhaust gas recirculation will begin in this orderwhen: Fig. 4 Typical EGR Valve
  • 13. ZJ EMISSION CONTROL SYSTEMS 25 - 13 (2) Disconnect the rubber hose at the vacuum mo- nostic Procedures service manual for operation of thetor fitting (Fig. 4) on the top of the EGR valve vac- DRB scan tool when diagnosing the EGR system.uum motor. (3) Connect a hand-held vacuum pump to this fit-ting. (4) Start the engine. (5) Slowly apply 5 inches of vacuum to the fittingon the EGR valve motor. (6) While applying vacuum, and with the enginerunning at idle speed, the idle speed should drop orthe engine may even stall. This is indicating that ex-haust gas is flowing through the EGR tube betweenthe intake and exhaust manifolds. (7) If the engine speed did not change, the EGRvalve may be defective, the EGR tube may beplugged with carbon, or the passages in the intakeand exhaust manifolds may be plugged with carbon. (a) Remove EGR valve from engine. Refer to EGR Valve Removal in this group. (b) Apply vacuum to the vacuum motor fitting and observe the stem on the EGR valve. If the stem is moving, it can be assumed that the EGR valve is functioning correctly. The problem is in ei- ther a plugged EGR tube or plugged passages at the intake or exhaust manifolds. Refer to step (c). Fig. 5 Data Link Connector—Typical Location If the stem will not move, replace the EGR valve. (6) After checking the system with the DRB scan Note: The EGR valve, valve control and attaching tool, proceed to the following: EGR Valve Leakage hoses are serviced as one unit. Refer to EGR Valve Test, or EGR Valve Control Test and repair as neces- Removal/Installation in this group. sary. (c) Remove the EGR tube between the intake and exhaust manifolds. Check and clean the EGR EGR VALVE LEAKAGE TEST tube and its related openings on the manifolds. Re- This is not to be used as a complete test of the fer to EGR Tube in this group for procedures. EGR system. Do not attempt to clean the EGR valve. If the valve If the engine will not idle, dies out on idle, or idleshows evidence of heavy carbon build-up near the is rough or slow, the poppet valve (Fig. 2) at the basebase, replace it. of the EGR valve may be leaking in the closed posi-EGR SYSTEM TEST tion. The diaphragm (Fig. 2) within the EGR valve may also be ruptured.WARNING: APPLY PARKING BRAKE AND/OR (1) The engine should be off for the following test.BLOCK WHEELS BEFORE TESTING THE EGR SYS- (2) Disconnect the rubber hose from the fittingTEM. (Fig. 2) at the top (vacuum motor) side of the EGR valve. (1) Warm up the engine and bring to operating (a) Connect a hand-held vacuum pump to thistemperature before performing the proceeding tests. fitting. (2) Check the condition of all EGR system hoses (b) Apply 15 inches of vacuum to the pump.and tubes for leaks, cracks, kinks and hardening of (c) Observe the gauge reading on the pump.rubber hoses. Repair and correct these conditions be- (d) If vacuum falls off, the diaphragm in thefore performing any tests. EGR valve has ruptured. (3) Be sure the hoses at both the EGR valve and (e) Replace the EGR valve. Note: The EGR valve,EGR valve control are connected to the proper fit- valve control and attaching hoses are serviced astings. Refer to figure 2. one unit. Refer to EGR Valve Removal/Installation (4) Be sure the electrical connector is firmly con- in this group.nected at the valve control. (f) If vacuum did not fall off, proceed to the next (5) To check EGR system operation, connect the step.DRB scan tool to the data link connector. The data (3) A small metal fitting (back-pressure fitting) islink connector is located in the engine compartment located at the base of the EGR valve (Fig. 2). A rub-(Fig. 5). Refer to the appropriate Powertrain Diag- ber back-pressure hose connects it to the back-pres-
  • 14. 25 - 14 EMISSION CONTROL SYSTEMS ZJsure fitting on the EGR valve control. Disconnect this (7) Remove the rubber hose at the vacuum inletrubber hose at the EGR valve fitting. fitting (Fig. 2) on the EGR valve control. (4) Remove the air intake tube at the throttle body. (8) Connect a vacuum gauge to this disconnected (5) Using compressed air, and using an air nozzle hose.with a rubber tip, apply approximately 50 psi of reg- (9) Start the engine and bring to operating temper-ulated shop air to the metal back-pressure fitting on ature. Hold engine speed at approximately 1500 rpm.the EGR valve. (10) Check for steady engine vacuum (full-mani- (6) By hand, open the throttle to the wide open po- fold) at this hose.sition. Air should not be heard emitting from the (11) If engine vacuum (full-manifold) is notintake manifold while applying air pressure at the present, check vacuum line to engine and repair asback-pressure fitting. necessary before proceeding to next step. (7) If air can be heard emitting from the intake (12) Reconnect the rubber hose to the vacuum in-manifold, the poppet valve (Fig. 2) is leaking at the let fitting (Fig. 2) on the EGR valve control.bottom of the EGR valve. Replace the EGR valve. (13) Disconnect the rubber hose at the vacuumNote: The EGR valve, valve control and attaching outlet fitting (Fig. 2) on the EGR valve control.hoses are serviced as one unit. Refer to EGR ValveRemoval/Installation in this group. Do not attempt (14) Connect a vacuum gauge to this fitting.clean the old EGR valve. (15) Disconnect the electrical connector (Fig. 1) at the valve control. This will simulate an open circuitEGR VALVE CONTROL TEST (no ground from the PCM) at the valve control. (16) Start the engine and bring to operating tem-TESTING ELECTRICAL SOLENOID PORTION OF VALVE perature.CONTROL Hold the engine speed to approximately 2000 rpm This is not to be used as a complete test of the while checking for engine vacuum (full-manifold) atEGR system. this fitting. To allow full manifold vacuum to Electrical operation of the valve control should be flow through the valve control, exhaust back-checked with the DRB scan tool. Refer to the appro- pressure must be present at valve control. Itpriate Powertrain Diagnostic Procedures service must be high enough to hold the bleed valve inmanual for operation of the DRB scan tool. Replace the transducer portion of the valve controlsolenoid (valve control) if necessary. closed. Have a helper momentarily (a second or two)TESTING VACUUM TRANSDUCER PORTION OF VALVE hold a rag over the tailpipe opening to build some ex-CONTROL haust back-pressure while observing the vacuum The first part of this test will determine if the gauge. Heavy gloves should be worn. Do not covertransducer diaphragm at the back-pressure side of the tailpipe opening for an extended period ofthe valve control has ruptured or is leaking. The sec- time as damage to components or overheatingond part of the test will determine if engine vacuum may result.(full-manifold) is flowing from the inlet to the outlet As temporary back-pressure is built, full manifoldside of the valve control. This is not to be used as a vacuum should be observed at the vacuum controlcomplete test of the EGR system. outlet fitting. Without back-pressure, and engine at (1) Electrical operation of the valve control should approximately 2000 rpm, the gauge reading will befirst be checked with the DRB scan tool before pro- low. This low reading is normal. At idle speed, theceeding with the vacuum test. Refer to the appropri- gauge reading will be erratic. This is also normal.ate Powertrain Diagnostic Procedures service manual (17) If full manifold vacuum is not present at thefor operation of the DRB scan tool. outlet fitting, but was present at the inlet fitting, re- (2) Disconnect the rubber back-pressure hose from place the valve control. Note: The EGR valve, valvethe fitting at the bottom of EGR valve control (Fig. control and attaching hoses are serviced as one unit.2). Refer to EGR Valve Removal/Installation in this (3) Connect a hand-held vacuum pump to this fit- group.ting. (4) Apply 10 inches of vacuum to this fitting. OXYGEN (O2S) SENSOR (5) If vacuum falls off, the valve control diaphragm For description, operation, diagnosis and removal/is leaking. (6) Replace the EGR valve control. Proceed to next installation procedures of the O2S sensor, refer tostep for further testing. Group 14, Fuel Systems.
  • 15. ZJ EMISSION CONTROL SYSTEMS 25 - 15 COMPONENT REMOVAL/INSTALLATION INDEX page pageAir Cleaner Element . . . . . . . . . . . .. . . . . . . . . . . 15 EVAP Canister Purge Solenoid . . . . ..... .. . . . . 17Air Cleaner Housing . . . . . . . . . . . .. . . . . . . . . . . 15 EVAP Canister Purge Solenoid—Duty Cycle . . . . . 17EGR Tube—5.2L Engine . . . . . . . . .. . . . . . . . . . . 15 Fuel Tank Filler Tube Cap . . . . . . . . ..... .. . . . . 18EGR Valve Control . . . . . . . . . . . . .. . . . . . . . . . . 16 Oxygen (O2S) Sensor . . . . . . . . . . . ..... .. . . . . 18EGR Valve—5.2L Engine . . . . . . . .. . . . . . . . . . . 15 Powertrain Control Module (PCM) . . ..... .. . . . . 18Engine Coolant Temperature Sensor . . . . . . . . . . . 15 Pressure Relief/Rollover Valve . . . . . ..... .. . . . . 18EVAP Canister . . . . . . . . . . . . . . . .. . . . . . . . . . . 16AIR CLEANER HOUSING Refer to either of the Component Removal/Installa-tion sections of Group 14, Fuel System for proce-dures.AIR CLEANER ELEMENT Refer to either of the Component Removal/Installa-tion sections of Group 14, Fuel System for proce-dures.ENGINE COOLANT TEMPERATURE SENSOR For description, operation, diagnosis and removal/installation procedures, refer to the 4.0L or 5.2L sec-tions of Group 14, Fuel Systems.EGR VALVE—5.2L ENGINEREMOVAL The EGR valve, EGR valve control (solenoid) andattaching hoses are serviced as one unit on the 5.2Lengine. (1) Disconnect vacuum hoses to EGR valve and Fig. 1 EGR Valve Location—5.2L EnginesEGR valve control. Note position of hoses for easierinstallation. (2) Remove the right exhaust manifold heat shield (2) Remove EGR mounting bolts (Figs. 1 or 2). nuts/bolts and remove heat shield (Fig. 3). (3) Remove EGR valve and gasket. Discard old (3) Disconnect 2 hoses at EGR valve. Note positiongasket. Clean intake manifold mating surface and of hoses at EGR valve before removal.check for cracks. (4) Disconnect electrical connector and hoses at EGR valve control. Note position of hoses before re-INSTALLATION moval. (1) Place new EGR gasket on intake manifold. (5) Remove 2 EGR valve mounting bolts (Fig. 2) (2) Install EGR valve. Tighten mounting bolts to and remove EGR valve. Discard old EGR gasket.23 N⅐m (200 in. lbs.) torque. (6) Disconnect electrical connector at engine oil (3) Connect vacuum hoses to EGR valve and EGR pressure sending unit.valve control. (7) To prevent damage to oil pressure sending unit, a special tool, such as number C-4597 must be usedEGR TUBE—5.2L ENGINE (Fig. 4). Remove sending unit from engine. (8) Loosen EGR tube mounting nut at intake man-REMOVAL ifold (Fig. 2). (1) Remove the spark plug cable loom and spark (9) Remove 2 EGR tube mounting bolts at exhaustplug cables from valve cover mounting stud at rear of manifold (Fig. 2) and remove EGR tube. Discard oldright valve cover (Fig. 2). Position spark plug cables gasket at exhaust manifold.to top of valve cover. (10) Remove EGR tube from vehicle.
  • 16. 25 - 16 EMISSION CONTROL SYSTEMS ZJ Fig. 2 EGR Valve Mounting Bolts—5.2L Engines Fig. 4 Oil Pressure Sending Unit—Removal/ Installation—5.2 L Engine (5) Install a new EGR valve gasket at intake man- ifold. (6) Install EGR valve to intake manifold. Tighten 2 EGR bolts to 23 N⅐m (200 in. lbs.) torque. (7) Position EGR valve control and install its elec- trical connector. Connect hoses between EGR valve and EGR valve control. (8) Install spark plug cable loom and spark plug cables to valve cover mounting stud. (9) Install heat shield at right exhaust manifold. EGR VALVE CONTROL The EGR valve, the EGR valve control (solenoid) and the connecting hoses are serviced as one unit on Fig. 3 Exhaust Manifold Heat Shield—5.2L Engine the 5.2L engine. Refer to EGR Valve Removal/Instal-INSTALLATION lation for procedures. (1) Clean the EGR tube and exhaust manifold (atEGR tube mounting point) of any old gasket mate- EVAP CANISTER The EVAP canister is located in the left front cor-rial. ner of vehicle below the left front headlamp (Figs. 5 (2) Install a new gasket to exhaust manifold end of or 6).EGR tube and install EGR tube to both manifolds.Tighten tube mounting nut at intake manifold. REMOVALTighten 2 mounting bolts at exhaust manifold to 23 (1) Remove the grill. Refer to Group 23, Body.N⅐m (204 in. lbs.) torque. (2) Remove the front bumper/fascia assembly. Re- (3) Coat the threads of the oil pressure sending fer to Group 23, Body.unit with thread sealant. Do not allow any of the (3) Disconnect vacuum lines at canister.thread sealant to get into the sending unit opening, (4) Remove the three canister mounting nuts (Figs.or the opening at the engine. Install sending unit to 5 or 6).engine and tighten to 14 N⅐m (130 in. lbs.) torque. In- (5) Lower the canister through bottom of vehicle.stall electrical connector to sending unit. (4) Clean the intake manifold and EGR valve of INSTALLATIONany old gasket material. (1) Position canister to body.
  • 17. ZJ EMISSION CONTROL SYSTEMS 25 - 17 Fig. 5 Canister Location—Non-California Fig. 7 Purge Solenoid—4.0L Engine—California Emission Package REMOVAL (1) Disconnect the electrical connector at the sole- noid (Fig. 7). (2) Disconnect the vacuum lines at the solenoid. (3) Remove the two bracket mounting nuts and re- move solenoid. INSTALLATION (1) Position the solenoid to vehicle. (2) Install and tighten the two bracket mounting nuts. (3) Connect the vacuum lines to the solenoid. (4) Connect the electrical connector to the solenoid. EVAP CANISTER PURGE SOLENOID REMOVAL—5.2L ENGINE (1) Remove air duct at throttle body. Fig. 6 Canister Location—California Emission (2) Disconnect wiring connector at solenoid (Fig. 8). Package—4.0L Only (3) Disconnect vacuum harness at solenoid (Fig. 8). (2) Install canister mounting nuts. Tighten nuts to (4) Remove solenoid and its support bracket from6 N⅐m (55 in. lbs.) torque. intake manifold. (3) Connect vacuum lines. (5) Remove EVAP canister purge solenoid from en- (4) Install the front bumper/fascia assembly and gine.grill. Refer to Group 23, Body. INSTALLATIONEVAP CANISTER PURGE SOLENOID—DUTY CYCLE (1) Install EVAP canister purge solenoid and its mounting bracket to intake manifold.4.0L ENGINE—CALIFORNIA EMISSION (2) Connect vacuum harness and wiring connector.PACKAGE ONLY (3) Install air duct to throttle body. The solenoid is located near the front of the wind-shield washer reservoir bottle (Fig. 7).
  • 18. 25 - 18 EMISSION CONTROL SYSTEMS ZJ OXYGEN (O2S) SENSOR For description, operation, diagnosis and removal/ installation procedures of the O2S sensor, refer to Group 14, Fuel Systems. POWERTRAIN CONTROL MODULE (PCM) For removal and installation procedures, refer to Group 14, Fuel Systems. PRESSURE RELIEF/ROLLOVER VALVE For removal and installation procedures, refer to the Fuel Tank section of Group 14, Fuel Systems.Fig. 8 EVAP Canister Purge Solenoid—5.2L EngineFUEL TANK FILLER TUBE CAP If replacement of the fuel tank filler tube cap (fueltank cap) is necessary, it must be replaced with anidentical cap to be sure of correct system operation.

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