Jeep Wagoneer/Commando/Cherokee 1984-1998

Exhaust Gas Recirculation (EGR) System

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OPERATION



See Figure 1

NOx (oxides of nitrogen) is a tailpipe emission caused by the oxidation of nitrogen in the combustion chamber. When the peak combustion temperatures go over 2500°F (1371°C) NOx is formed in excessive amounts. To keep the combustion temperatures down, exhaust gas is recirculated.

Recirculation of the exhaust gases is accomplished by having a movable valve between the exhaust and intake manifolds. Upon a predetermined demand, engine vacuum is routed to the valve, opening the connecting port and allowing exhaust gases to enter the intake tract.

The EGR valves used on Jeep vehicles fall into three categories:



An EGR valve with no backpressure sensor which is controlled by ported vacuum only. 2.5L and 2.8L engines are equipped with this type of EGR valve.
 
An EGR valve with an external backpressure sensor which is controlled by ported vacuum and backpressure. 4.0L engines are equipped with this type of EGR valve.
 
An EGR valve with an electric EGR transducer is found on 5.2L engines.
 

Thermal vacuum switches, which control the amount of vacuum available to the EGR valve based on air or water temperature, are used to disable the EGR system before the vehicle reaches operating temperature.



Click image to see an enlarged view

Fig. Fig. 1: Cutaway view of a common EGR valve

COMPONENT TESTING



EGR Solenoid
  1. Start engine and bring to normal operating temperature. Allow engine to idle while performing tests.
  2.  
  3. Check vacuum at solenoid vacuum source hose. Disconnect the hose and attach a vacuum gauge.
  4.  
  5. Vacuum should be 15 in. Hg. (103 kPa), If low, check for leaks, loose fittings or kinks in the line.
  6.  
  7. Check vacuum at solenoid port. Disconnect the line and attach a vacuum gauge.
  8.  
  9. If vacuum reading is zero, go to Step 6. If vacuum is present, check solenoid operation with the Diagnostic Readout Box (DRB II) service tester and repair as necessary.
  10.  
  11. Disengage electrical connector at solenoid. If vacuum is present, proceed to EGR valve test. If not, replace the solenoid.
  12.  

EGR Valve
  1. Leave solenoid electrical connector disengaged. Bypass the vacuum transducer, if equipped, and connect EGR valve solenoid output hose directly to the nipple on the EGR valve.
  2.  
  3. The engine should run roughly or stall. If this occurs, the valve is good. Proceed to the transducer test, for 4.0L engines. If engine rpm does not change, disconnect hose from EGR and connect a hand vacuum pump.
  4.  
  5. Apply 12 in. Hg (82 kPa) of vacuum. If engine runs rough or stalls, inspect vacuum lines in EGR system for leaks and repair as necessary. If no leaks are found, go to transducer test for the 4.0L engine; Step 4 for the other engines.
  6.  
  7. If engine idle still does not change, remove the EGR valve and inspect for a blockage in the intake manifold passage. Repair as necessary. If no blockage is found, replace the EGR valve.
  8.  

Vacuum Transducer

See Figures 2, 3 and 4

This is used on 4.0L engines only.

  1. Disconnect all transducer lines and remove transducer.
  2.  
  3. Plug transducer output port. Apply 1-2 pounds air pressure to transducer backpressure port (used compressed air adjusted to correct pressure). Apply a minimum of 12 in. Hg (kPa) of vacuum to transducer input port.
  4.  
  5. Replace transducer if it will not hold vacuum.
  6.  



Click image to see an enlarged view

Fig. Fig. 2: EGR system with a vacuum transducer



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Fig. Fig. 3: View of a 4.0L engine with an EGR valve and a vacuum transducer



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Fig. Fig. 4: Vacuum transducer port identification

Coolant Temperature Override (CTO) Switch

See Figure 5

  1. Check vacuum lines for leaks and proper routing.
  2.  
  3. Disconnect vacuum line from EGR valve and connect a vacuum gauge.
  4.  
  5. Start engine and ensure that coolant is below 100°F (38°C).
  6.  
  7. Operate engine a 1,500 rpm. There should be no vacuum. If vacuum is present, replace the CTO switch.
  8.  
  9. Allow engine to idle until coolant temperature exceeds 115°F (46°C).
  10.  
  11. Operate the engine at 1,500 rpm. Vacuum should be present. If not, replace the CTO switch.
  12.  



Click image to see an enlarged view

Fig. Fig. 5: EGR system using a coolant temperature override switch

Thermal Vacuum Switch (TVS)
  1. With the engine cold and ambient air temperature in the air cleaner below 40°F (4°C), disconnect the vacuum hoses from the TVS (located on the air cleaner).
  2.  
  3. Connect a hand vacuum pump to the inner port and apply vacuum.
  4.  
  5. Vacuum should be maintained at air cleaner intake temperatures below 40°F (4°C). If vacuum is not held, check to see that temperature is below 40°F (4°C). If so, replace the TVS.
  6.  
  7. Start the engine and warm to normal operating temperature. With an air cleaner intake temperature above 55°F (13°C), the switch should not hold vacuum. If vacuum is held, check to see that temperatures are above 55°F (13°C). If so, replace the TVS.
  8.  

Temperatures are nominal values and the actual switching temperature may vary.

Removal & Installation



EGR Valve

See Figures 6, 7 and 8



Click image to see an enlarged view

Fig. Fig. 6: View of the 2.5L engine EGR valve location

  1. Tag and disengage the vacuum hoses to the EGR valve and the valve control.
  2.  
  3. Remove the EGR retaining bolts, then the valve and gasket.
  4.  

To install:
  1. Clean both mating surfaces and install a new gasket.
  2.  
  3. Install the EGR valve and tighten the retaining bolts to 200 inch. lbs. (23 Nm).
  4.  
  5. Engage the vacuum hoses.
  6.  



Click image to see an enlarged view

Fig. Fig. 7: Removing the EGR valve



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Fig. Fig. 8: Remove and discard the old EGR valve gasket

EGR Tube

See Figures 9 and 10

EXCEPT 5.2L and 5.9L ENGINES
  1. Remove EGR tube-to-exhaust manifold bolts.
  2.  
  3. Unscrew EGR tube line nut at intake manifold. Remove EGR tube.
  4.  
  5. Install EGR tube with a new gasket. Tighten line nut to 30 ft. lbs. (40 Nm) and exhaust manifold bolts to 14 ft. lbs. (18 Nm).
  6.  



Click image to see an enlarged view

Fig. Fig. 9: View of the 2.5L engine EGR tube



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Fig. Fig. 10: View of the 4.0L engine EGR tube

5.2L and 5.9L ENGINES

See Figure 11

  1. Remove the spark plug wire loom and wires from the valve cover. Position the wires to one side.
  2.  
  3. Remove the right exhaust manifold heat shield retainers and the shield.
  4.  
  5. Remove the EGR valve. Refer to the proper procedure in this section.
  6.  
  7. Disengage the oil pressure sending unit electrical connection and remove the sending unit using tool C-4597 or its equivalent.
  8.  
  9. Unfasten the EGR tube nut at the intake manifold and the tube mounting bolts at the exhaust manifold.
  10.  
  11. Remove the EGR tube and gasket. Discard the old gasket.
  12.  

To install:
  1. Clean the EGR tube and exhaust manifold mating surfaces and install a new gasket.
  2.  
  3. Install the EGR tube and engage it to both manifolds. Fasten the nut at the intake manifold and tighten the bolts at the exhaust manifold to 204 inch. lbs. (23 Nm).
  4.  
  5. Coat the threads of the oil pressure sender with a thread sealant and install the sender. Tighten the sender to 130 inch. lbs. (14 Nm).
  6.  
  7. Engage the sender electrical connection.
  8.  
  9. Install the EGR valve. Refer to the proper procedure in this section.
  10.  
  11. Install the right exhaust shield and tighten the retainers.
  12.  
  13. Install the spark plug loom and wires.
  14.  



Click image to see an enlarged view

Fig. Fig. 11: View of the EGR system and related components-1995 5.2L Grand Cherokee model shown

Electric EGR Transducer (EET)
  1. Disengage the EET electrical connector.
  2.  
  3. Tag and disengage the hoses to the EET.
  4.  
  5. Remove the EET from the engine.
  6.  

To install:
  1. Install the EET and engage the hoses.
  2.  
  3. Engage the EET electrical connections.
  4.  

 
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