Mitsubishi Pick-ups and Montero 1983-1995 Repair Guide

Exhaust Gas Recirculation (EGR) System

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OPERATION



See Figure 1

Exhaust Gas Recirculation (EGR) is used to reduce peak flame temperatures in the combustion chamber. A small amount of exhaust gas is diverted from the exhaust manifold and re-entered into the intake manifold, where it mixes with the air/fuel charge and enters the cylinder to be burned. Cooler combustion reduces the formation of Nitrogen Oxide (NO 2 ) emissions.

The system consists of the EGR valve, controlling the flow of exhaust gas and various vacuum and/or electric controls to keep the EGR from working at the incorrect time.

No EGR is required when the engine is cold due to lower flame temperatures in the engine. EGR under these conditions would produce rough running so EGR function is cut off either by a thermo valve or by the ECM (which is monitoring coolant temperature.) Additionally, EGR flow is cut off at warm idle to eliminate any roughness or stumble on initial acceleration.

Cooler combustion temperatures also result in slightly reduced power output. This isn't felt during normal, part-throttle driving and the emission benefits outweigh the slight loss. However, in a wide-open throttle situation a power reduction is not desirable; full power could be the margin of success in a passing or accident avoidance situation. For this reason, EGR function is eliminated when the engine goes on wide-open throttle. Normally, the vacuum to the EGR valve can overcome the spring tension within the valve and hold it open. When the throttle opens fully, vacuum to the EGR is reduced and the spring closes the valve.

A common symptom of EGR malfunction is light engine ping at part throttle, particularly noticeable under load such as going uphill or carrying several passengers. An EGR valve which fails to close properly can also cause a rough or uneven idle. If the engine is correctly tuned and other common causes (vacuum leaks, bad plug wires, etc.) are eliminated, EGR function should be considered as a potential cause when troubleshooting a rough idle.

Since the majority of EGR components do not require routine maintenance and should not clog or corrode if unleaded gas is used, you should check all other reasonable causes of a problem before checking this system.



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Fig. Fig. 1: A diagram of a common EGR system-2.0L and 2.6L engines

TESTING



A vacuum pump capable of producing more than 10 in. Hg. (33.8 kPa) of vacuum will be needed to perform this test.

EGR System

See Figures 2 and 3

2.0L AND 2.6L ENGINES
  1. Allow the engine to cool overnight. Since the EGR system works differently for warm and cold engines, a completely cold engine is required for testing.
  2.  
  3. Disconnect the vacuum hose with the green stripe from either the throttle body (fuel injected) or the base of the carburetor. Attach the end of the hose to vacuum pump.
  4.  
  5. Plug the port from which the hose was removed. Start the engine and attempt to draw a vacuum with the hand pump. The system should NOT hold vacuum with the engine cold and running at idle.
  6.  
  7. Allow the engine to warm up to normal operating temperature. The coolant must be 80-85°C (175-185°F) before testing. Using the pump, draw a vacuum of 1.2-1.7 in. Hg (4-5.75 kPa). The carbureted system will leak vacuum at warm idle.
  8.  
  9. For carbureted engines, increase the engine speed to 3500 rpm. Slowly draw vacuum with the hand pump and observe the vacuum gauge on the pump. The system should leak vacuum until the pump reaches about 1.5 in. Hg, (5.75 kPa) at which time the vacuum should be held.
  10.  



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Fig. Fig. 2: Check the EGR system vacuum by using a hand vacuum pump and a "T" connector



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Fig. Fig. 3: Disconnect the three-way terminal (the "T"), and connect the hand vacuum pump to the EGR valve

2.4L, 3.0L AND 3.5L ENGINES



  1. Allow the engine to cool overnight.
  2.  
  3. Disconnect the vacuum hose with the green stripe from the EGR valve. Use a "T" connector to connect the hand vacuum pump into the system and connect the hose back to the EGR.
  4.  
  5. Start the engine and observe the vacuum gauge on the hand pump. Press the accelerator suddenly to race the engine. On a cold engine, there should be no change in the vacuum; normal (atmospheric) pressure is maintained.
  6.  
  7. Allow the engine to warm up to normal operating temperature, generally 158-170°F (68-77°C). Repeat the sudden rpm test while watching the gauge on the pump. The vacuum should rise temporarily to about 3.9 in. Hg (13.2 kPa).
  8.  
  9. Disconnect the "T" from the system and connect the vacuum pump directly to the EGR valve.
  10.  
  11. Draw a vacuum of at least 9.4 in. Hg (31.75 kPa) for the 2.4L and the 3.0L (12 valve) engines or 9.1 in. Hg (30.7 kPa) for the 3.0L (24 valve) and 3.5L engines while the engine is at warm idle. The quality of the idle should change noticeably, becoming rough or even stalling as the EGR valve opens. The exact vacuum level at which this occurs varies by engine family.
  12.  

EGR Valve Control Vacuum

Coolant temperature should be 185-203°F (85-95°C).

  1. Disconnect the vacuum hose from the throttle body EGR vacuum nipple and connect a hand vacuum pump to the nipple.
  2.  
  3. Start the engine and check to see that, after raising the engine speed by racing the engine, vacuum raises proportionately with the rise in engine speed.
  4.  

If there is a problem with the change in vacuum, it is possible that the throttle body port may be clogged and requires cleaning.

  1. Reconnect the vacuum hoses.
  2.  

EGR Valve

See Figure 4

  1. Label and disconnect the hoses from the valve. Carefully loosen and remove the retaining bolts, remembering that they are probably heat-seized and rusty. Use penetrating oil freely.
  2.  
  3. Remove the valve and clean the gasket remains from both mating surfaces.
  4.  
  5. Inspect the valve for any sign of carbon deposits or other cause of binding or sticking. The valve must close and seal properly; the pintle area may be cleaned with solvent to remove soot and carbon.
  6.  
  7. Attach the vacuum pump to the vacuum port on the EGR valve. If the valve has two vacuum ports, pick one and plug the other.
  8.  
  9. Perform the vacuum holding test. Refer to the following information and draw the correct amount of vacuum, making sure it is held. If the correct vacuum cannot be maintained, the valve is leaking internally.

    2.0L and 2.6L engines: holds vacuum at 10 in. Hg (33.75 kPa), will not pass air at 1.2 in. Hg (4 kPa), air passes through at 3.3 in. Hg (11.2 kPa).
     
    3.0L 1989 engines: holds vacuum at 9.7 in. Hg (32.75 kPa), will not pass air at 0.8 in. Hg (2.7 kPa), air passes through at 3.3 in. Hg (11.2 kPa).
     
    2.4L, 3.0L and 3.5L post 1990-95 engines: will not pass air at 1.2 in. Hg (4 kPa) or less, air passes through at 9.1-9.4 in. Hg (30.7-31.75 kPa) or more.
     

  10.  



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Fig. Fig. 4: Use the hand vacuum pump to check the functioning of the EGR valve

  1. Release the vacuum but keep the pump attached to the valve. Devise a way to blow into the valve while drawing a vacuum and reading the gauge on the pump. Draw a slight vacuum and make sure that the valve is closed (your breath does not pass) at the specified vacuum.
  2.  
  3. Now increase the vacuum and check that the valve passes air at the specified vacuum. If the valve is sticky or worn, it may not open properly. A weakened valve will open too soon. If either condition is encountered, replace the valve.
  4.  
  5. Install the valve with a new gasket. (Don't forget to remove the plug from the second vacuum port). Tighten the bolts.
  6.  
  7. Connect the hoses and lines to their proper ports.
  8.  

EGR Control Solenoid

See Figures 5, 6 and 7

  1. Label and disconnect the vacuum hoses, taking note of the position of each.
  2.  
  3. Remove the wiring harness connector.
  4.  
  5. Connect the hand vacuum pump to the port which contained the vacuum hose with the red stripe (green stripe on 1990-95 2.4L, 3.0L and 1994-95 3.5L engines).
  6.  
  7. Use jumper wires to bridge battery voltage to the terminals of the solenoid.Draw a vacuum with the pump. When battery voltage is present, the solenoid should hold vacuum. When the voltage is removed, it should not be possible to draw and hold a vacuum. If either condition is not met, the unit must be replaced.
  8.  



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Fig. Fig. 5: Connect the hand vacuum pump to the nipple where the green-stripped vacuum hose was attached



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Fig. Fig. 6: Apply a vacuum and check to see if vacuum is maintained when a 12 volt current is supplied-be certain to connect the wires to the correct terminals



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Fig. Fig. 7: Measure the resistance between the terminals of the solenoid valve-the resistance should be 36-44 ohms at 20°C (68°F)

Thermo Valve

A vacuum pump capable of producing more than 10 in. Hg (33.8 kPa) of vacuum will be needed to perform this test.

The engine families which contain the secondary air system use the purge control temperature thermovalve to enable or trigger the EGR system. Later engines (G64B, 4G15, 4G61, 4G63 and 6G72) use a separate sensor devoted just to the EGR system.

1990-95 Pick-up trucks and Monteros use an additional sensor which measures the temperature of the exhaust gas at the EGR. The electrical signal generated by this EGR temperature sensor is used in conjunction with the signal from the oxygen sensor to fine tune the air/fuel mixture very accurately under all driving conditions.

The vacuum valve is checked by removing the hoses (label them!) and installing the vacuum pump on one port. Draw a vacuum with the pump: if the coolant temperature is below 122°F (50°C), vacuum should leak. Once the engine is warmed up to its normal operating temperature 175-185°F (80-85°C) the vacuum should be held. If it is necessary to remove the valve, partially drain the coolant until it is below the level of the sensor. Perform this work only on a cold engine. Carefully unscrew the unit, applying wrench force only to the faceted part, never on the plastic. Before reinstalling, coat the threads with sealant (3M®No. 4171 or equivalent); tighten the valve to 22 ft. lbs. (30 Nm) and refill the coolant.

The California electric EGR temperature sensor must be removed from the car before testing. With the motor cold, carefully disconnect the wiring connector and unscrew the sensor from the EGR valve.

Place the sensor in a pan of water. Use a thermometer to measure the water temperature as you heat the pan. Use an ohmmeter to measure the resistance at the terminals of the sensor as the temperature increases. At 50°C (122°F) ) the resistance should be 60,000-83,000 ohms. When the water reaches 212°F (100°C) , the resistance should be 11,000-14,000 ohms. The sensor should be replaced if there is significant deviation in the resistance. When reinstalling the sensor, tighten it to 8 ft. lbs. (11 Nm).

 
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