BMW Coupes and Sedans 1970-1988 Repair Guide

Exhaust Gas Recirculation (EGR) System

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See Figure 1



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Fig. Fig. 1: Example of a 4-cylinder engine EGR system

OPERATION



The EGR valve is vacuum operated by the position of the carburetor or injection system throttle plate in the throttle bore during vehicle operation. A metered amount of exhaust gas enters the combustion chamber to be mixed with the air/fuel blend. The effect is to reduce the peak combustion temperatures, which in turn reduces the amount of nitrous oxides (NO 2 ), formed during the combustion process.

TESTING



EGR Valve
2002 AND 3.0 MODELS

Remove the air filter and adjust the engine idle to 900 rpm. Remove the vacuum line from the valve and using an engine vacuum source, attach the hose to the vacuum nipple. The engine speed should drop 500-600 rpm if the valve is operating properly. If little or no change of engine speed is noted, the recirculation pipes, the cyclone filter or the EGR valve may be plugged or defective.

318i AND 320i MODELS
  1. Start the engine and let it idle. Disconnect the blue hose at the EGR valve, and leave both ends open. The engine speed should remain the same. If the engine speed changes, the throttle blade opens too far at idle or the EGR valve is sticking open.
  2.  
  3. Leave the blue hose detached and disconnect the black hose at the intake header. Detach the red hose at the throttle housing and connect it to the open port on the intake header. The engine speed should drop considerably, or the EGR valve is defective and must be replaced.
  4.  
  5. Detach the black hose the header. Detach the red hose at the temperature sensing valve and connect it to the open port on the intake header. If the engine speed drops, the EGR valve is sticking open or the pressure converter is defective. To check the pressure converter, detach red and blue hoses and check for vacuum at the open converter ports (engine running). If there is no vacuum at the ports, but the white hose to the converter has vacuum, the converter is defective.
  6.  

5 SERIES MODELS
  1. With the engine idling and hot, disconnect the black hose at the tee leading into the vacuum control valve.
  2.  
  3. Disconnect the hose at the vacuum limiter, and connect its open end with the open end of the black hose. The engine speed should drop about 100 rpm. Reconnect the black hose to the tee.
  4.  
  5. Disconnect the blue hose at the vacuum control valve and connect its open end to the open end of the hose disconnected from the vacuum limiter in Step 2.The engine speed should now drop about 200 rpm. If either test is failed, replace the EGR valve.
  6.  

6 AND 7 SERIES MODELS
  1. Bring the engine to operating temperature at idle speed. Detach the blue hose at the EGR valve, do not plug either the open end or the hose or the fitting on the valve. The engine speed should stay the same. If the engine speed should stay the same. If the engine speed drops, check the red hose from the throttle housing for vacuum. If there is vacuum there, adjust the idle position of the throttle. If there is no vacuum, the EGR valve is defective.
  2.  
  3. Detach the blue hose at the EGR valve. On 6 Series models, remove the plug from the intake collector, On the 733i, disconnect the white hose at the collector. Pull the red hose off the throttle housing and attach it to the open fitting on the intake collector. If the engine speed does not drop considerably, the EGR valve, coolant temperature switch, or red electric switching valve is defective. If the engine speed does drop, go to Step 5.
  4.  
  5. To test the coolant temperature switch, turn on the engine with the engine stopped and cold _ temperature below 113°F (45°C). Pull the connector plug off the red magnetic valve and connect the test lamp between the 2 open terminals on the valve. The test lamp should not come on. If the test lamp does come on, test the speed switch as described in the next step.
  6.  
  7. To test speed switch, remove the electrical connector from the blue switching valve with the engine idling. Connect a test lamp between the 2 leads. If not, make sure the valve is properly grounded and, if so, replace the speed switch. If the engine speed did not drop in Step 2, and you have made tests described in Steps 3 and 4, test the red cap electric control valve (see below) before condemning the EGR valve.
  8.  
  9. Connect the blue hose back to the EGR valve. Leave the red hose connected as in Step 2. Engine speed should have dropped slightly from normal idle. If the idle speed drops considerably from the normal idle, there are leaking hoses, a defective pressure converter, or a bad EGR valve. Restore all hoses to their normal positions. Check for leaks. If there are no leaks, detach the red hose at the pressure converter with the engine idling and hot. There should be back pressure. Then, detach the white hose to make sure there is intake vacuum. Repair broken or loose red or white hoses, if necessary. Then, reinstall the white hose, pull off the blue hose, and check for vacuum at the blue pressure converter connection. If there is no vacuum, replace the pressure converter; otherwise, replace the EGR valve.
  10.  

REMOVAL & INSTALLATION



EGR Valve
  1. Note the color coding of vacuum hoses and disconnect them.
  2.  
  3. On 320i models, loosen the clamp and disconnect the hose running into the side of the valve.
  4.  
  5. Unscrew the nut at the bottom of the valve with a spanner wrench. On 6 cylinder engines, remove the 2 mounting bolts for the EGR valve holding bracket, from the intake pipes, and pull the valve free of the recirculation hose.
  6.  

To install:
  1. Install the valve to the hose and install the retaining bolts.
  2.  
  3. Screw in the nut at the bottom of the valve and connect the vacuum hoses. On 320i models, connect the hose to the side of the valve and tighten the clamp.
  4.  

Electric Control Valve
5, 6 AND 7 SERIES MODELS

On models equipped, the electric control valve should stop the EGR valve operation at coolant temperatures below 113°F (45°C), and speeds above 3000 rpm. Tag and disconnect both vacuum hoses at the control valve with the engine off and the coolant temperature below 113°F (45°C). Connect a test hose to one of the nipples and blow through the hose. The valve is functioning properly when there is air flowing through the valve with the ignition OFF and no air flow through the valve with the ignition ON .

Connect the vacuum hoses to the valve and operate the engine until the coolant is heated over 113°F (45°C). Disconnect the hoses and check for air flow through the valve. Air should now flow through the valve.

Coolant Temperature Switch and Control Relay
  1. With the coolant temperature below 113°F (45°C), turn the ignition ON , but do not start the engine. Remove the wire plug at the control valve and connect a test lamp to the plug.
    1. The test lamp should light. If the test lamp does not light, connect the test lamp to ground. If the lamp now operates, the ground wire to the control valve has an open circuit.
    2.  
    3. If the test lamp still does not light, disconnect the wire terminal at the coolant temperature switch and connect it to ground. If the test lamp still does not light, replace the control valve.
    4.  

  2.  
  3. With the coolant temperature above 113°F (45°C), turn the ignition switch ON but do not start the engine. Disconnect the wire terminal plug at the control valve and connect a test lamp. The lamp should be off. If the lamp is on, the coolant temperature switch or control relay is defective.
  4.  
  5. With the engine running at temperatures above 113°F (45°C), connect the test light to the disconnected plug of the control light to the disconnected plug of the control valve. The test lamp should be on over an engine speed of 3000 rpm. If the test lamp does not light, the speed switch is defective.
  6.  

REMOVAL & INSTALLATION



EGR Filter

See Figure 2

The EGR filter should be replaced every 25,000 miles (40,000). The exhaust system should be cool before replacing.

  1. Detach all lines.
  2.  
  3. Loosen the hold-down bolts.
  4.  



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Fig. Fig. 2: Example of an EGR filter

  1. Remove the bolts and filter.
  2.  
  3. Installation is the reverse of removal.
  4.  

EGR Warning Light

See Figure 3

A warning light marked EGR is triggered at 25,000 miles (40,000 km) intervals, to alert the driver to service the exhaust gas recirculation system filter.

A triggering device, located under the dash and driven by the speedometer cable, can be reset to open the electrical contracts and extinguish the EGR warning light.

Two different sized buttons are mounted side-by-side on the triggering device. The small button is for the reactor light and the large button is for the EGR light. Press the button to reset.



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Fig. Fig. 3: EGR and thermal reactor triggering box, mounted in the engine compartment. The thermal reactor reset button (1) and EGR reset button (2) can be pressed with the eraser end of a pencil

 
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