B. EGR Components
OPERATION EXHAUST GAS RECIRCULATIONB. EGR components
Exhaust manifold
The exhaust manifold is provided with a connection (arrow) for tapping the exhaust gases about to be recirculated.
Corrugated tubing
A corrugated tube is installed between exhaust manifold and EGR valve through which the exhaust gases are routed from exhaust manifold to EGR valve.
EGR valve
The EGR valve is flanged to intake manifold and controls the quantity of the returned exhaust gases depending on operating conditions.
Intake manifold
The intake manifold is provided with a two-hole flange (arrow) for attaching EGR valve. The recirculated exhaust gases are distributed to the individual cylinders.
Vacuum tapping point with orifice (62, color code black)
The vacuum for controlling EGR is taken from vacuum line between vacuum pump and brake booster (arrow). The tapping point has a black orifice (62) with an ID of 0.6 mm (not exchangeable).
Thermovalve 40°C (color code blue)
The thermovalve is screwed into thermostat housing. The designation "50 AB 5" is punched into metal part.
Below 40°C/104°F coolant temperature the bimetallic plate rests against 0-ring and closes connection "B".
Starting at approx. 40°C/104°F coolant temperature the bimetallic plate will snap in downward direction under influence of heat. Both connections are connected to each other.
The vacuum line (white/brown) to distributor should be plugged to connection "B", since this alone will guarantee perfect sealing between bimetallic plate and 0-ring.
Switchover valve (64a, model year 1980)
The switchover valve is switched via guide lever (68) and cam.
The valve serves the purpose of venting the vacuum line to EGR valve for the purpose of switching off EGR at idle (throttle) linkage against idle speed stop).
If the throttle linkage is actuated to the extent that the idle path (L) at idle path rod is bridged, the switchover valve has switched over and the largest possible EGR will proceed.
Switchover valve (64b)
The switchover valve is switched over by the second cam on guide lever (68) shortly before attaining full throttle position. As a result, the vacuum line (white/purple/brown) to EGR valve will be vented and there will be no EGR.
Attention! The link and the cam running surface should be clean and not lubricated. They should be covered during engine preservation.
Note: At idle position (without idle path bridge "L") both switchover valves may have passage from 2 to 5 only. With switchover valves switched through, passage should be available from 3 to 5.
Switchover valves (model year 1981)
To control EGR, the switchover valves known from model year 1980 are used again, but their arrangement has been modified. Both switchover valves are now located on valve plate one above the other. Connection is made by a central plug (71). A cover plate is attached to prevent dirt collecting on plastic running surface.
Orifice (63)
Orifices of different diameter may be installed between the two distributors on vacuum control valve (65).
Color code and diameter of orifices
green 0.7 mm
white 0.8 mm
blue 1.0 mm
red 1.1 mm
yellow 2.0 mm (unthrottled)
The ID of the orifice depends on the tolerances of the adjusting angle on regulating lever (1) of injection pump and vacuum control valve (65).
Vacuum control valve (65)
The vacuum control valve serves to control venting of EGR valve. At idle, the vacuum line to automatic transmission, to thermovalve 40°C/104°F and switchover valve (64a) is constantly vented by way of a small annular gap in vacuum control valve. The vacuum amounts to approx. 350-500 mbar.
After bridging the idle path, the vent cross section in vacuum control valve is constantly increased under the increasing load and the vacuum is therefore continuously reduced. Venting proceeds via black plastic line (arrow) leading into passenger compartment.
Damper (vacuum, 72) model year 1981 only
To reduce the high vacuum peaks, a damper is installed into vacuum line from vacuum control valve to central plug (valve plate).