Starting with 1974 models, exhaust gas recirculation (EGR) was used on 18R-C, and 4M engines sold in California. All engines, since 1975 use EGR.
In all cases, the EGR valve is controlled by the same computer and vacuum switching valve which is used to operate other emission control system components.
On four cylinder engines, the EGR valve is operated by vacuum supplied from a port above the throttle blades and fed through the vacuum switching valve.
On M engines, vacuum from the carburetor vacuum advance port flows through the vacuum switching valve to an EGR vacuum control valve. The vacuum from the advance port opens the vacuum control valve which then allows venturi vacuum to act on the chamber above the EGR valve diaphragm, causing the EGR valve to open. When exhaust gas recirculation is not required, the vacuum switching valve stops sending the advance port vacuum signal to the EGR vacuum control valve which closes, sending intake manifold vacuum to the chamber below the EGR valve diaphragm. This closes the EGR valve, blocking the flow of exhaust gases to the intake manifold.
On all engines there are several conditions, determined by the computer and vacuum switching valve, which permit exhaust gas recirculation to take place:
- Vehicle speed.
- Engine coolant temperature.
- EGR valve temperature (4 cylinder).
- Carburetor flange temperature (4 cylinder).
On 4-cylinder engines equipped with EGR, the exhaust gases are carried from the exhaust manifold to the EGR valve and from the EGR valve to the carburetor, via external tubing. Some later engines have an exhaust gas cooler mounted on the back of the cylinder head.
On M series engines, the EGR valve is mounted on the exhaust manifold and exhaust gases from it are carried through external tubing to the intake manifold.
18R-C, 20R AND 22R ENGINES
- Allow the engine to warm up and remove the top from the air cleaner.
Do not remove the entire air cleaner assembly.
- Disconnect the hose (white tape coded), which runs from the vacuum switching valve to the EGR valve, at its EGR valve end.
- Remove the intake manifold hose (red coded) from the vacuum switching valve and connect it to the EGR valve. When the engine is at idle, a hollow sound should be heard coming from the air cleaner.
- Disconnect the hose from the EGR valve. The hollow sound should disappear.
- If the sound doesn't vary, the EGR valve is defective and must be replaced.
- Reconnect the vacuum hoses as they were originally found. Install the top on the air cleaner.
- Warm up the engine and allow it to idle.
- Disconnect the vacuum sensing line from the upper vacuum chamber of the EGR valve.
- Disconnect the sensing line from the lower chamber of the EGR valve.
- Now, take the hose which was disconnected from the lower chamber and connect it to the upper EGR valve chamber.
Leave the lower chamber vented to the atmosphere.
- The engine idle should become rough or the engine should stall with the hoses connected in this manner. If the engine runs normally, check the EGR vacuum control valve (see below). If the vacuum control valve is in good working order, then replace the EGR valve.
- Reconnect the vacuum sensing lines as they were originally found.
18R-C, 20R AND 22R ENGINES
- Disconnect the electrical lead which runs to the EGR valve thermo-sensor.
- Remove the thermo-sensor from the side of the EGR valve.
- Heat the thermo-sensor in a pan of water to 260°F.
- Connect an ohmmeter, in series with a 10 ohm resistor, between the thermo-sensor terminal and case.
- With the ohmmeter set on the K omega scale, the reading should be 2.55 K omega .
- Replace the thermo-sensor if the ohmmeter readings vary considerably from those specified.
- To install the thermo-sensor on the EGR valve, tighten it to 15-21 ft. lbs.
EGR Vacuum Control Valve
M SERIES ENGINES
- Connect the EGR vacuum control valve hoses up, so that carburetor advance port vacuum operates directly on its diaphragm (top hose connection).
- Disconnect the two hoses from the EGR vacuum control valve which run to the upper and lower diaphragm chambers of the EGR valve.
- Take two vacuum gauges and connect one to each of the ports from which you removed a hose in Step 2.
- Race the engine. The vacuum gauges should indicate the following:
Upper chamber port-Venturi vacuum
Lower chamber port-Atmospheric pressure
- Disconnect the sensing hose from the carburetor advance port.
- The vacuum gauges should now show the following:
Upper chamber port-Atmospheric pressure
Lower chamber port-Intake manifold vacuum.
The atmospheric pressure reading should be nearly equal to that obtained in Step 4.
- Replace the EGR vacuum control valve if the readings on the vacuum gauges are incorrect.
- Hook up the vacuum lines as they were originally found.
If, after having completed the above tests, the EGR system still doesn't work right and everything else checks out OK, the fault probably lies in the computer or the vacuum switching valve systems. If this is the case, it is best to have the car checked out by test facility which has the necessary Toyota emission system test equipment.
A good indication that the fault doesn't lie in the EGR system, but rather in the vacuum supply system, would be if several emission control systems were not working properly.