Most engines, except for early 2T-C engines, use EGR system. 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 all engines there are several conditions, determined by the computer which permit exhaust gas recirculation to take place:
- Vehicle speed.
- Engine coolant temperature.
- EGR valve temperature.
- Carburetor flange temperature.
EGR VALVE CHECK
See Figure 1
- Allow the engine to warm up and remove the top from the air cleaner.
- 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.
See Figure 2
- Start the engine.
- Disconnect the vacuum hose leading from the EGR valve.
- Disconnect the hose coming from the intake manifold and connect it to the empty pipe on the EGR valve.
- When applying vacuum directly to the EGR valve, the engine should stall, if not, the EGR valve will probably require replacement.
EGR VALVE THERMOSENSOR
- Disconnect the electrical lead which runs to the EGR valve thermosensor.
- Remove the thermosensor from the side of the EGR valve.
- Heat the thermosensor in a pan of water to the following temperature: 260°F.
- Connect an ohmmeter, in series with a 10 ohms resistor, between the thermosensor terminal and case.
- With the ohmmeter the following reading should be obtained: 2.55 kilo ohms.
- Replace the thermosensor if the ohmmeter readings vary considerably from those specified.
- To install the thermosensor on the EGR valve, tighten it to 15-21 ft. lbs. (20-28 Nm)
CHECKING THE EGR VACUUM MODULATOR
See Figure 3
- Tag and disconnect all hoses leading from the vacuum modulator.
- Remove the vacuum modulator.
- Unscrew the vented top plate and remove the filter.
- Check the filter for any contamination or other damage.
- Clean the filter using compressed air.
- Installation is in the reverse order of removal.
If, after having completed the above tests, the EGR system still doesn't work right and everything else checks out OK, the fault may probably lie in the computer. If this is the case, it is best to have the car checked out by a test facility which has the necessary Toyota emission system test equipment.
REMOVAL & INSTALLATION
See Figures 4, 5, 6 and 7
Exhaust emission control equipment is generally simple to work on and easy to get to on the engine. The air cleaner assembly will need to be removed. Always label each vacuum hose before removing it-they must be replaced in the correct position.
Most of the valves and solenoids are made of plastic, particularly at the vacuum ports. Be very careful during removal not to break or crack the ports; you have NO chance of regluing a broken fitting. Remember that the plastic has been in a hostile environment (heat and vibration); the fittings become brittle and less resistant to abuse or accidental impact.
The EGR valve is held in place by mounting bolts. The bolts can be difficult to remove due to corrosion. Remove the air cleaner assembly and all necessary components for access to the EGR valve mounting bolts. Once the EGR is off the engine, clean the bolts and the bolt holes of any rust or debris. Always replace the gasket any time the EGR valve is removed.