Cold/Hot Engine Test

Cold Engine

1. Ensure engine is cold, disconnect vacuum hose from EGR valve and connect suitable gauge to hose.
2. Start engine and run at approximately 3000 RPM.
3. If vacuum is indicated on gauge, replace thermovalve and recheck operation. If no vacuum is indicated, proceed to hot engine test.



Hot Engine

1. Disconnect vacuum hose from EGR valve and connect suitable gauge to hose.
2. Start engine and run until it reaches normal operating temperature.
3. Remove control box from firewall and remove cover from control box.
4. Observe vacuum reading with engine running at idle. No vacuum should be indicated.
5. If vacuum is indicated at idle, check vacuum hose routing, idle speed and mixture adjustment and correct as needed.
6. Note vacuum reading with engine running at 4500 RPM for 1985 models or 3000 RPM for 1986-87 models and while accelerating engine. Gauge should indicate 2-6 inches Hg vacuum. If no vacuum is indicated, proceed as follows:
a. Check for vacuum at inlet and outlet of thermovalve.
b. If vacuum is present at inlet of valve, but not at outlet, replace thermovalve.
c. If no vacuum is available to thermovalve, check routing of vacuum hoses and repair as needed.
7. Disconnect control valve bleed hose from air filter, plug hose, then note vacuum reading with engine running at 4500 RPM for 1985 models or 3000 RPM for 1986-87 models. If reading is greater than 2 inches Hg, replace control valve and ensure vacuum hoses are properly routed.
8. Road test vehicle and observe vacuum reading to EGR valve during deceleration. If vacuum is available during deceleration, control valve is defective.