System Diagnosis

Cold Engine

Coolant temperature must be below 145.4°F.

1. Disconnect No. 16 vacuum hose from EGR valve and connect vacuum pump to hose.
2. Start engine and raise engine speed to 3000 RPM. There should be no vacuum.
3. If there is no vacuum, perform ``Hot Engine'' test.
4. If there is vacuum, test components of evaporative emission control system.

Hot Engine

1. Disconnect No. 16 vacuum hose from EGR valve and connect vacuum pump to hose.
2. Start engine and warm to normal operating temperature, then check vacuum. Vacuum should be as follows:
a. At idle, there should be no vacuum.
b. At 3000 RPM, there should be 2-6 inches Hg vacuum.
c. At 3000 RPM with blocked vacuum bleed, there should be vacuum of less than 2 inches Hg.
d. At rapid deceleration, there should be 2-6 inches Hg vacuum.
e. At deceleration, there should be no vacuum.
3. Remove control box and open control box lid.
4. If there is vacuum in step a, check vacuum hoses for proper routing and connections, then check idle speed and mixture, adjusting as necessary.
5. If there is no vacuum in steps b and d, test components of evaporative emission control system.
6. If vacuum is greater than 2 inches Hg in step c, replace EGR control valve and check vacuum hoses for proper routing and connections.