1979 Models

With engine stopped, visually inspect entire EGR system and clean as necessary. Replace hoses that are cracked or broken. Inspect EGR valve for signs of binding or sticking by moving valve diaphragm upwards with finger.
With engine running, check operation of EGR valve and thermal vacuum valve by placing finger on diaphragm of EGR valve and checking diaphragm movement.
With engine coolant temperature below closed value shown in EGR SYSTEM TEST SPECIFICATIONS table, increase engine speed to 3000-3500 RPM. The EGR valve should remain closed.
With engine coolant temperature above open value shown in EGR SYSTEM TEST SPECIFICATIONS table, increase engine speed to 3000-3500 RPM. The EGR valve should open and allow exhaust gas recirculation.
If EGR valve does not operate as indicated, disconnect EGR valve-to-thermal vacuum valve vacuum hose at EGR valve. Increase engine speed to 3000-3500 RPM and check for vacuum at end of disconnected hose.
If vacuum is present, replace EGR valve. If vacuum is weak or not present at all, replace thermal vacuum valve.

EGR SYSTEM TEST SPECIFICATIONS

Application

Valve Closed
°F (°C)

Valve Open
°F (°C)

210 & 310

122 (50)

145 (63)

280ZX & 810

⁽¹⁾

⁽²⁾

All Others

104 (40)

127 (53)

⁽¹⁾	Below 117°F (47°C) and above 208°F (98°C).

⁽²⁾	Between 122°F (50°C) and 203°F (95°C).

Fig 1: 1978-79 280ZX & 810 EGR System

Courtesy of NISSAN NORTH AMERICA, INC.

Fig 2: 1978-79 200SX, 510 & Pickup EGR System

Courtesy of NISSAN NORTH AMERICA, INC.