EGR System - Gasoline Nissan 300ZX Z31

DESCRIPTION

The Exhaust Gas Recirculation (EGR) system recirculates exhaust gases into the combustion chamber to reduce combustion temperatures. The reduction in temperature acts to reduce oxides of nitrogen (NOx) emissions. On all models except Maxima, 300ZX and 300ZX Turbo, the system consists of an EGR control valve, thermal vacuum valve (TVV) (except on Fed. Pulsar and Sentra), backpressure transducer valve (BPTV) (except on Calif. Pulsar and Sentra), and various connecting hoses and tubes.

On Maxima, 300ZX and 300ZX Turbo, the EGR system is controlled by the ECCS control unit. The system consists of EGR Control Valve, EGR Control Solenoid Valve, Throttle Valve Switch, Cylinder Head Temperature Switch and Crank Angle Switch.

EGR System (1986 Pickup & 1986 1/2 Pickup - Z24i Engine). Scheme 8

MAXIMA, 300ZX & 300ZX TURBO

When the EGR valve is held open, some of the exhaust gas is led from the exhaust manifold to the EGR tube. The exhaust gas is then regulated by the EGR valve, and introduced into the intake manifold. The signal from the ECCS control unit is sent to the EGR control solenoid valve, which cuts the vacuum line for the EGR control valve when engine is starting, throttle valve switch is on, engine coolant temperature is low, or engine speed is below 900 RPM or above 3200 RPM.

EXCEPT MAXIMA AND 300ZX MODELS

Exhaust gases are directed from the exhaust manifold, through EGR tube and into EGR control valves. The BPT valve monitors exhaust pressure in order to control intake manifold vacuum applied to EGR control valve. The EGR control valve regulates actual amount of exhaust gas to be recirculated into intake manifold.

Open/Close operation of EGR control valve is directed by the thermal vacuum valve which operates on ported vacuum and engine coolant temperature. EGR system does not operate at idle or under full throttle (heavy load) conditions, when coolant temperature is low (thermal vacuum valve closed), or when exhaust pressure is low.

EGR System (Pulsar & Sentra). Scheme 9

EGR System (Stanza). Scheme 10

THERMAL VACUUM VALVE

1. Drain engine coolant. Remove thermal vacuum valve from engine leaving hoses attached. Without letting water enter valve, submerge valve and thermometer in a container of water.
2. Heat water and observe temperature. Apply vacuum to EGR port. Check that valve opens and closes according to specified value. If valve does not operate as specified, replace valve.

Thermal Vacuum Valve (TVV). Scheme 11

EGR VALVE

1. Remove EGR valve from engine and inspect it for damage. Apply vacuum to EGR valve and watch diaphragm movement.
2. Diaphragm should move to fully open position and should remain in this position for at least 30 seconds after vacuum is shut off.
3. Before reinstalling EGR valve, clean mating surface with a wire brush and compressed air. Remove foreign material from around valve and port.

Typical EGR Valve. Scheme 12

BACKPRESSURE TRANSDUCER (BPT) VALVE

Disconnect 2 vacuum hoses on BPT valve. Plug one of 2 ports. Apply pressure of .145 in. Hg. to BPT valve and apply suction on other port to check for leakage. If leak is noticed, replace valve.

Backpressure Transducer (BPT) Valve. Scheme 13

Note. The EGR system on Maxima, 300ZX models and 1986 1/2 Pickup is controlled by the Electronic Concentrated Engine Control System (ECCS) control unit. See ELECTRONIC CONCENTRATED ENGINE CONTROL SYSTEM article for testing.

Scheme 14

1. 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. (Scheme 14): EGR System (200SX)
2. With engine running, check operation of EGR valve and thermal vacuum valve by placing finger on diaphragm of EGR valve and checking diaphragm movement.
3. With engine coolant temperature below "Closed" value, increase engine speed to 3000-3500 RPM (2000-2500 RPM on Pickup). EGR valve diaphragm should remain closed.
4. With engine coolant temperature above "Open" value, increase engine speed to 3000-3500 RPM (2000-2500 RPM on Pickup). EGR valve diaphragm should open and allow exhaust gas recirculation.
5. 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 (2000-2500 RPM on Pickup). Check for vacuum at end of disconnected hose.
6. If vacuum is present, check EGR or BPT valves. If no vacuum is present, check TVV valve. If vacuum is weak or not present, replace TVV.

EGR System (Maxima, 300ZX Models And 1986 1/2 Pickup - VG30i Engine). Scheme 15

THERMAL VACUUM VALVE SPECIFICATIONS (1)