EGR Valve: Testing and Inspection

The EGR System on Federal Models consists of the following components:

1. EGR (Exhaust Gas Recirculation) Valve.
2. Modulator (EGR valve modulator), or backpressure transducer.
3. VSV (Vacuum Switching Valve) controlled by the ECM.

NOTE: Before inspecting the EGR System, confirm the following:

a. On vehicles with automatic transmission, lock-up signal is not fed to the ECM at all times.
b. Manifold air temperature sensor is functioning properly.
c. See COMPUTERIZED ENGINE CONTROLS for diagnosis of the above items
d. Also refer to "CHART C-7 EGR SYSTEM CHECK" under DIAGNOSTIC CHARTS.

Comp. Loc:

INSPECTION:

Before inspection, check to make sure that gear shift lever is in neutral position (with A/T vehicle, selector lever in Park), and the parking brake lever is fully applied.

1. When engine is cool (coolant temperature is below 45°C, (113°F)) start engine and race it. Check that EGR valve diaphragm is not operating in this state by touching diaphragm with finger.

CAUTION: If EGR valve is hot, it may be necessary to wear gloves to avoid burning fingers.

Fig. 13 Checking movement of EGR valve diaphragm:

2. Warm up engine to normal operating temperature and race it after warming up. Then check to be sure that diaphragm (support) moves upward during acceleration and downward during deceleration.

Comp. Loc:

3. Keep engine running at idle speed and open the EGR valve by hand. The engine should either stop or reduce its speed. If neither occurs, the EGR passage is clogged, and must be cleaned.

If the EGR valve fails to operate properly, inspect the following:

a. EGR valve
b. EGR modulator
c. VSV
d. 5th switch for M/T vehicle
e. Lock-up signal for A/T vehicle
f. EGR valve diaphragm that it moves smoothly and that it is held at the same position when more than 20 cm Hg vacuum is applied. If diaphragm doesn't move smoothly, or it isn't held at the same position, replace the EGR valve.