Throttle Body Fuel Injection System

Fig. 085 - Wiring Diagram for Chart C-7 EGR Check. VIN Z:

CHART C-7, EXHAUST GAS RECIRCULATION

The Exhaust Gas Recirculation (EGR) valve is controlled by a normally open solenoid (allows vacuum to pass when de-energized.)
When the ECM energizes the solenoid, by completing a ground circuit, the EGR is turned "OFF". The ECM controls EGR based on the following inputs:
a. Engine Coolant - about 25°C
b. Throttle Position Sensor - off idle and steady
c. Manifold Absolute Pressure - steady throttle
d. Vehicle Speed - over 5 MPH

Fig. 084 Chart C-7 EGR Check:

1. This tests for restricted valve or passage in manifold. Engine should run roughly as valve is opened manually.
2. EGR valve diaphragm should begin to move as the engine speed approaches 1000 to 1200 RPM.
3. This checks for proper vacuum at the EGR valve. It should approach normal engine vacuum but definitely be at least 10".
4. This checks vacuum to the EGR solenoid at the manifold. It should be manifold vacuum.
5. Grounding the "test" terminal of the ALCL connector removes power to the EGR circuit (435). The light should be off.
6. Solenoids are turned "ON" or "OFF" by the ECM internal electronic switches called "drivers". Each driver is part of a group of four called "Quad-Drivers". Failure of one can damage any other driver within the set.
Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause early failure of the ECM "DRIVER". Using an ohmmeter, check the solenoid coil resistance of all ECM controlled solenoids and relays before installing a replacement ECM.