Running Tests

1. Connect vacuum tester with Y distributor onto EGR valve. Operate vehicle on a dynamometer (or equivalent) in 5th gear or "D" at partial load, and check vacuum reading.
a. With a vehicle speed greater than 56 ± 5 mph, 0 inches of vacuum should be obtained.
b. With a vehicle speed less than 56 ± 5 mph, 700 mbar (20 in. Hg) of vacuum should be obtained.
c. If not, check switchover valve.

2. Check electrical activation of switch-over valve.
a. Connect multimeter onto switch-over valve electrical connector and operate vehicle on a dynamometer or equivalent.
b. If voltage is obtained (approximately 12 volts) at a vehicle speed of less than 56 mph, check wiring or replace defective components.
c. If no voltage is indicated, replace switch-over valve.

3. To test the Hall effect speed sensor:
a. Disconnect the EGR control unit.
b. Measure the voltage between sockets 9 (+) and 1 (-) on the EGR control unit plug with the preglow/starter switch turned to position '2'.
c. Move the vehicle at least 1 m (3 ft).
d. Voltage should cycle between 0 and 12 vdc.
e. Repair wiring if necessary.
f. If the wiring is OK, replace the Hall effect sensor.

4. Test overvoltage protection relay.
a. Check fuse on overvoltage protection relay, and if it's bad, replace it and locate the short circuit.
b. Unplug the relay.
b. Bridge sockets 1 and 2 in the relay plug.
c. Check voltage between sockets 9 (+) and 11 (-) on the idle speed control unit plug. Battery voltage should be present. If not, check power supply wiring.
d. Turn preglow/starter switch to position '2' and check voltage between sockets 5 (-) and 6 (+) of the relay plug. Battery voltage should be present. If not, check the power supply wiring.
e. If all tests check out good, replace the overvoltage protection relay.