The vacuum sensor is part of the Spark Timing Control System. The sensor provides an engine load signal to the ECM. The sensor converts manifold vacuum into an electrical signal, which is transmitted to the ECM. The ECM uses this signal, along with coolant temperature and engine speed inputs, to optimize the ignition timing.
1984-88 Federal and 1987-88 California Models
See Figure 1
- Disconnect ECC 20 pin connector from control unit.
- Connect a voltmeter between ECC control unit harness terminal 9 and a known good engine ground.
- Disconnect vacuum hose for vacuum sensor and connect vacuum pump to vacuum sensor.
With no vacuum applied to the sensor, the voltmeter should read approximately 4.0 volts.
If the reading was within specifications, proceed to the next step.
Using the vacuum pump, apply 25.0 in.Hg to the sensor. The voltage measurement should be approximately 0.5 volts.
If the reading was within specifications, the sensor is okay.
REMOVAL & INSTALLATION
- Disconnect the vacuum hose from the sensor.
- Disconnect the electrical connector from the sensor.
- Remove the two bolt securing the sensor to the firewall.
- Installation is the reverse of the removal procedure.