Computers and Control Systems: Testing and Inspection

Prior to testing:
1. Disconnect vacuum line between vacuum control valve (VCV) for evaporative emission control (EVAP) and vacuum connector at connector end. Plug vacuum connector.

2. On vehicles equipped with high altitude compensation systems (HAC), disconnect the vacuum line between the HAC valve and the check valve, at the check valve end.

Testing
1. Disconnect the vacuum line between the vacuum switching valve (VSV) and carburetor at VSV end, and plug hose.

2. Disconnect vacuum line between VSV and vacuum pipe at pipe end. Using a fitting, and a suitable length of additional hose, connect VSV to intake manifold with vacuum gauge installed between these two points. Place vacuum gauge so that it can be read while road testing vehicle.

3. Start engine and bring to normal operating temperature. Road test vehicle while observing vacuum gauge reading and speedometer. High vacuum should be indicated at speeds below 33 mph. Vacuum reading should fluctuate between low and high vacuum at speeds above 42 mph.

4. If proper readings are obtained, system is good. If not, check speed sensor, vacuum switching valve (refer to evaporative emissions section), and oxygen sensor (refer to air suction system).