Hot Engine

Ensure engine is at normal operating temperature. Disconnect vacuum hose No. 8 at vacuum advance diaphragm B. Connect a vacuum gauge to hose.
Start engine and check for vacuum at idle. If no vacuum is present, proceed to step 6). If vacuum is present, check for voltage at vacuum control solenoid valve in emission control box 4P connector Blue/Black wire.
If there is voltage, check the following: On man. trans. models, check thermosensor and intake air temperature sensor. Check for voltage at control box connector (Black/Yellow wire) with ignition on. There should be voltage. If no voltage, check wiring. Ensure Brown/Black wire between control unit and ground has continuity.
On auto. trans. models, check for voltage at control unit connector (Blue wire) with ignition on. There should be voltage. If no voltage, check Blue wire between control unit and ignition coil. Check speed sensor, thermosensor, intake air temperature sensor and vacuum switch C.
Check for voltage at control box connector (Black/Yellow wire) with ignition on. There should be voltage. If no voltage, check wiring. Ensure Brown/Black wire between control unit and ground has continuity. If there is no voltage, replace vacuum control solenoid valve and retest.
Disconnect both vacuum hoses from the distributor advance unit. Plug both disconnected hoses. Using a "T" fitting and vacuum hose, connect a vacuum pump to both diaphragms.
Pinch vacuum hose to diaphragm B. Apply 16 in. Hg to diaphragm A. If ignition timing advances and holds steady, proceed to step 8). If timing will not advance or does not hold vacuum, check distributor breaker plate for binding condition. If no trouble is found, replace vacuum advance unit.
Release pinched vacuum hose and apply 16 in. Hg to both diaphragms. If ignition timing advances more than step 7) and holds steady, system is okay. If ignition timing does not advance as described, replace vacuum advance unit and retest.