Spark Control System (Spk)

Fig. 117 Checking Vacuum To The Vacuum Advance Diaphragm:

1. Disconnect the vacuum hoses, (#2 and #25), from the vacuum advance diaphragm, Fig. 117.
2. With the engine at idle, and the coolant temperature below 60°C (140°F), check for vacuum at each of the hoses. Vacuum should be available at both hoses.
a. If no vacuum is available at hose #2 (connected directly to manifold vacuum), check hose for proper connection, cracks or blockage.
b. If no vacuum is available at hose #25, check the #24 and #25 hoses for proper connections, cracks, or blockages, and make sure that the check valve operates properly. If the hoses and check valve are OK, replace the thermovalve and re-test.
3. Connect the vacuum lines back to the advance diaphragm and allow the engine to warm up (the cooling fan should cycle ON and OFF at least once).
4. Disconnect the #25 vacuum hose from the vacuum advance unit and check for vacuum. No vacuum should be available. If vacuum is available, replace the thermovalve and re-test.
5. Disconnect the vacuum hoses from the vacuum advance diaphragm and plug them.

Fig. 118 Timing Light Hookup:

6. Connect a timing light and an advance tester, and remove the rubber cap from the inspection window of the cylinder block, Fig. 118.
7. With the engine at idle, point the timing light at the timing mark, (on the flywheel for manual transmissions, or the drive plate for automatic transmissions).

Fig. 119 Ignition Timing Marks:

8. Align the timing mark (white) to the pointer by turning the advance control knob of the advance tester, Fig. 119.
9. Read the basic timing when the white timing mark is aligned with the pointer. Ignition timing should be:

Manual Trans. @ 800 +/- 50 rpm 4°BTDC
Automatic Trans. @ 750 +/- 50 rpm (in neutral) 4°BTDC

10. Adjust timing as necessary by loosening the hold down bolts and turning the distributor.
11. Connect the vacuum hoses to the vacuum advance diaphragm, and check the timing.

Manual Transmission @ 800 +/- 50 rpm
49 State 20° +/- 2°BTDC (red mark)
California 15° +/- 2°BTDC (red mark)
Automatic Transmission @ 750 +/- 50 rpm (in neutral)
49 State 15° +/- 2°BTDC
California 10° +/- 2°BTDC

12. If the ignition timing is not within specifications with the vacuum advance connected, test the vacuum advance diaphragm.