Distributor: Testing and Inspection

Distributor Assembly:

ON-VEHICLE SPARK TEST

1. Disconnect coil lead from distributor cap.
2. With insulated pliers, hold wire approximately 0.20 - 0.39 in (5 - 10 mm).
3. Crank engine and verify that a strong blue spark is visible.

SPARK ADVANCE CONTROL TEST

Spark Advance Degree Chart:

Centrifugal

1. Warm engine to operating temperature.
2. Check that idle speed and timing are correct. Adjust if necessary.
3. Disconnect hose from distributor vacuum unit and plug.
4. While gradually increasing engine speed, check timing mark advance on the crank pulley.
a. Excessive advance indicates a weak governor spring. If a spring is broken, advance will be extremely high.
b. Insufficient advance indicates a malfunction such as a frozen shaft or stuck governor weight.

Vacuum

1. Warm engine to operating temperature.
2. Check that idle speed and timing are correct. Adjust if necessary.
3. Disconnect hose from distributor vacuum unit and plug.
4. Run engine at idle.
5. Attach a hand vacuum pump to distributor vacuum unit. Apply vacuum and note relationship between vacuum applied and degrees of advance. Compare to image chart.
6. If vacuum unit leaks down, it is defective and should be replaced.
7. If vacuum unit holds vacuum but advance is not as specified, check for problems such as a frozen breaker plate and repair as needed.

Positive Pressure (Boost)

1. Warm engine to operating temperature.
2. Check that idle speed and timing are correct. Adjust if necessary.
3. Disconnect hose from distributor vacuum unit and plug.
4. Connect Mazda SST #49 H080 740 or equivalent aftermarket tool to vacuum unit.
5. Gradually apply compressed air by opening tool adjustment valve. Check that timing retards as specified on image chart.