Ignition Timing

NOTE: Engines are equipped with a receptacle for magnetic probe timing lights, located 10° ATDC. Do not use this location for timing with a conventional light.

Fig 1: Firing Order and Timing Marks (All Engines)

Courtesy of GENERAL MOTORS COMPANY

Connect an adapter between No. 1 spark plug and No. 1 spark plug wire or use an inductive type pickup. Do not puncture wires.
Connect timing light according to manufacturer's instructions. Check or adjust ignition timing with engine at normal operating temperature, distributor vacuum line disconnected and plugged. Place transmission in neutral, except for Light Duty models with automatic which should be in "D". Set timing to specifications.
To adjust timing, loosen distributor hold down bolt and rotate distributor until timing is to specifications. Tighten hold down bolt.

Ignition Timing Specifications (Degrees BTDC@RPM)

Application

Man. Trans.

Auto. Trans.

Light Duty

5.0L 2-Bbl.

8@700

8@600

5.0L 4-Bbl.

Federal

⁽¹⁾ 4@700

⁽²⁾ 8@650

Calif.

.....

8@650

5.7L 4-Bbl.

Federal

8@700

8@600

Calif.

.....

⁽³⁾ 6@650

Heavy Duty

5.7L 4-Bbl.

Federal

4@700

Calif.

6@700

7.4L 4-Bbl.

4@700

⁽¹⁾	Set Van to 6° BTDC.

⁽²⁾	Set Decal AAN to 6° BTDC; Decal AAS to 2° BTDC.

⁽³⁾	Set Van to 8° BTDC.