GM Full Size Vans 1967-1986 Repair Guide



Neither tune-up nor troubleshooting can be considered independently since each has a direct relationship with the other.

It is advisable to follow a definite and thorough tune-up procedure. Tune-up consists of three separate steps: Analysis, the process of determining whether normal wear is responsible for performance loss, and whether parts require replacement or service; parts replacement or service; and adjustment, where engine adjustments are performed.

The manufacturer's recommended interval for tune-ups is every 12,000 miles (19,000 km) or 12 months, whichever comes first for 1970-74, and 22,500 miles (36,200 km) or 18 months for 1975-86, except for heavy duty emission models, which use the 12 month/12,000 miles (19,000 km) schedule in all years. These intervals should be shortened if the truck is subjected to severe operating conditions such as trailer pulling, or if starting and running problems are noticed. It is assumed that the routine maintenance described in General Information & Maintenance has been kept up, as this will have an effect on the results of the tune-up. All the applicable tune-up steps should be followed, as each adjustment complements the effects of the others. If the tune-up (emission control) sticker in the engine compartment disagrees with the information presented in the Tune-up Specifications chart in this section, the sticker figures must be followed. The sticker information reflects running changes made by the manufacturer during production. The light duty sticker is usually found on the underhood sheet metal above the grille. The heavy duty sticker is usually on top of the air cleaner.

Diesel engines do not require tune-ups per say, as there is no ignition system.

Troubleshooting is a logical sequence of procedures designed to locate a particular cause of trouble. It is advisable to read the entire section before beginning a tune-up, although those who are more familiar with tune-up procedures may wish to go directly to the instructions.