In order to extract the full measure of performance and economy from your engine it is essential that it is properly tuned at regular intervals. A regular tune-up will keep your truck's engine running smoothly and will prevent the annoying breakdowns and poor performance associated with an untuned engine.
All gasoline models covered in this manual are equipped with an electronic distributor ignition system known as High Energy Ignition (HEI) or more recently as Distributor Ignition (DI).
A complete tune-up should be performed at least every 30,000 miles. This interval should be halved if the truck is operated under severe conditions such as trailer towing, prolonged idling, start-and-stop driving, or if a driveability problem such as hard starting or poor running is noticed. It is assumed that the routine maintenance described in Chapter 1 has been kept up, as this will have a decided effect on the results of a tune-up. All of the applicable steps of a tune-up should be followed in order, as the result is a cumulative one. Any adjustment made to the engine is normally performed only when it will not be affected by other adjustments that are yet to be made during the tune-up.
Diesel engines do not require tune-ups per se, as they do not have spark plug ignition systems.
If the specifications on the underhood tune-up sticker (located in the engine compartment of your truck) disagree with the tune-up specifications chart in this Section, the figures on the sticker must be used. The sticker often reflects changes made during the production run or revised information that apply to the particular systems in that vehicle.