GM Lumina/Silhouette/Transport APVs 1990-1999 Repair Guide

Distributor Cap and Rotor


Ignition systems have changed dramatically since these vehicles were first introduced. Most vehicles today use coil packs instead of distributors. They have no need of distributor caps or rotors. Camshaft and crankshaft sensors have replaced these items. For the most part, timing is no longer adjustable, but is being controlled by the PCM (Powertrain Control Model). However, in the interest of those vehicles that operate with a distributor cap and rotor, some basic information will be given.


A physical inspection of the distributor cap and rotor should be done at the same time as the plug wires are being checked. When inspecting the distributor cap, check for obvious signs of damage, such as a broken tower, crack in the body of the cap, or external carbon tracks . When checking on the inside of the cap, use a bright light to illuminate the inner surface. Check for charred or eroded terminals, inspect for carbon tracks that go from terminal to terminal or run to the bottom of the cap. Look for a worn or damaged rotor button (center electrode). Also take a close look at the inside terminals for metal to metal contact. Damaged or cut terminals could mean a rotor or cap that was not properly installed; or it could mean that the distributor housing has worn beyond its limits and the shaft is wobbling when it rotates, or that the distributor shaft is bent.


  1. Remove the secondary wiring (spark plug wires) if a new cap is being installed

See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: Exploded view of the distributor used on 3.1L engines

Record wire placement at each wire location in order to maintain the correct firing order.

  1. Simultaneously depress and rotate the two retaining screws counterclockwise, in the cap, 180° to disengage from the distributor housing.
  3. Remove the cap, this exposes the ignition rotor.
  5. Remove the two hold down screws retaining the rotor to the distributor shaft. Note the position of the rotor.

To install:
  1. To install the rotor, align it to the distributor shaft. Do not put the square peg into the round hole!

The rotor can be mounted incorrectly. If this occurs the engine timing will be off by 180°. Be careful to align the rotor properly, it should seat snugly and level on the distributor shaft.

  1. Seat the distributor cap onto the distributor housing, making sure to align the cap properly.
  3. Simultaneously depress and rotate the cap screws clockwise 180° to hold the cap in place.