The distributor in a 1997 GMC with a 5.7 is a hall-effect distributor that houses the ignition control module and the camshaft sensor. The camshaft sensor is used for control of the fuel injection system; it sends a signal to the computer concerning the position of the number 1 cylinder relative to the power stroke--it has no vacuum or mechanical advance system, since the computer handles these duties. It does, however, have a rotor for spark distribution.
Remove the air intake hose and air cleaner, using the common screwdriver. Disconnect the electrical connector on the bottom of the distributor. Mark all the spark plug wires, numbering them in a clockwise progression, starting with the number 1 cylinder wire by following the first spark plug wire closest to the radiator, on the driver's side of the vehicle back to the distributor. Work clockwise in progression for all eight wires. Another way to do this, rather than mark the wires, is to know that all the odd numbered cylinders are on the driver's side and that the even numbered ones are on the passenger's side of the vehicle. The firing order for this engine is 1-8-4-3-6-5-7-2, starting with the number 1 cylinder and working clockwise. Pull all the plug wires out of the distributor.
Remove the distributor cap by removing the screws with a Phillips screwdriver. Mark the exact location of the pointer end of the rotor relative to a point on the engine or firewall. It is vitally important to install the distributor with the rotor pointing in the exact same direction, otherwise the timing will be off. If the timing is off, a long process is necessary to locate the top dead center on the number 1 cylinder. When the distributor is installed, the pointer on the rotor should be aligned with the mark perfectly.
Remove the bolt from the distributor hold-down clamp, using a wrench. Remove the clamp. Twist the distributor back and forth as it is lifted to aid in removal.
Install a new circular gasket on the new distributor. Install the distributor by first holding it over the hole in the manifold and aligning the rotor to the approximate position necessary. Back the rotor up counterclockwise a few degrees and slide the distributor into the hole. The gear on the bottom of the distributor will cause the rotor to turn clockwise a few degrees when it engages the camshaft gear. If the rotor does not line up perfectly, lift the distributor up until the rotor is free to turn, then rotate it a few more degrees. Keep doing this process until the rotor lines up.
Install the distributor hold-down clamp and bolt and tighten it. Connect the electrical connector on the bottom of the distributor. Install the distributor cap and tighten it with the Phillips screwdriver. Install the spark plug wires as previously instructed. Install the air cleaner and air duct. Tighten them with the screwdriver.
