The 4.5-liter engine on a 1990 Cadillac Coupe DeVille has many different moving components, and all of them have to work together in harmony or else the engine won't run. The process which helps everything to work correctly is called the ignition timing, and it needs to be very precise. If not, the engine will run poorly, if at all. When you need to adjust your timing, you can do so in less than an hour with a few tools.
Park the Cadillac and put on the parking brake. Open the hood and locate the number one spark plug wire, which is the furthest forward on the drivers side on the engine. Attach the clamp from the timing light to the number one spark plug wire.
Start the engine. Locate the timing marks on the engine, which are both on the crankshaft pulley and on a bracket next to the pulley. Shine the timing light where the mark on the pulley intersects with the mark on the bracket. Look at the number on the bracket at that intersection, and note the current timing. Turn off the engine.
Cut the 10-gauge wire to approximately four inches. Strip 1/2-inch off both ends of the wire using the wire strippers. Open the driver door and locate the ALDL connector, which is the plug underneath the steering column used for diagnosis. Insert one end of the wire into the top right port on the plug, and the other end into the port just to the left of the top right port.
Start the engine. Loosen the distributor hold-down clamp with an open-end wrench. Shine the timing light onto the pulley and turn the distributor slowly until the timing is adjusted to the amount you want. Tighten the distributor hold down clamp with an open-end wrench and remove the wire from the ALDL connector.
