If you touched the distributor while changing the cap (e.g., bumped it, rotated it), then you'll need to set the ignition timing. This is more involved:
If you DID disturb the distributor:
1. Safety First: Disconnect the negative battery cable before working on the ignition system.
2. Find Top Dead Center (TDC) on #1 Cylinder: This is crucial. With the distributor rotor pointing at the #1 cylinder terminal on the cap, the #1 piston should be at TDC on the compression stroke. You'll need to use a timing light and possibly a compression gauge, or a degree wheel for precise setting, to be absolutely certain the piston is at TDC and the rotor is pointing to the #1 terminal. The easiest way to find TDC is to use a piston stop tool through the spark plug hole.
3. Loosen Distributor Clamp: Carefully loosen the distributor hold-down clamp just enough to allow slight rotation of the distributor.
4. Initial Timing Setting: Consult your owner's manual or a reliable 454 engine repair manual for the correct initial timing specification for your engine. This is usually expressed in degrees before top dead center (BTDC). You'll typically find this on a sticker under the hood, but the manual is preferable if present.
5. Use a Timing Light: Connect the timing light to the #1 spark plug wire and the battery. With the engine running, aim the timing light at the timing tab on the harmonic balancer (the pulley at the front of the crankshaft). The light will illuminate the timing marks.
6. Adjust Distributor: While watching the timing marks through the timing light, carefully rotate the distributor slightly. You'll adjust the distributor to match the specified BTDC initial timing. Tighten the distributor clamp once you have the correct timing.
7. Recheck Timing: After tightening, double-check your timing. Small adjustments might be necessary.
8. Reconnect Battery: Reconnect the negative battery cable.
Important Considerations:
* Engine Type: The exact procedures and timing specs will vary slightly depending on the specific 454 engine you have (e.g., different camshafts, etc.). Your owner's manual (if you have it) is the most authoritative source. A reputable repair manual is also highly recommended.
* Vacuum Advance: After setting the initial timing, you'll usually need to check and adjust the vacuum advance. Consult your repair manual for the procedure.
* Mechanical Advance: Some distributors have mechanical advance weights that cannot be easily adjusted. If the initial timing is very far off, it could indicate a mechanical advance problem.
If you're not comfortable working with ignition systems or aren't mechanically inclined, taking your vehicle to a qualified mechanic is the safest and best option. Incorrect timing can damage your engine.
