Spark Plug Wires

Replace the spark plug wires on the 390ci V8 engine to restore proper ignition system performance and eliminate misfires.

Warnings

Tools required

Parts

• Spark plug wire set (8 cylinder) × 1 — Use OEM specification or performance equivalent rated for 390ci V8

Preparation

1. Ensure engine is cool to the touch
2. Park vehicle on level surface and engage parking brake
3. Open hood and secure with prop rod
4. Verify you have the correct wire set for the AMC 390ci V8 with appropriate length wires

Procedure

1. 1

   Document existing wire routing
   Before removing any wires, note the routing path of the existing wires, paying special attention to how they pass around the valve covers, over the intake manifold, and through any wire looms or separators. Take photos if possible. The AMC 390 uses a specific routing pattern to avoid contact with hot exhaust components.
2. 2

   Label wires for reference
   Using masking tape and marker, label each wire with its cylinder number (1-8) before removal. Cylinder 1 is the front cylinder on the passenger side. Passenger side runs 1-3-5-7 front to rear, driver side runs 2-4-6-8 front to rear. This prevents installation errors.
3. 3

   Remove distributor cap
   Locate the distributor on the driver side of the engine. Remove the distributor cap retaining clips or screws (depending on cap type) and carefully lift the cap with wires still attached. Set it aside in a position where the wires are not strained.
4. 4

   Replace wires one at a time
   Starting with cylinder #1, grasp the spark plug wire boot firmly at the spark plug end and twist gently while pulling straight out. Do not pull on the wire itself. Remove the same wire from the distributor cap by pulling the boot straight out. Immediately install the corresponding new wire from the spark plug to the distributor cap position, ensuring it follows the same routing path.
5. 5

   Apply dielectric grease
   Before installing each new wire, apply a small amount of dielectric grease inside both the spark plug boot and distributor cap terminal boot. This prevents moisture intrusion and makes future removal easier.
6. 6

   Install new wire to spark plug
   Push the new wire boot firmly onto the spark plug terminal until you feel and hear a definite click or snap, indicating the boot has fully seated on the plug terminal. The boot should be snug and not easily pulled off.
7. 7

   Install wire to distributor cap
   Route the wire following the original path documented earlier, then push the distributor end boot firmly into the corresponding distributor cap tower until fully seated. Ensure the wire is properly secured in any wire looms or separators.
8. 8

   Continue with remaining cylinders
   Repeat steps 4-7 for each remaining cylinder, replacing only one wire at a time. Follow the firing order sequence (1-8-4-3-6-5-7-2) to maintain organization. Double-check that each wire goes to the correct cylinder and distributor cap position.
9. 9

   Secure wires in looms
   Once all wires are installed, ensure they are properly seated in the factory wire looms or separators. Wires should be routed away from exhaust manifolds, sharp edges, and moving components. Maintain proper separation between wires to prevent cross-firing.
10. 10

    Reinstall distributor cap
    Position the distributor cap back onto the distributor body, ensuring it is properly aligned. Secure with the retaining clips or screws. Verify the cap is firmly seated and all wires are clear of interference.
11. 11

    Inspect wire routing
    Perform a final inspection of all wire routing. Check that no wires contact the exhaust manifolds, valve covers, or other hot components. Verify wires are clear of the throttle linkage and have adequate clearance from the fan and fan shroud.

Reassembly

1. Verify all eight spark plug wires are firmly seated at both the spark plug and distributor cap ends
2. Confirm all wire looms and separators are properly positioned
3. Double-check that wires follow the correct firing order and are routed away from heat sources

Verification

• Start the engine and listen for smooth idle with no misfiring or hesitation
• Rev the engine slowly and verify no arcing or spark jumping between wires (check in darkness if possible)
• Verify engine runs smoothly under acceleration with no stumbling or misfiring
• Check that all wires remain properly secured and do not contact moving or hot components during engine operation

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