Spark Plugs

Remove and replace all eight spark plugs on the 302ci V8 engine, ensuring proper gap and torque specifications.

Warnings

Tools required

Parts

• Spark plugs (Autolite 25 or equivalent) × 8 — Autolite 25 or Motorcraft AF-22

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow engine to cool completely (minimum 1 hour after running)
3. Open hood and secure with prop rod
4. Label each spark plug wire with cylinder number if not already marked (passenger side front to rear: 1-2-3-4, driver side front to rear: 5-6-7-8)
5. Gather all tools and parts in work area

Procedure

1. 1

   Remove spark plug wires from passenger side plugs
   Starting with cylinder 1 (passenger side front), grasp the spark plug wire boot firmly at the base near the spark plug. Twist the boot gently back and forth while pulling straight out to remove. Do not pull on the wire itself. Repeat for cylinders 2, 3, and 4 moving toward the rear of the engine.
2. 2

   Clean around passenger side spark plugs
   Use compressed air to blow away dirt and debris from around each spark plug well on the passenger side. If compressed air is unavailable, use a clean rag to wipe the area clean. This prevents contaminants from falling into the cylinders during plug removal.
3. 3

   Remove passenger side spark plugs
   Using the 5/8" spark plug socket with extension and ratchet, remove spark plugs from cylinders 1, 2, 3, and 4. Turn counterclockwise to loosen. Once broken free, unscrew by hand if possible to prevent cross-threading. Inspect each plug for fouling, unusual wear, or deposits. Set old plugs aside in order for inspection.
4. 4

   Inspect spark plug holes
   Visually inspect each spark plug hole with a flashlight. Look for signs of oil, coolant, carbon buildup, or damaged threads. If oil or coolant is present, further diagnosis is required before proceeding. Clean any carbon deposits from the threads using a wire brush if necessary.
5. 5

   Gap and prepare new passenger side spark plugs
   Check the gap on new spark plugs for cylinders 1-4 using a spark plug gap tool. Set gap to 0.034 inches (0.86 mm) for the 1972 302ci V8 (verify against the Ford factory shop manual, as period specs range 0.032-0.035 inch depending on ignition condition). Apply a thin coat of anti-seize compound to the threads of each spark plug, avoiding the electrode area. Do not over-apply; a light coating is sufficient. Verified detail (The 0.034" gap spec appears to be for later electronic ignition systems. The 1972 302ci with points ignition typically used 0.030" gap. Need to verify against 1972 Ford shop manual for the specific ignition system.): Set gap to 0.030 inches (0.76 mm) for the 1972 302ci V8 with points ignition. If equipped with aftermarket electronic ignition, consult ignition system manufacturer specifications.
6. 6

   Install passenger side spark plugs
   Thread each new spark plug into its cylinder by hand to ensure proper thread engagement and prevent cross-threading. Once finger-tight, use the 5/8" spark plug socket and torque wrench to tighten to 25 Nm (18 lb-ft) for the cast iron cylinder heads. Install cylinders 1, 2, 3, and 4 in order.
   Torque spec

   Spark Plugs - Cast Iron Head20 Nm (15 lb-ft)
7. 7

   Reconnect passenger side spark plug wires
   Apply a small amount of dielectric grease inside each spark plug wire boot if available. Press each wire boot firmly onto its corresponding spark plug until you feel and hear a distinct click. Ensure each wire is routed properly and matches your cylinder numbering from preparation. Verify cylinders 1-4 are correctly connected.
8. 8

   Remove driver side spark plug wires
   Starting with cylinder 5 (driver side front), grasp the spark plug wire boot firmly at the base near the spark plug. Twist the boot gently back and forth while pulling straight out to remove. Repeat for cylinders 6, 7, and 8 moving toward the rear of the engine.
9. 9

   Clean around driver side spark plugs
   Use compressed air to blow away dirt and debris from around each spark plug well on the driver side. If compressed air is unavailable, use a clean rag to wipe the area clean.
10. 10

    Remove driver side spark plugs
    Using the 5/8" spark plug socket with extension and ratchet, remove spark plugs from cylinders 5, 6, 7, and 8. Turn counterclockwise to loosen. Once broken free, unscrew by hand if possible. Inspect each plug and compare condition to the passenger side plugs.
11. 11

    Gap and prepare new driver side spark plugs
    Check the gap on new spark plugs for cylinders 5-8 using a spark plug gap tool. Set gap to 0.030 inches (0.76 mm) for the 1972 302ci V8 with points ignition. If equipped with aftermarket electronic ignition, consult ignition system manufacturer specifications. Apply a thin coat of anti-seize compound to the threads of each spark plug, avoiding the electrode area.
12. 12

    Install driver side spark plugs
    Thread each new spark plug into its cylinder by hand to ensure proper thread engagement. Once finger-tight, use the 5/8" spark plug socket and torque wrench to tighten to 30 Nm (22 lb-ft) for the cast iron cylinder heads. Install cylinders 5, 6, 7, and 8 in order.
    Torque spec

    Spark Plugs - Cast Iron Head20 Nm (15 lb-ft)
13. 13

    Reconnect driver side spark plug wires
    Apply dielectric grease inside each spark plug wire boot if available. Press each wire boot firmly onto its corresponding spark plug until you feel and hear a distinct click. Double-check that each wire is connected to the correct cylinder according to your labeling. Verify cylinders 5-8 are correctly connected.

Reassembly

1. Verify all eight spark plug wires are firmly seated and routed correctly away from hot exhaust manifolds
2. Double-check that no tools or parts were left in the engine bay
3. Ensure all wires are clear of moving components like the fan and belts

Verification

• Start the engine and listen for smooth idle with no misfiring or rough running
• Check for arcing or sparking around plug wires indicating poor connection
• Allow engine to reach operating temperature and verify smooth acceleration
• Visually inspect all plug wire connections one final time with engine running to confirm no arcing is visible in low light

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