GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC C-Series Medium Duty Truck B7 🢒 Engine 🢒 Engine Controls - 7.4L 🢒 Spark Plug Replacement

Removal Procedure
  1. Remove the spark plug wires. Refer to Spark Plug Wire Harness Replacement .

    2. Object Number: 172979 Size: SH
  2. Loosen each spark plug one or two turns.

    3. Most spark plug are best removed from wheel wells.

  3. Brush or air blast away any dirt from around the spark plugs.
  4. Remove the spark plugs one at a time and place each plug in a tray marked with the corresponding cylinder numbers.

Installation Procedure

    Object Number: 172979 Size: SH
  1. Properly position each spark plug washer.
  2. Inspect each spark plug gap. Adjust each plug as needed.

    3. Specification
    Spark plug gap: 1.524 mm (0.060 in)

    Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

  3. Install the spark plugs.

    4. Tighten 7.4L

        • For (IRON Head-all Subsequent Installations) tighten the spark plugs to 20 N·m (15 lb ft) for 7.4L.
        • For new iron heads tighten the spark plugs to 30 N·m (22 lb ft) for 7.4L.
  4. Install the spark plug wires. Refer to Spark Plug Wire Harness Replacement .