GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC K Pickup - 4WD (CNG) 🢒 Engine 🢒 Engine Controls - 5.0L and 5.7L 🢒 Fuel Tank Inspection
    • Inspect the CNG fuel tank and brackets every 3 years or 36,000 miles (60 000 km), whichever comes first. Record the inspection information in the CNG Fuel Tank Inspection Record. The CNG Fuel Tank Inspection Record is located in the owner's manual supplement.
    • Do not remove the tank from the vehicle for general inspections. Tank removal is only necessary if the following conditions are present:
       - The tank has been exposed to corrosive chemicals such as acid or alkali.
       - Unusual corrosion is observed in the bed area.
       - Obvious damage is observed in the bed area.
       - The tank straps are loose or damaged.
       - The vehicle has been involved in a collision and damage is observed in the tank area.
    • Ensure the tank cover is in place and intact. Never operate or store the vehicle outside with the tank cover removed. The CNG tank wrap can be damaged by extended exposure to ultra-violet (UV) radiation. Extended exposure to UV radiation can cause the folllowing conditions:
       - loss of label legibility
       - loose fibers as the epoxy resin degrades
       - chalking of the epoxy coating
    • If the tank is replaced, perform the following steps:
        1. Obtain a new CNG Fuel Only label.
        2. Obtain a new Bi-fuel Information label.
        3. Record the new tank service expiration date (the date of the manufacture plus 15 years) on both labels.

Tank Label Inspection Procedure

Verify that the CNG fuel tank label is in place.

Contact the GM Technical Assistance Center (TAC) if any of the following conditions exist:

    • The label is not readable.
    • The label is peeling.
    • The label is missing.

Verify that the tank expiration date matches on the tank, the tank cover, and the underhood labels. If needed, replace the tank cover and the underhood labels so the expiration date matches the tank label.

Tank Wrap Inspection Procedure

Important: Cracking or splitting of the carbon fiber wrap around the circumference of the tank may occur during manufacture. This is normal. It does not affect tank strength and does not require repair.

A carbon fiber epoxy matrix hoop wrap protects the CNG fuel tank. Inspect and resurface abrasions or cuts as follows:

Level 1 Abrasions:

    • Level 1 abrasions are minor abrasions such as scuffs that are less than 0.25 mm (0.010 in) deep.
    • It is not necessary to resurface Level 1 abrasions.

Level 2 Abrasions:

       Important: Replace tanks with abrasions that exceed Level 2 specifications.

    • Level 2 abrasions are abrasions with some exposed fibers or flat spots with a depth between 0.25-0.76 mm (0.010-0.030 in).
    • Resurface Level 2 abrasions before returning the tank to service.

       Important: Cut away frayed fibers before application of the epoxy coating.

    • Resin coat the abrasion with any commercial room temperature cure 2-component epoxy resin (Loctite® P/N 14600 or equivalent).

Level 1 Cuts:

    • Level 1 cuts are cuts or scratches that are less than 0.50 mm (0.020 in) deep.
    • Level 1 cuts may be any length.
    • Level 1 cuts may be in any direction.
    • It is not necessary to resurface Level 1 cuts.

Level 2 Cuts:

       Important: Repair Level 2 cuts before returning the tank to service.

    • Level 2 cuts are cuts or scratches that are up to 0.76 mm (0.030 in) deep.
    • Level 2 cuts are up to 203 mm (8.0 in) long.
    • Resurface Level 2 cuts before returning the tank to service.

       Important: Cut away frayed fibers before applying the epoxy coating.

    • Resin coat the cut with any commercial room temperature cure 2-component epoxy resin (Loctite® P/N 14600 or equivalent).

Metal Tank End Inspection Procedure

A multi-coat paint system with a zinc-rich primer protects the metal tank. Inspect and recoat chips in the paint as follows:

Level 1 Chips:

    • Level 1 chips are chips or abrasions in the coating that do not penetrate the black top coat.
    • Level 1 chips do not expose the gray zinc-rich primer.
    • Level 1 chips do not require resurfacing.

Level 2 Chips:

    • Level 2 chips are chips or abrasions that penetrate the black top coat.
    • Recoat Level 2 chips or abrasions in order to prevent corrosion
    • The following 2 repair methods are recommended depending on whether the zinc-rich primer is still intact:

Method 1:

      • Recoat the chip using any commercial room temperature cure 2-component epoxy resin (Loctite® P/N 14600 or equivalent) if the chip has not penetrated the zinc-rich primer.
      • This is the same material used to repair Level 2 tank wrap damage.
    • The following procedure is recommended if the chip has penetrated the zinc-rich primer and exposed the bare metal:

Method 2:

      • Sand the damaged area in order to remove any rust and to rough-up the surrounding coating.
      • Clean the damaged area with a commercial prepaint cleaning solvent (Dupont® Prep Sol or equivalent).
      • Apply a zinc-rich cold galvanizing primer (LPS® P/N 00516 or equivalent).
      • Coat the area after the primer has cured using a room temperature cure 2-component epoxy resin (Loctite® P/N 14600 or equivalent).

Dents

Important: Replace tanks with dents to the metal edges greater than 1.52 mm (0.060 in) deep.

Gouges

Important: Replace tanks with sharp gouges penetrating the paint and the metal.

Transition Area Corrosion

Transition area corrosion occurs where the tank wrap meets the metal tank end. A multi-coat paint system with a zinc-rich primer protects the metal tank. Inspect and recoat corrosion as follows:

    • Sand or wire brush the affected area to remove as much rust and debris as possible.
    • Clean the damaged area with commercial prepaint cleaning solvent Dupont® Prep Sol or equivalent.

       Important: Follow the instructions as supplied with the rust converter treatment.

    • Brush apply a commercially available rust converter such as Vappro® Magtan or equivalent to the transition area along the circumference of the tank.
    • Apply zinc-rich cold galvanizing primer LPS® P/N 00516 or equivalent.
    • Apply a coat of black enamel spray paint such as Rustoleum® or equivalent and let dry.
    • Apply a second coat of black enamel spray paint such as Rustoleum® or equivalent.

Mounting Bracket Inspection Procedure
  1. Verify that the rubber isolator is properly seated on the tank brackets and straps.
  2. Inspect the rubber isolator for cracks, deterioration, or other damage.
  3. Replace the rubber isolator if necessary.
  4. Inspect the tank brackets, straps, mounting frame, and mounding hardware for cracks, corrosion, deformation, or other damage.
  5. Replace if necessary.

Removing From Service
    • The CNG fuel tank has a fifteen year service life from the date of manufacture.
    • The CNG tank manufacture date appears on a label on the tank.
    • The tank expiration date is on the CNG Fuel Only label and the Bi-fuel Information label.
    • Any tank in service for 15 years or more must be removed from service using the following procedure:
        1. Remove and vent the tank. Refer to the latest service procedures.
        2. Disconnect the vent hose.
        3. Allow the tank to stand for 24 hours with either the tank valve energized or the manual valve opening tool installed.
        4. Place the tank outside in a well ventilated area.
        5. Drill a 1/4 inch hole after the last digit of the tank identification number stamped into the valve end of the tank.
        6. Dispose of the tank in a safe and approved manner.