LACK OF WARM AIR FROM HEATER CHECK INTAKE MANIFOLD PASSAGE

VEHICLES AFFECTED: 1987 'R' AND 'V' TRUCK WITH 5.0L L03 AND 5.7L L05 ENGINES (VIN CODES H AND K)

Early production 'R' and 'V' trucks equipped with L03 and L05 engines that were built at the Janesville, plant may have a blockage in the inlet manifold that could restrict coolant flow to the heater core. This could lead to customer comments of low or no heat from the vehicle heater.

This condition was repaired after production sequence numbers J103535 for Chevrolet units and J501393 for GMC units.

If a vehicle is in with a no heat condition and the production sequence number is prior to the repair date, the following manifold repair procedure should be used. (Refer to the Illustration for additional details).

1. Remove. plug from inlet manifold located to the left and rearward of the TBI unit.

2. Probe with a .318 inch (approximately 5/16") rod. Rod should drop into hole to a depth of 10 cm (4 inches).

3. If probing shows no blockage, the plug should be replaced after applying thread sealant.

4. If blockage is found (i.e. probe will only go to a depth of 7.5 cm), continue with the following steps:

5. Drain all coolant from radiator.

6. Insert a 7/16" diameter rod into hole and tap with hammer to break blockage free, being careful to try to trap the broken free material at the bottorn of the hole.

7. Using a wet vacuum with an 11/16" diameter suction hose inserted through hole, retrieve broken free material by first starting wet vacuum then pressurizing cooling system through radiator cap to 15 P.S.I.

8. Verify hole is open by re-probing with .318 diameter rod.

9. Re-install plug and refill system with coolant.

10. Verify heater operation.

NOTE: IF "BROKEN FREE" MATERIAL CANNOT BE RETRIEVED, THE INTAKE MANIFOLD SHOULD BE REPLACED.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.