CANISTER VALVE DIAGNOSIS AND TESTING PROCEDURE. GMC Truck Caballero 1982

For 1990-2009 cars

# CANISTER VALVE DIAGNOSIS AND TESTING PROCEDURE

#### MODELS: 1982 CABALLEROS WITH 3.8L V6. 4.4L VS, 5.0L V8 OR 5.7L V8 ENGINES

THIS BULLETIN CANCELS AND SUPERSEDES 82-B-64 (AUGUST, 1982) ALL COPIES OF WHICH SHOULD BE DESTROYED.

When diagnosing a condition such ass rough idle, rich acceleration, lean idle duty cycles (an indication of rich carburetion), the following procedure should be followed for diagnosis of a canister control valve:

1. Apply a short length of hose to the carburetor bowl tube of the Type 2 canister control valve (See Figure No. 1) and blow into it. Air should pass out through the canister tube. If it does not, replace the valve.

2. Using a hand vacuum pump, apply vacuum (15" Hg or 51 kPa) to "manifold vacuum from PCV" tube. The diaphragm should hold vacuum for at least 20 seconds. If it does not, replace the valve.

3. With vacuum still applied, again try to blow through the hose into the carburetor bowl tube. No air should flow from the canister tube. If it does, the lower diaphragm assembly is not sealing correctly and the valve must be replaced.

4. Move hand vacuum pump to apply vacuum (15" Hg to 51 kPa), to the control vacuum tube, permitting vacuum to raise the upper diaphragm. The diaphragm should hold the vacuum for at least 20 seconds. If it does not, replace the valve. Seal the canister tube with a rubber cap or finger, and while vacuum is still being applied to the control vacuum tube, again try to blow through the hose connected to the carburetor bowl tube. Air should pass freely from the tube marked "manifold vacuum from PCV" (see Figure No. 1). If not, the canister control valve must 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.