For 1990-2009 cars

# POOR ENGINE PERFORMANCE PLUGGED DUAL BED CATALYTIC CON

#### Subject: DIAGNOSING RESTRICTED EXHAUST SYSTEMS - ALL 1981-1982 VEHICLES EQUIPPED WITH SINGLE OR DUAL BED BEAD CATALYTIC CONVERTERS AND A.I.R.

Proper diagnosis for a restricted exhaust system is essential before any components are replaced. The following diagnostic procedure is recommended:

1. Remove the rubber hose at the exhaust manifold A.I.R. pipe check valve. Remove check valve.

2. Connect a fuel pump pressure gauge to a hose and nipple from a Propane Enrichment Device (J26911) (see illustration).

3. Insert the nipple into the exhaust manifold A.I.R. pipe.

4. With the engine at normal operating temperature and running at 2500 rpm, observe the exhaust system backpressure reading on the gauge.

5. If the backpressure exceeds 2% psi, a restricted exhaust system is indicated.

6. Inspect the entire exhaust system for a collapsed pipe, heat distress, or possible internal muffler failure.

7. If there are no obvious reasons for the excessive backpressure, a restricted catalytic converter should be suspected, and replaced using current recommended procedures.

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.