A/T - Methods to Check for Restricted Exhaust

TSB 87-36 (June)

SUBJECT: GM RESTRICTED EXHAUST SYSTEM CHECK

PROBLEM:
Late shift, sometimes no maximum throttle upshift.

POSSIBLE CAUSE:
Restricted exhaust system due to bent or collapsed pipe
or plugged catalytic converter.

POSSIBLE SOLUTIONS:
Figures # 1 and # 2 show ways to check for restricted exhaust system.

FIGURE 1




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

2. Connect a fuel pump pressure/vacuum gauge to a hose and nipple.

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

4. With the engine idling at normal operating temperature, observe the exhaust system backpressure reading on the gauge. Reading should not exceed 1 to 1-1/2 PSI.

5. Accelerate engine to 2000 RPM, and observe gauge. Reading should not exceed 3 PSI. If the backpressure, at either RPM exceeds specification1 a restricted exhaust system is indicated.


FIGURE 2




1. Carefully remove oxygen sensor.

2. Install Borroughs exhaust backpressure tester (BT 8515 or or equivalent in place of oxygen sensor).

3. With the engine idling at normal operation temperature, observe the exhaust system backpressure reading on the gauge. Reading should not exceed 1 to 1-1/2 PSI.

4. Accelerate engine to 2000 RPM and observe gauge. Reading should not exceed 3 PSI of backpressure, at either RPM, exceeds specification, a restricted exhaust system is indicated.

5. After completing test, be sure to coat threads of oxygen sensor with anti-seize compound P/N 5613695, or equivalent prior to re-installation.