Initial Inspection and Diagnostic Overview

A slight pressure in the exhaust system is normal, but excessive exhaust back pressure seriously affects engine operation. Causes of high exhaust back pressure are dents or obstructions in the exhaust pipe, a plugged three way catalytic converter or muffler.
Test method (Vehicle Parked):
1. Remove oxygen sensor.





2. Insert exhaust back pressure adaptor (SA9306E) into exhaust manifold. The thread designation is M18 x 1.50.
3. Connect gage bar kit SA9127E, 0 - 15 kPa gage (0 - 60 inch H2O) to back pressure adaptor.
4. With engine at normal operating temperature, observe exhaust back pressure at 4000 rpm.
5. The exhaust back pressure must be less than 5.0 kPa (20.13 inch H2O).
Test method (Performed During Road Test):
1. Remove oxygen sensor.

NOTICE: Do not use 0 -60 inch H2O gage when performing this test, as it will be permanently damaged due to high back pressure during accelerations. Use 0 - 690 kPa (0 - 100 psi) gage and appropriate hoses in service gage bar kit SA9127E.
2. Install exhaust back pressure adapter (SA9306E) into exhaust manifold. The thread designation is M18 x 1.50.
3. Connect gage bar kit SA9127E, 0 - 861 kPa (0 - 100 psi) gage.
4. With engine at normal operating temperature, perform a 15 mph road test. Automatic transaxles should be in "D" and manual transaxles in "3rd" gear. Maximum exhaust back pressure readings are taken during short wide open throttle accelerations.
5. The maximum exhaust back pressure during wide open throttle accelerations must be less than 50 kPa (7.25 psi).

IMPORTANT: If exhaust pressure exceeds specification, inspect for a dented or collapsed exhaust pipe. It may be necessary to disconnect exhaust pipe before or behind converter and repeat Step 4. If removing muffler does not lower back pressure, disconnect three way catalytic converter from exhaust manifold pipe and repeat test.

6. Replace any part of exhaust system found to be damaged.
7. Install anti-seize on oxygen sensor's threads and install sensor. It may be necessary to disconnect negative battery terminal in order to clear any codes set while operating engine with oxygen sensor removed or disconnected.