Exhaust System BACKPRESSURE Check
WARNING: This page is about a different car, the 1990 Saab 9000 and 1990 Saab 900. However, it is still accessible from the selected car via links, so may be relevant.
The exhaust system can be checked with a vacuum gauge or a pressure gauge. Remove O2 sensor or air injection check valve, if equipped. Connect a 1-10 psi gauge and run engine at 2500 RPM. If exhaust system backpressure is greater than 1 3/4-2 psi, exhaust system or catalytic converter is plugged.
If a vacuum gauge is used, connect it to intake manifold vacuum. Observe vacuum gauge. Open throttle part way and hold steady. If vacuum gauge slowly drops after stabilizing, exhaust system should be checked for a restriction.