Exhaust System Backpressure
WARNING: This page does not describe the selected car, but rather 11 other vehicles, including the 2003 Mercury Sable, 2003 Mercury Marauder, 2003 Mercury Grand Marquis, 2003 Lincoln Town Car, and 2003 Lincoln LS. However, it is still accessible from the selected car via links, so may be relevant.
The exhaust system can be checked with a vacuum or pressure gauge. If using a pressure gauge, remove oxygen sensor or air injection check valve (if equipped). Connect a pressure gauge. Typical exhaust back pressure (when measured near the exhaust manifold and at normal engine operating temperature) should not exceed 3 psi at idle and 8 psi at wide open throttle under load.
If using a vacuum gauge, connect vacuum gauge hose to intake manifold vacuum port. Start engine. Observe vacuum gauge. Open throttle part way and hold steady. If vacuum gauge reading slowly drops after stabilizing, check exhaust system for restriction.