Restricted Exhaust Check

RESTRICTED EXHAUST SYSTEM DIAGNOSIS

A partially restricted or blocked exhaust system usually results in a loss of power or backfire up through the throttle body. Verify that the condition is not caused by ignition or fuel system problems, then perform a visual inspection of the exhaust system. If the condition cannot be located by visual inspection, perform the following procedure.

- Attach a vacuum gauge to the intake manifold.

- Connect a tachometer to the ignition coil negative (TACH) terminal.

- Start the engine and observe the vacuum gauge. The gauge should indicate a vacuum of 16-21 inches Hg.

- Increase the engine speed to 2000 rpm and observe the vacuum gauge. The vacuum will decrease when the speed is increased rapidly, but should stabilize at 16-21 inches Hg and remain constant. If the vacuum remains below 16 inches Hg, the exhaust system is restricted or blocked. Stop the engine and proceed to the next step.

- Disconnect the exhaust pipe at the manifold.

- Start the engine and increase the speed to 2000 rpm. Observe the vacuum gauge.

- If the vacuum stabilizes at 16-21 inches Hg, restriction or blockage is either in the exhaust pipe, catalytic converter, muffler or tail pipe.

- If the vacuum stabilizes below 16 inches Hg with the exhaust pipe disconnected, the exhaust manifold is restricted.

- Stop the engine, connect the exhaust pipe and remove the muffler. Start the engine and increase the engine speed to 2000 rpm. Observe the vacuum gauge.

- If the vacuum stabilizes below 16 inches Hg, the restriction is in the catalytic converter.

NOTE: In the event of a catalytic converter failure, always inspect the muffler and ensure converter debris has not entered the muffler.

- If the vacuum is normal, the muffler or tail pipe is restricted.

- Stop the engine.

- Disconnect the tachometer and vacuum gauge.