The Pulse Air System consists of a computer-controlled vacuum solenoid (One of three on a bracket atop the rear of the valve cover), a vacuum-operated air valve (pictured at the right), a reed-type checkvalve (pictured below), and some tubing. Injecting air into the exhaust pipe or catalytic converter aids in the further oxidation of partially burned hydrocarbons. This system is used instead of the air pump found on many engines.

There are two identical assemblies, one on each side of the engine (on the 1987 through 1990 YJ Wrangler these may both appear on the passenger side of the engine). The one on the driver's side injects filtered air into the the catalytic converter (downstream), and the one on the passenger side injects air into the exhaust pipe just below the exhaust manifold (upsteam). This picture shows a shiny new check valve next to an older (but still functional) rusty one.

DETAILS

Here is one side of the Pulse Air System. It relies on pressure pulsations in the exhaust stream and a one-way checkvalve to draw air down from the air cleaner. When it feels like it, the computer actuates the vacuum solenoid which actuates the air valve, allowing air to flow from the filtered side of the air cleaner down through the reed-type checkvalve to the catalytic converter or exhaust pipe. The checkvalve should not allow exhaust to flow up the tube into the air cleaner , or bad things happen.
With the engine warm and idling, and with the lid off the air cleaner, it is easy to hear the Pulse Air tubes resonating when they are energized. Holding your hand over them you can feel the pulsing. However, the overall pressure is negative. If you jam a vacuum gauge into the tubes inside the air cleaner, you should find that they will pull an inch or two of vacuum.

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