Emissions Check Valve on Jaguars, Part Two.

After last week's check valve tip, I got a request for an explanation of the system. Here 'tis:

When you start your car when the engine is cold, the fuel injection computer (ECU) provides extra fuel to keep it running until it warms up. Sort of works like the old "choke" used on carbureted cars. Unfortunately, this negatively impacts your exhaust emissions during the warm up period, so Jaguar had to come up with a way to reduce those emissions. They did that by injecting fresh air into the exhaust stream. The fresh air provided enough oxygen to allow the unburned hydrocarbons in the exhaust stream to finish burning. Once the engine warms up, the air is no longer needed, and a valve shuts off the flow of air to the air injector rail.

Now, if they just left it at that and shut off the pump, then the exhaust would force its way back up through the air injection rail and out through the pump. To prevent this, they put in the "check valve". The check valve is a one-way air valve that prevents the exhaust from backing up into the system.

Since the pump is driven by a belt, there's no way to actually turn it off. When the air is no longer needed in the air injection system, another valve switches on and diverts the pumped air into the air filter housing.

There are four major components to this emissions control system:

• The air pump
• The diverter valve
• The check valve
• The air injection rail(s)

The air flows through the system in that order. Hope this helps someone!

If you have any questions, just email us.

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