This is an educated guess!
It probably regulates the amount of oxygen in the fuel system.
it senses the O2 level in the exhaust too much means lean too little means rich
On a 1998 Mercury Grand Marquis : Bank 2 is the drivers side of the engine Sensor 1 would be in the exhaust close to the engine before the exhaust enters the catalytic converter ( upstream sensor )
The 2003 Mercury Grand Marquis came equipped with the 4. 6L V8. Oxygen (O2) sensor locations are upstream and downstream (before and after the catalytic converters).
Bank 2 is the drivers side of your engine , Sensor 1 is in the exhaust before the catalytic converter ( upstream )
Bank 1 is the passenger side of the engine in a Mercury Grand Marquis Sensor 1 would be in the exhaust close to the engine before the exhaust enters the catalytic converter ( upstream sensor )
On a 1997 Mercury Grand Marquis : Bank 2 is the drivers side of the engine and ------------------------------------------------------------------------------------------ Sensor 1 would be close to the engine before the exhaust enters the catalytic converter Sensor 2 would be AFTER the exhaust has passed through the catalytic converter ( also called a catalyst monitor )
firewall 4 - 8 3 - 7 2 - 6 1 - 5 front of Mercury Grand Marquis
There are four, two on each side, pre- and post- catalyst.
The 1996 Mercury Gran Marquis does not have a 318 V8. It has a 281 V8 (4.6 Liter). 318 is a Chrysler engine. O2 sensors are located screwed into the exhaust system. Start at the exhaust manifold and go backward and you will find them. The cost varies from site to site. Ask you local Auto Parts store for a price quote.
Mercury Mystique with V6 engine has two oxygen sensors. First one located between radiator and engine, second - behind the engine, near the coil pack (below). It's not very difficult to replace them.
No, there is no oxygen in Mercury's atmosphere because Mercury does not have an atmosphere.
Mercury and Oxygen.
Passenger ===================================================== Actually , bank 2 is the drivers side of the engine in a Mercury Mountaineer