Mercury Repair Questions? Ask a Mechanic for Answers ASAP
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Ok there is a front and rear and left and right on your engine, since the engine in your vehicle is in there sideways. When you look at the engine with your belly against the passenger side fender, your looking at the front of the engine. The #1 spark plug is the closest cylinder to the glove box. That is bank one. So if you lean over the fender and touch the engine with both hands. Your left hand will be on bank one and your right hand on bank 2.
Your concern is not a O2 sensor. You have lean issues. You need to start the engine cold and then open the hood and use a can of ether or starting fluid and spray SHORT bursts of ether around the intake gaskets and the air intake tube from the air filter and around all vacuum and PCV hoses. If you hit a leak the RPMS will increase. A lean code means the MAF sensor next to the air filter monitors oxygen coming in and the O2 sensors monitor oxygen in the exhaust. The computer uses the MAF sensor readings to regulate the length of time the injectors spray. So if you have a vacuum leak then more oxygen is getting i n the engine un-monitored and its causing the engine to run with not enough fuel or to much oxygen and the O2 sensors are seeing this, so there telling the computer of the issue and its dumping alot of extra fuel to compensate.
Normally this is just faulty intake gaskets which you may not get a good test on wit h the ether, other possible causes are low fuel pressure or a faulty or dirty MAF sensor.