Q: Slight smell of gas or oil and poorer mpg fuel efficiency

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A few days ago I started noticing a slight smell of gas or maybe oil at the back of my car. I just got it out of the body shop after a minor front bumper repair. The gas mileage has gone down significantly, from approximately 19 mpg to 15-16 - and I've been driving much slower and more carefully! It's about time for an oil change but not enough for the smell. I'm maybe a 6,000 mikes on a semi synthetic blend, if that

My car has 98700 miles.
My car has an automatic transmission.

This may be a result of a faulty oxygen sensor. As you may know the oxygen sensors which are part of your emissions system read exhaust gases to determine whether or not the appropriate amount of oxygen is present in the exhaust. Based upon this reading, this information is relayed to the car’s ECU which then makes a determination as to whether or not to add more or less fuel to the engine. When too much or too little oxygen is present, this will cause check engine light to come on. Too much oxygen may be present in the exhaust gas due to things like an exhaust leak, a vacuum leak, a faulty mass air flow sensor (causing a lean fuel condition) or faulty fuel injectors. Too little oxygen may be present in the exhaust gas may be caused by things like a clogged air filter, a failing mass air flow sensor (causing too much fuel to be introduced to the motor), bad fuel injectors or a clogged catalytic converter. When the O2 sensor is not working properly, this will cause false readings to be relayed to the computer causing inaccurate adjustments to be made to the intake and fuel system in your engine. You may also notice a very strong smell of fuel and poor fuel mileage. I would suggest having an expert from Your Mechanic come to your home to diagnose your emissions system.

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