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

asked by on November 27, 2016

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.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

What happen s when when my 2013 Chevy impala say reduce power engine light

The issue you are writing in about is common enough that a specific diagnostic, namely a reduced engine power diagnostic is performed by technicians dispatched by YourMechanic. If you request that diagnostic, the responding certified mechanic will get this issue...

There is a part on the throttle body that broke, where and how would I go about finding another?

if you are referring to the plastic case that contains the "throttle position sensor" (TPS), the TPS is readily available in the new aftermarket or even as a new OEM (dealer) part. The throttle body itself, and all associated parts...

2011 impala speedometer up & down while idling, car cuts off at low lidle

I think you mean that the tachometer is going up and down, not the speedometer. If the tachometer is going up and down and then the engine stalls, it's an indication that the engine has a major vacuum leak...

Related articles

What Happens If I Overinflate My Tires?
It is a common misconception that overinflating your tires will provide more responsive handling and greater fuel efficiency. In fact, over-inflation is...
Industry News for Automotive Techs: October 8-14
50 MPG Chevrolet Cruz Diesel, Mazda's G-Vectoring drive system, Uber and Volvo collaborate on autonomous cars, and Hubb's new reusable oil filter.
How Long Does a Muffler Last?
A A car is a very complicated piece of machinery. In order for the car that you have to run as intended, all of its components will have to work as intended. Taking the time to have a car inspected...