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Q: What would be the common or uncommon causes for gas mileage to drop by almost 50%?

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In the past, I was getting between 16 to 20 mpg and when I checked it 1 week ago, it had dropped to 10.5 mpg.

I do not see any signs of an obvious gas lead.

The brakes were checked 1 year ago.

New tires were installed 6 months ago.

It was inspected 3 months ago - everything OK.

The engine did "sputter" about two weeks ago. I added two cans of "heat" and the sputtering ceased.

I am not experiencing a loss of power.

Occasionally, it takes longer to start (normally, I turn the key and it starts. Now, on intermittent occasions it may take up to 3 to 4 seconds to start).

Occasionally, I will briefly detect a smell of raw gas shortly after it starts.

If you have further questions, let me know: searlyrizer@aol.com

What can I do?

Thank you,

V. Wayne Skattum

My car has 95000 miles.
My car has an automatic transmission.

Hi Wayne, There are a number of things that can cause poor fuel mileage. A faulty camshaft position sensor is one of them. The camshaft position sensor is a magnetic sensor that monitors camshaft speed to regulate ignition timing and fuel injection timing. It gathers and sends information about the car’s camshaft speed (and as a result the position of each piston) to the car’s electronic control module. This information is received by the computer, which then uses this data to further calculate the time of ignition and the timing of fuel injection required by the engine. When this is not working properly, you may experience a drop in power, poor idling, poor fuel mileage and problems starting the vehicle.

A clogged or dirty EGR valve may also cause poor fuel mileage. The EGR valve is a small component designed to allow the flow of exhaust gases into the intake manifold in controlled amounts. As such, it’s a simple valve that closes and opens as needed. The EGR valve has one single job to do, regardless of the system configuration, type of control and number of sensors: that is, to either open and direct exhaust gases into the combustion chamber, or to close and keep them from entering. Whenever you start the engine, the valve comes alive and waits in a closed position, blocking the flow of exhaust gases. Once the engine reaches operating temperature and speed increases, the valve, either through vacuum or electronic control will gradually open, allowing burned exhaust gases to enter and combine with the air-fuel mixture inside the combustion chamber. When the EGR valve is clogged or dirty, as they are prone to, it may not function properly causing the engine idle rough, stall at idle speeds, cause the car to get poor fuel mileage, or emit a strong smell of fuel due to excess hydrocarbons which also results in failing emissions tests.

A clogged or failing catalytic converter can also cause the vehicle to have poor fuel economy. As you may already know, the catalytic converter converts toxic exhaust gases into less harmful pollutants that are suitable to be expelled into the atmosphere. When this is clogged, this causes these gases to be backed up into the exhaust system not allowing the engine to breathe properly (think of a backed up sink). When this happens, the engine is forced to work much harder to expel these gases. This often results in the engine bogging down, hesitating, shaking and causing very poor fuel economy. I would recommend having a professional from YourMechanic come to your location to diagnose and inspect your vehicle.

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