# Mileage Low



## kshah (Nov 24, 2010)

Hi Guys

I have a 2005 Nissan Altima 2.5S. Recently I have seen that my average has gone down to 20miles/gallon from 29miles/gallon. Is there something wrong with the vehicle. 

Could you suggest something. Thanks


-kshah


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## Nickaltima (Jan 11, 2008)

where do you live? because i know when winter time comes around my area my car gets about 7-10mpg less because the cold air is causing it to burn more fuel..but there can be many factors causing you to loose mpg like this...how you drive if you drive city or highway mostly if you have poor grade fuel or not using premium in a 3.5 or if there premium isnt up to par your timing could have jumped causing the A/F ratio to change making it run rich which leads to dumping more fuel into the motor..but it sounds to me something like that possibly a sensor going bad causing it to run rich..your best bet it to take it to a reputable mechanic and have it diagnosed and hopefully they can find out the problem..good luck


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## sggs (Aug 24, 2011)

dirty injectors, vacuum leak( but you'd probably have more symptoms), clogged exhaust/catalytic converter. i recommend using fuel injector cleaner on a regular basis.


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## techtalk (Jun 8, 2011)

Kshah,

There is a plethora of reasons why your fuel mileage has dropped so dramatically as of recently. Let's cover all of the most commonplace causes for a drop in fuel efficiency:


Oxygen sensors- An improperly functioning oxygen sensor can to lead to poor gas mileage. I've read that fixing an oxygen sensor may improve your car's gas consumption by as much as 40 percent. Inspect the oxygen sensor in your Altima and if it is foul then replace it.

Ignition system components- Things like the ignition wires, spark plugs and the ignition timing of your engine affect your fuel mileage. When was the last time that you replaced the plugs or wires on your Altima? If it's been over 30,000 miles since you last changed the plugs or wires on your vehicle then it is high time that you inspect these ignition components for wear. Replace accordingly.

Air Filter- Routinely replacing your car's air filter will guarantee that your engine is achieving maximum fuel efficiency. The owner's manual recommends that you replace the filter element every 30,000 miles; however, you may want to consider replacing it sooner if you live in a particularly dusty environment. (refer to this Altima Air Cleaner diagram for an illustration of all relevant components) 

Vacuum Hoses- Inspect all of your Altima's vacuum hoses to ensure that there are no kinks or leaks that may cause poor fuel efficiency. 

Fuel Injection system- Fuel system components such as the injectors, the fuel pump and sometimes the fuel filter can cause your fuel mileage to severely drop should they become fouled. Inspect the injectors and fuel pump to ensure that the fuel pressure is adequate. 

Compression test- In extreme cases, your engine's cylinders could be operating at improper compression levels, therefore causing poor engine performance and fuel efficiency. Have a skilled mechanic perform a compression test on your Altima to ensure that each cylinder's compression is within the specified range.

Tire pressure- Routinely checking the pressure of your car's tires will help maintain good fuel mileage. Consult your owner's manual for the proper pressure for each tire.


There are a few other "bad fuel mileage components" on the check-list but this should get you started


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## Paul79UF (Jan 23, 2003)

A good bottle of injector and fuel system cleaner might help. 

If not, look into replacing the spark plugs and PCV valve.

Let us know how it goes.


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