# Gas mileage



## am3rican (Feb 26, 2005)

My car has been throwing the P0420 code lately. its a 2001 Nissan Maxima SE 5spd w/ 38K miles. Well, the dealer told me my exhaust pipe (the y-pipe) needs to be replaced at a cost of $900, which i think is BS because my "service engine light" hasnt come back on in over a week.

Well, Ive been getting about 21-22 mpg, even though I drive 90% of my miles on the highway @ 75-80 mph. Now, being a 5spd, its rated at 22, 27 for city and highway. 

Does anyone know what i can do to increase my gas mileage and whther the Y-pipe has anything to do with my gas mileage? and could it be that my exhaust sensors are bad and thats why im getting such crappy mileage? Will the dealer do a diagnosis for free concerning gas mileage if i have an extended warranty?


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## 96_vqmax (May 14, 2003)

Well are you mod or stock?How's your car driven?


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## Stephen Max (Aug 18, 2003)

A common source of bad mileage is an air leak in the exhaust close to the O2 sensors. The sensor detects the extra O2 and the ecu thinks the afr is lean. The ecu then tries to compensate by adding fuel, resulting in a rich afr and crappy gas mileage.

So it is very possible that the y-pipe has a bad O2 sensor fitting that leaks air, or a warped flange, but it may also be true that the problem may be at the header mounting flange, or it may just be that you need a new crush gasket between the y-pipe and the header. Or it may just be that you need new O2 sensors.

At any rate, you can get an aftermarket y-pipe installed for much less than $900.


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## am3rican (Feb 26, 2005)

96_vqmax said:


> Well are you mod or stock?How's your car driven?


completely stock...and...it's driven well...like a normal person. i very rarely rev the motor past 3 or 4 grand.


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## am3rican (Feb 26, 2005)

I got a call from some lady at Nissan's consumer affairs and she said the warranty department is checking to see if the ypipe is covered under the federal emissions warranty. she said shed call me back tomorrow. she also said that if it is not on the warranty, i would have to pay for it out of my own pocket


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## 96_vqmax (May 14, 2003)

am3rican said:


> completely stock...and...it's driven well...like a normal person. i very rarely rev the motor past 3 or 4 grand.


If you're stock,then I'ld think maybe your y pipe's leaking might cause your car to burn more fuel like Stephen Max said,have you check for other code,maybe bad O2 sensor,or maybe your driving habbit?Just like my bro 03 6sp,he never get more than 21mpg,even he drive like a grandpa,but when his wife drive it,she were able to get 24-25mpg.


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