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Discussion Starter · #1 ·
Hi Guys,

Recently my 02' 9-5 Linear 2.3 LPT with 107K original miles is getting average 19.5 MPG combine. I was getting average about 23.5 MPG combine. I have replaced numerous parts and vacuum hoses and and fresh tune-up, but the MPG remain the same. The one replacement I've done recently are the tires. Four (4) brand new Bridgestones G019 tires. The car idle and runs perfect. The boost is just right, meaning it doesn't go into the red zone if I gun it, just barely touch the starting point of the red zone.

I thought my SID was wrong and non-function when comes to fuel calculation, so I used the manual receipt, miles calculation method and came up with the same average MPG.

I drive normal and no, I don't have the lead foot unless, I get on the on-ramp to merged into traffic.

I do have the PCV #6 upgrade last year and I use nothing but Mobil 1 (5w30) throughout the year and flushed it every 4K miles.

Anyone here have a clue where I should be looking at? Oh yeah, no codes at the moment. no leak, or smoke.

Any ideas??

Help!!

J
:cry:
 

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how long ago were you getting 23? mileage goes down noticeably during winter. i was doing about 21mpg ALL CITY in the summer and im getting maybe 19.2-19.5 now during the winter. Its just starting to bump itself back up. i do GO for gas mileage in most of the city, though.

has your daily route changed at all? stop and go constant city is a LOT different than hitting a few stop lights but mainly staying moving (cant think of how to explain it)

I'd do a new fuel filter and throw some cleaner in there during your next fill up and see if that helps.
 

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Discussion Starter · #3 ·
noticibably worse during cold winter months, but not this bad though. My daily routes are exactly the same. I did do the fuel filter replacement in November of 2009 and I often used Techron fuel injector cleaner. I did checked the air filter in June/July of 2009 and it was like new.

I can't imagine that the new tires has that much restriction as the older tires I had on there. It's properly aired since I had the shop double-check the air pressure as well. The emergency brakes are not sticky, because I tested it while the rear of the car jacked up.

I might go with a new O2 sensor in spring, but again, no codes as I can see.

???

Thanks for your response.
 

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noticibably worse during cold winter months, but not this bad though. My daily routes are exactly the same. I did do the fuel filter replacement in November of 2009 and I often used Techron fuel injector cleaner. I did checked the air filter in June/July of 2009 and it was like new.

I can't imagine that the new tires has that much restriction as the older tires I had on there. It's properly aired since I had the shop double-check the air pressure as well. The emergency brakes are not sticky, because I tested it while the rear of the car jacked up.

I might go with a new O2 sensor in spring, but again, no codes as I can see.

???

Thanks for your response.
hmmmm....possibly the MAF then. if that gets dirty itll get a poor airflow reading and can cause you to use too much fuel or too little. its really easy to pop off and clean it. Check the throttle body as well.

make sure ALL vacuum connections are secure and there are no loose hoses. this is another known cause of poor MPG.
 

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Discussion Starter · #5 ·
No loose vacuum hoses for sure - I used the old fashion method by spraying carb cleaner around the engine area and see if the idle changes or not. in this case, it did not.

I will check the MAF this weekend if the weather permits.

Thank you.
 

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Are your replacement tires the same size as the old ones? Just changing from worn to new tires will decrease your mileage by 2 to 3 %, due to the larger diameter of the new tire (tire diameter changes about 1/2" when worn). If a larger diameter tire were installed, the mileage would also be reduced further. This link will tell you the difference in diameters if you have the tire info. This won't account for all of your mileage loss, but may be a part of it.

http://www.miata.net/garage/tirecalc.html
 
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