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Registered
2000 2.5rs brp
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25 Posts
Discussion Starter · #1 ·
I have noticed of late im getting semi poor gas mileage. recently changed the oil put new plugs in and ever since im getting bad gas mileage. I filled it up On 11.5 gallons and im less than half a tank now and i have been 150 miles. I have noticed that if i drive the car and say its 3/4s full and park it my gas will will be below the 3/4 mark when i get back in it. I looked for leaky lines and cant find any leaks and nor do i smell gas. Do you guys have any ideas on what could cause the bad mpgs and the disappearing gas
 

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Modsterdomus
2000 STM RS Sedan 5spd
Joined
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7,849 Posts
I thought the same thing, gap the plugs properly. Make sure you bought the right plugs. NGK makes our stock plugs last i checked.

Also, if you cross threaded the plugs you could be getting blow by or something. I hope they threaded in easily, if not you could have butchered your heads.

Make sure the wires are on securely. A bad connection will make for weak spark.
 

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Registered
2000 2.5rs brp
Joined
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25 Posts
Discussion Starter · #5 ·
I used ngk plugs stock gaped the plugs to .44 like it said and the only cel i have is rear o2 sensor and knock sensor im fixing the rear o2 sensor this weekend and also knock sensor when i can find one. plugs went in easy and wires are on tight.
I was getting 375-400 on a full tank when i first got the car
 

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aka obs111
2004 WRB WRX
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970 Posts
Sweet. That may be a good thing that you have a CEL for o2 sensor. Change that and I'm thinking that will most likely fix your low gas milage issue.
Your car will start to consume more gas than it usually does. A malfunctioning 02 sensor can result in the air-fuel mixture to run either too rich or too lean which in some cases can result in poor MPG.
 
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