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Discussion Starter · #1 ·
Just you notice a drop in gas milage in gutting out your cats? I wouldn't think that doing that would cause a drop in milage since the pre-cats are behind the O2 sensors in the first gen's, 2nd gen's have total of 4.

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Honestly, I haven’t checked it, but I could see that it might happen because with your pre-cats gutted you don’t have the same restriction, or build up of gases, you had before in the area where the O2 sensor is located. Because the gases are flowing better the O2 sensor doesn’t pick up that the engine is running at the same fuel mixture it was before and may cause it to indicate to the computer that the fuel mixture needs to be richened up a bit. And a car running a richer mixture would have a tendency to burn more fuel. At least mine seems to be a bit richer when I pull it into the garage, you can smell more of a rich gas smell.

Of course I am planning on getting a split second MAS replacement and should be able to correct this problem by adjusting the split second based upon the exhaust gas temps so the car isn’t running as rich.

But of course that is also to compensate for the bigger injectors and high flow fuel pump I am planning on installing. My end goal is to install a good set of 15G’s and while gutting the pre cats and installing a high flow downpipe doesn’t necessary give you more HP it all a means to an end.

Dave Best
3Si #62
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