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Originally Posted by EcoCivic
Should I unplug the oxygen sensor and see if the mileage improves?
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No, that will not help you.
Quote:
Originally Posted by EcoCivic
If I understand correctly, the oxygen sensor just trims the air fuel ratio if there is a problem, and it theoretically effects nothing unless it detects that the engine is running rich or lean.
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The upstream O2 sensor provides data that helps the map in the ECU regulate fuel/air mix. That would be way important for your current problem. And if there is oxygen infiltration via a crack, it will throw the data off.
Quote:
Originally Posted by EcoCivic
This car used to get around 33-36 MPG, but around the time the old engine started failing, the mileage dropped, probably because of increased friction and reduced compression, but when I installed the rebuilt engine, the mileage did not improve again. I also noticed that when I let off the throttle on a flat road, the car starts to slow down fairly quickly, but that might just be me.
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You have a D16Y8 manifold on a D17 engine. Did you install that before or after you started noticing a fuel economy drop?