Quote:
Originally Posted by puddleglum
Welcome to the forum. It's possible that rebuilding your engine is part of your problem mileage wise. If you tightened everything up in the rebuild, it may take some time to break in again, just like in a new car. Also, the cracked header may be effecting the O2 sensor readings. May not be enough to through a code but enough to reduce mileage. Just brainstorming with you. Did your mileage drop after all that you've done or is the quest for better mileage something recent?
Automatics are harder in general to hypermile due to the limited driving techniques at your disposal. I found it worse when I did a lot of in town driving. Wondering if your commute might be fighting against you.
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Should I unplug the oxygen sensor and see if the mileage improves? 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. 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.