bad mileage. Oxygen sensor?
 

I am getting bad mileage. I have changed the air filter, plugs, wires, distributer, put on bigger tires and rims, and tried to drive it gently (like a Grandma would drive). I am still getting bad mileage. I am getting about 400km out of of a fill. It is a 2.3 engine, 5 speed.
Any help would be appreciated.

I'm in the US so i don't know the metric to english conversion, but i got poor mileage when i had a 5 speed 2.3L mustang ('91). I actually get close to similar mileage with my '84 5.0L carbureted mustang (difference of about 3 miles per gallon less and 100 horsepower and 140 lb/ft of torque more with the 5.0L). I tried the same thing and was dissapointed with the gas mileage of my mustang when i had it because it was gutless and got poor mileage. Getting a new oxygen sensor may help but don't expect any miracles, it sounds like you're getting typical mileage with yours.

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'84 Mustang 5.0 LX
My car

I am currently getting very poor gas milage at idle and not so bad but poor highway milage. My 02 sensor works fine, but I found that I had a small leak in my exhaust manifold. Try checking yours for leaks while it's running, it could fix your gas milage problem. The o2 sensor in my car is at the bottom of my exhaust manifold and this is why I thought my 02 sensor was not working and wasted 75.00 to get a electronic engine alalysis done. Just to tell me that I had a crack in the exhaust manifold.

Good luck
lever_John@hotmail.com
91 ford mustang 2.3 Litre 4 Cylinder

First off i'd like to say it's funny seeing someone using 84stangLX because that used to be my username when i only had my LX and not my GT......anyways, now to the point.

I had a '91 LX 2.3L 5 speed and it would AVERAGE 21 miles per gallon, i kept track meticulously.

My '84 5.0L LX would get 16-18 miles per gallon with a 5 speed and holley non-emission 4 barrel.

My '89 GT now currently AVERAGES 19 miles per gallon.

I think the 2 mpg difference it not worth the 110 horsepower 165 ft/lb torque difference and increased handling/braking of the 5.0 package (well, increased braking in the '85+ models i believe). Welcome to the slow world of the 2.3L mustang. I believe that the 2.3L was mostly meant to lower the emissions for the mustang model line and also to attract a lower budget buyer. I was also surprised by how crappy the mileage was. Another thing that sucks is that they're gutless and the "power" if you can even call it that runs out EASILY by 4000 rpm.

While I'm admittedly not an expert on your motor, I can relay my own experience: With my RX-7 my average highway mileage went from 23mpg to 19mpg with a bad O2 sensor. When it goes bad, my ECU goes into "limp" mode so the motor runs very rich. I don't know what a replacement one costs for your motor, but for me its a mere $25 so its well worth it. Food for thought.