Fuel Economy problem on 1998 Dodge Neon

I have no idea why I am only getting 200 miles on one tank. I had it checked out and all of the scan data is fine, engine temp is fine, o2 sensor is fine, and fuel trims are good. MIL is not on.

by in Madison, WI on September 09, 2009
4 answers 2 comments
ANSWER by on September 09, 2009
Maybe the catalytic converter is clogged have a muffler repair shop check this
ANSWER by on September 09, 2009
check your tailpipe for black soot if so your fuel regulator is not working correctly assuming that you used to get more MPG
ANSWER by on September 09, 2009
Check out the .gov website http://www.fueleconomy.gov/Feg/bymake/Dodge1998.shtml you have to enter the type of transmission otherwise I would have given you the exact page link.
COMMENT by on October 08, 2009
I fixed the problem. It was in fact the o2 sensor. When i checked it, i only checked the voltage readings, i didn't check the frequency of it switching. If it has a slow frequency, then it doesn't update fuel trims in time to give good gas mileage, yet it was fast enough that it didn't flag the MIL on. Feel free to msg me if you want to know how i found this out.
COMMENT by on October 09, 2009
Congratulations on fixing your car. People fixing cars often rely to much on whether the Check Engine Light is on or not or hinging all the diagnostic trouble shooting based solely on the code flagged. Better professional grade scan tools have what is called Mode 6 diagnostic mode. Even if a code is not flagged or a sensor value is marginal Mode 6 displays binary code information in a very raw form, it is not well documented or supported by the auto manufacturers but it is where good auto techs are fixing problem cars.
ANSWER by on October 15, 2010
I had similar problem when I bought my 98 Neon. I started out with 17 MPG, replaced the front O2 sensor. It jumped up to 22 MPG so replaced the back one too and my miliage has been great ever since. I get tween 30 and 40 MPG depending on conditions. On a clear day no traffic and straightway driving on Interstate on a trip i can get almost 40 MPG... around the city i get tween 30 and 35..a well maintainted car can make a differece. I do regular maintence and watch my miliage every time i fill up..just mileage alone can be a good indicator just like it was in the older cars that did not have computers and such...
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