If the system is closed loop, and the O2 sensor is good, then the mixture should either be good or a code should be thrown.
Don't understand how my fuel mpg could be 10-12 if this is working correctly. If it is using 50% more fuel than it should, I should be able to detect that by monitoring the O2 sensor, correct?

I know that there are many variables to fuel mileage, and many sensors that contribute to it, but doesn't the O2 have the final say?
Does anyone know the normal tolerance voltage range of the upstream O2?

FYI, O2 sensor is brand new NTK. New plenum gasket, CT sens, PCV, plugs, wires, dist...

Where I am going with this. I am thinking about modifying MAP sensor/CT sensor voltages in order to adjust fuel delivery. I have successfully done this with another project on my car, and I can do this for under $10. In theory, the pcm would just compensate for my mods because of the O2 sensor readings, but shouldn't it be doing that anyway?
If it comes down to it, I can also modify the O2 output. If everything worked correctly I could make the O2 read high and it would lean it out but...
Maybe dodge has a wide tolerance set for the O2 output because they had CEL problems with it tighter?

I know it is rich cause I smell it and hear it.

Any input?

 

A sound 318 pushing stock gears and tires should get much better mileage. If your gears and tires are stock or non-stock but reasonably paired, then you have a problem that is NOT a design deficiency. Troubleshooting is in order -- it makes zero sense to modify the system in a vain attempt to correct a failure.

 

1v-.9v for the o2 its a narrow band. its not very precise to determine rich or lean for tuning purposes. You can modify the map supply voltage just as if your at a higher altitude which will cut back fuel(pending which way you go with the voltage) and the pcm wont over ride it. When in closedloop the o2 only fine tunes(fuel trims) the stactic base maps. base maps then have multipliers like x map values, wot fuel enrichment, iat/cts/tps multipliers, cold start enrichment ect, that it bases it fueling, timing with. To know how good your tune(base maps) is to look at the fuel trims(pending engine condition). If the lt fuel trim is +/-10 then your base maps are off so the pcm has to pull/add fuel based of the o2 reading(closedloop). A good tune(base map) will have trims under +/-5....and fuel trims are only used in closedloop. Trims have no merit in openloop. With speed density and big cams sometimes you have to tune in openloop only.

 

I understand there is a problem, and I am working on that.
tweaker, if the o2 only fine tunes, shouldn't it throw a code at some point?
I am kind of venting, this is the only vehicle I've had where the result of anything being wrong is terrible mileage.

 

Output range is .2 to .7 volts..... .45 is right around stoichiometric. (Ideal.) When in closed loop, the PCM will adjust fuel trims to keep the O2 sensor right around .5 volt.

If you have anything else going on though.... vacuum leaks, even exhaust leaks (before the sensor)..... fuel economy will suffer.

 

10-12 mpgs is about right for in town driving on an old 5.2l.

 

Again output voltage is .1v-.9v........


Lazy o2 wont throw any code either will a plugged up o2. Need to observe the cross counts which is how fast the sensor switchs from .1v-.9v in closedloop only. Faster it switchs the faster the pcm can calculate the fuel trims and the more accurate theses calculation will be. Bad map will cause a rich/lean condition should be checked as well with a vacuum pump and DVOM. Heres a vid of what an good working o2's cross counts should be.......

http://www.youtube.com/watch?v=wPJh8...layer_embedded

 

Were you aware that a digital meter doesn't react fast enough to give an accurate reading of O2 sensor output?

Also, might wanna read this.

This one too.....

I would hate to think that all the scan tools I have used in the past were lying to me.......

Edit: Ah. .1 to .9 (missed the decimal point in front of the one.... sorry 'bout that....)

 

Please keep us posted!

I'm sharing the same frustration! See the mods listed below plus I put in cap/rotor/wires/plugs, new NTK O2 sensor and still getting 10-12 mpg. I have 285/65/16s with 3.55 gears. Getting new front and rear gears will costs too much to offset mpg. I was hoping to get mid teens with a weekend driver and I'm not a "floor it" kind of guy.

 

Id take a poll of members avg mpg...
10 to 12 would probably be th norm..
Myself...14.4 avg after sct and exhaust. Prior.12.2