maxchao

iTrader: (2)

Finally! Team is here! Now I better behave :D

Yea I know it is really 'ONLY' 10%, not like it's something the PCM is not capable of correcting to meet the AFR target, and there is no CEL...but it bugs me...!! I think it bugs me more than if I actually have a CEL. It is like those time in school when I get a 29/30...I was almost perfect..

But then...if the O2 sensor is not reading accurate, it would be impacting my mpg right? If I can get 1mpg back I can justify the cost of a new sensor in a few thousand miles...Anyway throwing money aimlessly is still stupid I know.

HiFlite999

iTrader: (2)

Thanks Team. At first glance, as long as the LTFTs are in range, AFRs will be approximately as programmed and mileage, et al, will be normal. I'm pretty sure, however, that there's an exception to this. That would be if the front sensor has degraded enough to give a wrong AFR. With the 8, as I understand it, the rear sensor will generate a phantom trim which will attempt to trim this error. Again, if the process is "in range", the visible effects may be minimal. I think the evidence for that going on will show up as a pretty consistant offset between command and actual AFR. (Reminder: I'm not an expert on this stuff, nor claim to be).

20 mpg @ 80 mph on a 120k mile engine isn't just good, it's a miracle! That being said, it's hard to imagine that the front sensor is plumb worn out. I just changed both sensors on my 99 Toyota with 164k miles; the front was crapped up and this on a car with 100k miles between spark plug changes vs. 25k (minimum) miles on the 8. I got a boost of 5-10% in mpg's after, but it has a rather primitive fueling system and I wouldn't necessarily expect the same on the Mazda.

Yes, with proper equipment, the sensors can be tested for proper functioning. However, is the time/cost benefit worth it?

YMMV (quite literally here!)

j9fd3s

i actually haven't checked.

i tried a new MAF with no change, and my car has had a front 02, at some point, i looked for vacuum leaks without finding one

maxchao

iTrader: (2)

No the engine was replaced 20k ago, along with the cat. :P Sorry for the disappointment...

but yea I guess there is no way to tell if it's the MAF or the front O2 without some nice equipment. It can also be other stuffs of course.

I also monitored the rear O2 sensor on my Protege5 on the way to work today, and also did some research. Apparently the rear O2 sensor remains high at cruising speed is normal, since most oxygen is used in the catalytic converter. Just trying to clarify a statement I made earlier.