Terrible MPG, Bad Cat, Running Rich + more

Hey 6ga,

So I've been getting terrible gas mileage lately... Maybe 10-15 mpg city and 20 mpg highway, and it's becoming a huge problem.

I know that my cat is gone because 8 months ago before I swapped my engine with another f23a1, it was rattling like crazy on the inside when I idled. After doing the swap, I haven't heard much of anything.

So I read the live data from my o2 sensors and I found that my upstream was staying above .65 mV and was fluctuating between that on the low end and .95 mV on the high end which is super rich. However, I then noticed that my downstream o2 sensor was sitting at .075 and fluctuated between that and .091, but I do have an exhaust leak before the cat and it might be clogged (I took 50 frames of data).

Let it be known that I have a p0420 and a p0430 code CEL right now.

Let it also be known that I have a magnaflow high flow cat and I'm going to be replacing my whole entire exhaust system next week from the header back (stock except the cat). Do you think doing all of this will increase my mpg and turn off my CEL?

I'm just tired of this thing running rich, and I'm afraid that if this doesn't fix the issue, then it'll ruin this catalytic converted that I'm going to put on.

Any thoughts?

EDIT: I've already searched through the forums for answers to this, my case is just a bit unique.

Not sure how you have a P0430 on a car with only one cat...

You could be running rich for a number of reasons. Bad injector, vacuum leak (usually causes a lean code but worth checking), or air limitation (exhaust) and primary O2 sensor. On the F23A1, the primary O2 sensor is very cheap and worth replacing. Secondary O2, don't replace if there isn't a code. That O2 serves the purpose of telling whether the cat is good or not. That's it.

james'99 said:

Not sure how you have a P0430 on a car with only one cat...

You could be running rich for a number of reasons. Bad injector, vacuum leak (usually causes a lean code but worth checking), or air limitation (exhaust) and primary O2 sensor. On the F23A1, the primary O2 sensor is very cheap and worth replacing. Secondary O2, don't replace if there isn't a code. That O2 serves the purpose of telling whether the cat is good or not. That's it.

Click to expand...

Well, I already replaced the upstream o2 sensor, on my other engine, and swapped the sensor over during the swap. Maybe I should take it out and have a look at it?

Also, I bought the secondary o2 sensor with the cat that I bought like a year ago, so I already have it all.

One thing I've noticed is that when I cold start my engine and I open the hood, I can hear a ringing as if my ears were ringing. Just a very high tone but its very quiet. I'm not sure what that could be either.

I feel as though my cat is definitely plugged though (the whole exhaust thing you're talking about), so since I already have my exhaust parts coming in I guess I'll just replace it all and see what happens..