So, my fuel trims were all over the place before my cat exploded but mostly really rich. I'd reset the car with the brake stomp, or a battery reset and it'd run good for a while. Before it failed, it had various pending codes P0410/11, P420, P0172, and saw a P2097 pending once that went away. The only faults that triggered the check engine were the P0411 and P0420 after it popped lol.

Car still starts hot and cold within 1 to 1.5 seconds after gutting cat. Car pulls fine and no misfires and okay vacuum seen through intake. It has 109k miles for which I have owned since 106k. I have a newer BHR ignition which I tested with a HEI Spark tester not too long ago (before the cat exploded) as I thought maybe a coil was bad and responsible for my weird fuel trims. An o2 sensor was replaced at 86k but idk which one. My plugs have like 1500 miles on them.

I have noticed through the torque app that on start up for a few seconds it says under fuel status "system failure" along with the loop, forgot if it was open or closed.

The car is still running a bit funny intermittently at idle or when I stop and maybe I noticed some strange feeling on freeway in closed loop, but I can still accelerate to 140 smoothly when pushed. Not sure if I have to wait for computer to relearn after brake stomp or if the O2 sensor is bad but not throwing a code. Or possibly something else with this nightmare car lol.

 

Can you be more specific about the fuel trims? They're supposed to jump around as you drive.

p0420 should have been your first clue, the cat was due to be replaced then.

 

Yeah..., the pending 420 code only showed up when I checked it in a lowes parking lot cause it was bogging down, then like 4 miles later the light came on and the car turned off at a stop sign 1 mile from my house.

The STFT would trend towards -25 eventually dragging down the LTFT when the cat was in but a reset made it work well for awhile. Replaced the Eccentric Shaft sensor too, when I first installed the BHR ignition the LTFT was happy at 3.9 for a year until I started getting the STFT going between -25 and 25 without much throttle input under closed loop on freeway. Like one time on freeway the STFT just went to -25 and stayed there and got a system too rich code but nothing for o2. The last time I took it out after gutting the STFT went to -25 and stayed there and the LTFT went to -18 or so. After driving like 30 min or so, after restarting car then the LTFT started to drop and the STFT got off -25 and went to something more normal oscillating around 0 again for a bit. I haven't driven it further since then cause I don't want to damage something or get stuck. Idk if the sensor works better after driving it awhile or what.

 

The ECU runs diagnostics on the O2 sensor every timr you drive, to see how it responds to slight changes in fuel mixture, and if the responses are slow or erratic it will throw an O2 sensor code. Since it hasn't done that, my guess is the sensor is right and your fueling is actually fluctuating, maybe due to a sticking injector or MAF/baro problems. You could try a new sensor but I'd be surprised if that fixed it.

What are the fuel trims, rpm and airflow g/sec while idling fully warmed up, not driving?

 

These are the readings at around 825 rpm +-25 since it fluctuates a bit.


Today when I drove, it did not get stuck at -25 on the STFT. When leaving the bank, I captured the fuel status errors, and it did not show up when I first left the house. It says open loop(system fail) then closed loop 1 O2 sensor(fault) then disappears.



Not sure what it means then if anything.

 

The MAF rate g/sec for 825 rpm is too high, it should be 5.5-ish. Feels like it thinks its getting more air than it is, and then dialing back the fuel trim to keep AFR on target. Is the intake Mazda original? Is the MAF clean?

 

Sorry maybe I confused you with the other pictures, the top one is the right one, it's 5.2 at idle with the rpm around 825. Those other two pictures were taken right after a fully warmed start up to show the fuel status thing I noticed on the torque app. It shows up right when you turn the key and goes away after a few seconds, that's probably why the reading is higher in those two. It does have the AEM/Mazdaspeed CAI. I have cleaned the MAF not too long ago like with 400 miles.