I've discovered an AFR sensor problem in my Fortuner, that explains why for so long I've felt the car getting sluggish when driving for a while in the extreme heat.
A couple months ago I had done very precise fine-tuning on closed-loop operation, to get it just right. After I felt very satisfied, and got most closed-loop AFR above 12:1 AFR, I went on a road-trip. While going on the trip this is what showed up in my AFR gauge:
I was shocked, why is it getting so rich? I just finished getting closed loop done properly? So I thought there must be something wrong. I pulled out my OBDII scanner, started up my tablet, and got connected to my ECU, to find this:
My right bank sensor was giving a wrong reading, and the right bank fuel trims are going haywire. Left bank is doing ok. So I knew this is either a bad AFR calibrator, a bad AFR sensor, or a bad harness. This problem only appears after driving for a while in the hot weather. Doesn't appear in the winter.
When I got home, I swapped the yellow and blue wires in the AFR calibrator to see if the problem moves to the other side. It didn't, which clears the calibrator from any faults. So now it is down to the right-hand-side sensor or the harness. I replaced the right sensor with one old sensor I had in my stash, and I have not tested the car yet. If the sensor turns out to be cleared, then it is down to the harness, which is what I am suspecting.
The harness I have was a used one I bought a couple of years ago when I was trying to get the UCON EMS working, and after installing it found that the right hand sensor wires were cut and then reattached by twisting them together, without crimping or soldiering. So I fixed that by soldering them properly a couple of years ago. I think the soldiering that was done is causing some current to escape some how, causing the AFR reading to get thrown off, when the heat is cranked up and the wires/soldering expand. Some how. This explains the high heat sluggishness, when the right bank goes down to 10.5-11:1 AFR at partial throttle, the engine will definitely lose a lot of power. Now whenever I start feeling it getting sluggish, I look down to the AFR gauge and find that the problem is happening again.
I am now certain my car was built by Murphy.