Fuel trims disappeared when accelerating with slight stall/shift issue .

[North to Alaska]

This is a long story.
2016 Nissan NV passenger 5.6L
$$$ is a bit short and already spent $ on a battery (old and needed replacement), alternator, and a mechanic’s confirmation on alternator diagnosis. And changed out transmission fluid.
Mechanic also diagnosed MAF sensor as bad from his scanner. We watched voltage go up snd down rapidly. He dod not use a volt meter though. I have seen nothing from observation of g/s on my scanner to indicate a bad MAF.

Nothing seems to happen until after vehicle has been idling in parking lot with AC on for a while. Temperatures are not excessive (in the 70’s). Coolant temp stays at 190 but intake temp reaches over 130.
Battery voltage with alternator going only gets to 14 initially but I watch it slowly fall to about 13 on the scanner at obd2 and ecu while idling. Going to remember to bring my volt meter next time.

Symptoms are stalling in parking lot (after idling) slight stall/not shifting down when trying to pass etc. in fact the shifting issues happens long after most everything has cooled to normal under the hood and I’m on my way home. Turning AC off seems to help. In fact turning car off and leaving hood open for a few minutes seems to help.

New alternator and battery didn’t change voltage issues. Possibly new alternator is also bad?

Final symptom and this really has me perplexed. I was finally able to watch my fuel trims just as i was getting a slight stall/no down shift at highway speed. —- all fuel trims disappear/go to zero for a few seconds.
So now I’m worried it’s the ECU. But i am still thinking it’s an electrical issue and maybe the ECU is not getting enough power?

Appreciate any thoughts, especially if you have seen this issue with fuel trims disappearing for a few seconds.

 

[dumkid]

I had this happen on a Honda Civic that used a wideband afr sensor. The fuel trims would do exactly what the wideband sensor said to do instead of adjusting over time like narrow band 02 sensors. The wideband sensor went bad, and the result was surging and cutting out on acceleration, because the sensor would randomly read way too rich and the computer would cut fuel to the engine. Check your O2 sensor voltages/milliamps

 

[North to Alaska]

I had this happen on a Honda Civic that used a wideband afr sensor. The fuel trims would do exactly what the wideband sensor said to do instead of adjusting over time like narrow band 02 sensors. The wideband sensor went bad, and the result was surging and cutting out on acceleration, because the sensor would randomly read way too rich and the computer would cut fuel to the engine. Check your O2 sensor voltages/milliamps

One problem though. If I recall, the A/F sensors were working just fine when this happened. Strange if both A/F sensors went bad at the exact same time?

 

[GSCJR]

Try a thorough cleaning of the throttle body assembly, followed by an idle relearn procedure. Good luck!

 

[North to Alaska]

Try a thorough cleaning of the throttle body assembly, followed by an idle relearn procedure. Good luck!

Throttle body is perfectly clean. Never had a throttle body that clean. But thanks!

 

[North to Alaska]

Had a chance ro run it this morning for a three hour trip
No issues
Didn’t notice before but fuel trim goes to 0 every time I hit the gas anyway…with no issues.
However. The A/F voltage is consistently 2.25 ish which is apparently very rich. Hitting the gas doesn’t lower that voltage very much. Letting off the gas will send it up to about 3.5 (going lean and is appropriate)

I don’t see both A/F sensors going bad at the same time. Which leads me back to the MAF sensor..especially when it gets hot?

 

[North to Alaska]

Watching fuel trims go up and down while idling in short order

 

[dumkid]

Stuck injectors? Does the exhaust smell rich? Your stft on one bank is -20%, meaning the computer is pulling fuel, which means unmetered fuel is getting into the engine or your 02 sensors/maf/other sensors are reading wrong. You could try unplugging the 02 sensors, which will default to a base fuel map. If your problems go away with the 02 sensors unplugged then it's most likely the 02 sensors. You can do the same with other sensors, although some cars won't run if one or more sensors are unplugged.