Hi all, first time poster and Acura owner. I understand this is a Honda forum but I'm aware the 3.5 liter V6 is also used in the Pilot. I'm not afraid to admit I have a Honda at the end of the day!! Damn proud of it lol 😆 After familiarizing myself with the cars features the last few days I decided to check out the diagnostic side of thing's on my MDX. What I noticed is at idle my long term fuel trims are in the negative. Bank 1 is between -2 to -4% and between -3 to 0% under load. My amateur knowledge leads me to believe that is pretty good. Bank 2 is a different story. Bank 2 at idle can go as high as -6.9% but once the car is driven and heats up the fuel trims calm down to around -2 to -3% and are close to bank 1. Under load around 45 mph bank 2 ltft will settle down to around -4 to -2%. Under 65+ mph conditions, bank 2 ltft will be in the -3 to -1.5% range. So far I've put 194 miles on her and after filling up my mileage is officially 17.1 mpg. This is 90% hilly driving with the AC on and a good amount of idling outside the garage learning the car's features also with the AC on as it's been thick and hot here in Pennsylvania. With the bank 2 numbers above, is this cause for concern? Maybe contact the dealer or will they say nothing's wrong due to not having any check engine light? The car has 14,000 miles on it and I was expecting damn near perfect fuel trims. Then again I'm used to fuel injected cars not direct injection. Or, am I being too critical and overthinking this? Funny, if I didn't have my obd fusion app running, I would have never known. The car runs great. Motor sounds good and I sniffed the exhaust and it smells perfect. Not a hint of unburnt fuel. My only complaint is the little bit of soot that direct injection causes on the back bumper. Thanks for reading my first post/rant here's the girl in all her glory. 2020 MDX with technology package.

 

Your trims are fine. No such thing as perfect trims that's why they trim.

 

Understanding fuel trim numbers help one to understand how the engine is running.
Engineers design things to have a margin of error because nothing is perfect.
The exhaust runs out to meet the up streamO2 sensor. That sensor is called the air to fuel ratio sensor.
It helps to determine how much fuel to add to the cylinders by adjusting the length of time the fuel injectors open and close.
When the sensors see too much fuel in the exhaust it trims it down by opening the fuel injectors for a shorter length of time.
The fuel air mixture is under constant adjustment to optimize the engine performance/emissions
And vicesa a versa. The tolerance for the fuel trims are under 10%
Long term fuel trim and short term fuel trims help to diagnose engine running issues.

So, as the grumpy old man says, your trims are fine.