2006 Kia Sportage 2.7 V6 High Negative Fuel trim issues/Concerns

Hello all,

I was diagnosing this vehicle as customer complained of low power and gas consumption. As I drove it, did not noticed any loss of power as it would drive normal. I checked for codes and none in memory or pending. Then i looked at the fuel trims and noticed the long term being around -47 and short -13 on both banks. Also, when looking at O2 sensor it was around 12,000 mv, never seen anything within the range of fuel trims or O2. There was miss fire miscounts on cyl 1 (2500) and 6 (30,000) approximately . The vehicle has approximately 50,000 original miles or less as it belongs to an elder woman who hardly drove it and she has been the original owner. I personally known her.
Not sure if the MAF on this vehicle is cleanable or not, does anyone know what range this sensor should be on this vehicle? Also, has anyone ever seen something within these ranges on fuel trims and O2? I’m thinking of leaking fuel injectors to have the misfire counts on both banks. The spark plugs were replaced last summer maybe 5000 - 10,000 miles ago with Kia OEM.
Does anyone know how to test the fuel pressure on this vehicle? Don’t see a shader valve or a place to connect to, perhaps does anyone would know how to check for leaking fuel injectors on this vehicle? If you have Mitchell or all data and could send me some information would greatly appreciate it.
Let me know your thoughts or inputs to this. Not wanting to make her spend money on injectors and MAF for nothing.

See page 7 of pdf "ecm terminals" there's ~15,000mV dc bias on the o2 grounds, maybe that's what you were reading.

I didn’t receive your pdf attachment.

There's three boxes below my post, hover over those perhaps ?

are the rear o2s reading the same thing , see if the heater might have blown fuse it's taking all the fule away

Also a stuck open Thermostat will cause a rich condition