VQ35DE surging / misfiring under load

[BubbaFL]

Hey guys! I need some help figuring out what's going on with my QX4.

It surges / misfires under heavy load, like when I'm accelerating at highway speed.

Here's a video of what's going on. Pressure on the accelerator is constant during the clip. It runs fine up to about 4k RPMS, then starts surging / missing.

https://youtu.be/iMrKSaAXyCM

I've already hooked up a computer - the only pending trouble code is P0138, an o2 sensor fault for sensor bank 1 sensor 2. This has been an intermittent issue for the better part of a decade, and never caused any driveability problems even when the sensor acts up enough to turn on the check engine light.

There are no other pending codes. Check engine light is not lit. Upstream O2 sensors are look good and are sending signals that look normal.

Spark plugs have about 30k on them, NGK laser double platinums.

It did something similar about a year ago, an hour into a long road trip. I suspected bad gas, topped off the tank, let it idle for a while, and the problem seemed to go away.

It started acting up today about 1/4 tank after filling up; I topped it off with 5 gallons of premium. Tough to say if that made it any better or not. The video above is after burning a quarter tank of gas from the last fill-up.

Anybody have ideas what might be going on?

With no codes, I don't want to start throwing parts at it.

[BubbaFL]

I should add: I can run it up to 5k+ RPM in neutral and it sounds fine. This problem only happens under load.

[macgiver]

mac ,if you never fix it at least you have a Rev-limiter @ 4K But see if fuel is restricted ,fuel pressure gauge on it and/or R & R filter - do the blow-test . Whichever is easier for you

[PathyPop]

Sounds like a marginal fuel pump to me. At 170k miles if you've never replaced the pump in the tank I'd start there as it's less than $100 including the fuel filter (as macgiver mentioned). Reving to 4k rpm under load is more likely to be starved for fuel than reving to 5k while parked. It's pretty easy as there is access under the rear seat and you don't need to drop the tank like so many newer cars. Although easy, safety first with gas tank open.

https://www.youtube.com/watch?v=TD0gz_-pB4I

[BubbaFL]

Went for a drive this morning, and the problem was gone.

Possibly related to heat buildup?

Got a fuel pressure test kit from Autozone, but it didn't have the right adapters so I couldn't check the fuel pressure.

I went ahead and changed the fuel filter (lot of brown crud came out of the old one), and the fuel pump. Gas in the tank looked good, and the inside of the tank was clean.

Guess I'll have to take it for another long drive on a hot day and see if the problem happens again.

[Wrierblock20]

My failing injector caused that issue only when warm.

[BubbaFL]

My failing injector caused that issue only when warm.

Did it throw any codes? If not, how did you figure out which injector was failing?