Loss of power in 4low going up steep hill

[Erichimedes]

I've posted a few other topics here about our new 2012 Pathy, thanks for the help with everything so far. Now I have a new one that is puzzling me.

2012 Pathfinder, 140k, V6, Automatic, 4WD

This weekend we finally gave it a proper shakedown drive, over the Hurricane pass loop near Silverton, CO. Car did great, pretty much no issues except for one thing. It was in 4 low, 1st gear. On the last (very) steep climb over California pass, what I am guessing was the steepest hill of the day, the engine just completely lost power. I was probably around 3k-3.2k rpms, and it just instantly dropped to around 1500. The engine didn't stutter, or feel like it was going to die, it just felt like the car was deciding to drop the power for reasons of it's own. It felt like my wife's Jetta when traction control feels the wheels slip and just kills power to the engine. Traction control was off (or the dash light said so anyway) and no dash lights came on during this incident.

It did this probably 3 more times while I tried to get to the top of that section of trail, including a weird lurching hop for a couple seconds while I tried to just make it go. Eventually I tried proceeding at a lower rpm, and kept it around 2.2k-2.5k and it did not do it again. The rest of the day was completely uneventful.

Scared the hell out of me, with my whole family in the car. This is the kind of driving we bought the vehicle for, so I need to figure out what the problem was. I've done some internet searching and can't find much on this issue. This was around 12,600 feet, so I'm sure the engine was struggling a little, but it didn't have any issue at all starting from a full stop on the steepest trail of the day.

Any insight is very appreciated, TIA

[palmerwmd]

12600 feet is a lot of altitude for a non turbo engine.
Having said that, a loose sensor connection or a sensor going out comes to mind.
Like a camshaft postions sensors.
Yours are probably about due anyway.

I had them go out on my V6 NIssan Xterra (identical powertrain to yours except for driveshaft lenght) and the first couple times symptoms were broadly smilar.
Also no codes at first just abrupt loss of power on a hill.
Got progressivly worse.
The good news is , even the highest quality ones you can buy ( hitachi) do not cost all that much, if you buy them online.
And if u are handy you might try to put them in yourself.

But if this is what I suspect it will happen again a couple times and then trhow a Camshaft position sensor code.
crankshaft position sensor is also possible.

[TooMuchControl]

get a OBD code reader, and see if "pending" codes are stored there, next time, this occurs.

[Erichimedes]

Interesting, I've never heard of turbocharged engines doing well at altitude, maybe the newer ones do? Around here people avoid turbos because they generally do more poorly than NA when you get up high. But maybe that's an outdated way of thinking, I don't know.

Good thought about the cam position sensors, I'll put that on my list of things to look at and/or replace.

I actually have an OBD reader, but it wasn't with me. It's packed in the car now. I checked it just a minute ago and no pending codes.

I've been doing more reading about TCS in these trucks and it sounds like even when it's "off" it's not actually fully off. When the dash light says off, the sensitivity is just turned down, but it will still kick on if all 4 wheels break loose. This sort of makes the most sense to me, just based on how it felt, it felt very controlled. It still has the old tires on it, which are not in bad shape but they're only highway tires and I'd almost be shocked if they hadn't broken loose on that section where I had the issues.

[TooMuchControl]

In reading some information from our friends at Frontier forums, it appears that some programming changes were made after the '09 model year in relation to throttle position / rpm / speed.

There is some sort of open throttle / speed limiter programmed in that may cause something like this. Some have solved it by tuning.

You could have been at wide open throttle even at 3k rpm under altitude conditions, and the engine may have been smart enough to back off the throttle to optimize power before something more alarming would have occurred.

It would be great to see what all the air/fuel sensors are trying to do at that elevation.

I don't want to start you down my uneducated path on this, but I dive into the Xterra and Frontier forums as they have the same engines periodically and they may have information relative.