I posted this over on the Path but hoping to get some responses.
Looking for opinions while troubleshooting an issue with my pathfinder.
The car has been running fine. There is a check engine light on for bank 2 CAT which has been on for about a month.
The other day I filled the tank with regular 87 octane fuel which I sometimes do.
Shortly after leaving the fueling station, while climbing a steep hill the engine started cutting out losing power.
The engine never shut off and I was able to make the top of the hill. I turned around headed back home under reduced power.
The car starts and idles fine. It loses power under acceleration.
My first instinct was bad fuel. I checked with the station and the manager said he had no other complaints.
I disconnected the fuel line from the rail and filled up a clear glass with the fuel and let it set. No separation.
I plumbed a pressure gauge between the fuel line and the rail and I get a steady 50 lbs. pressure at idle.
When I power brake the car in drive the pressure drops off to 40 lbs at about 3k rpm.
I added a bottle of octane booster to the tank and took it for a ride. It runs a little better but still lacks power.
Still not throwing any codes other than the cat.
Thinking it might be a fuel pump, fuel filter or cam sensor issue?
I have a scan tool with a live data feature. Anything I should be looking for?
Any ideas? Thanks in advance.

Curious thing that would choke your power but not throw a DTC code, other than than cat code. It seems your driver side cat trouble code may be your first clue. What is the specific DTC for that flagged cat issue?

The 50psi at idle is right on target for your fuel pressure. When you turn off the engine, does the pressure hold steady, only slowly dropping off in a few minutes, or does the pressure drop off immediately?

Your scan tool data should be very helpful. What is the STFT and LTFT percentages indicated for banks 1 and 2 at idle and when the engine speed is held at 2500rpm for 10 seconds or so?

Thank you for the response.
The cat DTC is P030. It's been on for a while and the car ran fine.
STFT 1 idle 11.7 to 12.7
STFT 2 idle 14.8
STFT 1 @ 2500 rpm 8.6
STFT 2 @ 2500 rpm 9.4
No LTFT reading because I had the battery disconnected (guessing)

The pressure drops slowly when shut off.
Also, I taped the pressure gauge to the windshield and went for a spin.
Pressure was at 50 and only dropped to 48 under heavy acceleration. Could have lost that much through plumbing.
The motor missed so badly under load that it threw a multi random misfire code which cleared itself once back to idle.

Mr. Callaway wrote: ↑

Thu Dec 28, 2023 1:54 pm

The cat DTC is P030.
No LHTF reading because I had the battery disconnected (guessing)
The pressure drops slowly when shut off.

I assume you meant P0430.

Long term fuel trim is a learned setting that is continuously adjusted every 10 seconds or so. It will reset to zero if the battery had been disconnected but it should have self-adjusted within seconds after the engine reached normal operating temperatures and was then running in closed loop mode. Your scanner should indicate CL in the live data if it is in closed-loop. If it fails to get into closed-loop mode, there are a number of sensor failures that could be causing your ECM to not get the correct feedback, which includes O2 or A/F sensors, MAF sensor, air intake temp sensor as well as the ECT sensor. These sensor data are also indicated in the live data stream on your scanner and should be checked to see if they are all reading normal ranges.

After turning the engine off, does the fuel pressure drop slowly within seconds or minutes? How low does it go and how long does it take to drop to this lower pressure reading?

Those STFT readings are a bit on the high side or normal but can't be judged until the ECM wakes up in closed-loop mode to do its job.

If I was to make a guess at this point, without anymore data, I would suspect your MAF sensor signal voltage reading might be too high. A dirty MAF sensor will have contaminants insulating it, making it react like freezing cold air is flowing through your intake, which is higher density air that would require more fuel to keep the air/fuel mixture in balance. That could account for the higher than normal STFT and the random misfires as well as the catalytic system not operating within spec because there is too much unburned fuel continuously being exhausted. This is just my best guess at this point.

Thanks again:
The fuel pressure drops very slowly. Seems like minutes vs seconds.
I actually took the maf sensor off and sprayed it with some maf sensor cleaner.
Didn't clear the problem.
Earlier when driving around I did observe the CL readings in the live data.
Tomorrow I'll clean the maf sensor again and hope for better results.
Is it possible that the fuel I purchased was just too low of an octane?

Mr. Callaway wrote: ↑

Thu Dec 28, 2023 4:34 pm

Is it possible that the fuel I purchased was just too low of an octane?

Low octane fuel, like 87 which I use occasionally, will never cause the loss of power and misfires like you are seeing. Now that you do see the engine goes into CL, check the LTFT. If the LTFT and STFT are both at around 10% or higher, there is an issue, a reason, why more fuel than normal is being called for by the ECM. Possible vacuum hose leak (unmetered air being seen by the A/F sensors but not the MAF) or the upstream A/F sensors are getting worn out and slow to respond when more power is called for accelerating or driving uphill. So many sensors to test and so many possibilities. I sometimes feel lost without my hands on it and reading through the Nissan service manual for clearer direction.

Thank you so much for your input.
Why did you ask if the pressure dropped slowly or rapidly?
What is the normal condition for the pressure to drop after shutting off the engine?
Seems like it's taking a long time for the pressure to drop.

Mr. Callaway wrote: ↑

Fri Dec 29, 2023 5:49 am

Seems like it's taking a long time for the pressure to drop.

That's a good thing. Pressure in the fuel lines should hold steady when the power is off, only dropping off a bit (perhaps 1psi/5min) because the fuel pressure is trapped at one end by the fuel pressure regulator and fuel injectors and at the other end by a check valve. When pressure drops off quickly, that is a sure indication of a fuel leak through either the check valve, regulator, or injectors and that further testing would be needed to isolate the source of the leak.

Well, at least one thing is working correctly.
Thanks again.

Mr. Callaway wrote: ↑

Thu Dec 28, 2023 8:57 am

I plumbed a pressure gauge between the fuel line and the rail and I get a steady 50 lbs. pressure at idle.
When I power brake the car in drive the pressure drops off to 40 lbs at about 3k rpm.
I added a bottle of octane booster to the tank and took it for a ride. It runs a little better but still lacks power.
Still not throwing any codes other than the cat.
Thinking it might be a fuel pump, fuel filter or cam sensor issue?

I was scratching my head, wondering about this 10psi drop in pressure that just wasn't registering with me. After reading through the fuel system section of the FSM for your '12 model, I realized the fuel filter and fuel pump in R51 models are integrated into a single in-tank assembly, just like my Kia Soul. This is one of the worst automotive engineering ideas since the Ford Edsel. With my Soul, I can at least remove the assembly from the top of the tank, through an access hole in the floor, under my rear seat. Instructions for the R51, indicate the fuel tank has to be dropped to replace the pump/filter assembly. My Kia filter module can be replaced in the pump assembly but the Nissan R51 does not have that option. If the R51 filter is clogged, a new filter/pump assembly he needed.

After more than 10 years and (I'm guessing) more than 100k miles, I can safely say your fuel filter is clogged. The fuel pressure should not drop 10psi like it did unless there is a leak or the flow is being restricted relative to the demand for more power. You were likely right all along, thinking it might be the fuel pump or fuel filter. Unfortunately, a simple filter has to come with a costly pump and quite a bit more labor than should be reasonable for this otherwise routine maintenance item.

I bought my Kia Soul used, with over 50k miles on it. At about 56k miles I changed the fuel filter and cut open the old one for a look at the filter media contamination. The filter module and media are similar to the Nissan in-tank filters. Here is a side-by-side view of the new and used filters and the used filter with the end cut off. I have since then changed the filter once more at about 87k miles. The filter was again almost as blackened with contamination as seen in these pictures.

My Pathfinder has 157K mi. With that kind of mileage it could very well be a fuel filter, pump, regulator etc.
When I first tested the fuel pressure it was raining heavily and I couldn't adhere the gauge to the windshield. I ended up power breaking the car and it looked like it dropped 10 lbs of pressure but I was looking through a rain soaked windshield.
I ran the test again after the skies cleared and I taped the gauge to my windshield and took a ride. I had 50 lbs. of pressure at idle and it only dropped to 48 lbs. of pressure under load.
Some more head scratching information: My LTFT readings for both 1 & 2 don't move off of zero whether at idle or load, cl or ol no difference.
My mass air flow reading is .01 at idle and .06 at load. Supposed to be 6 and 20.
I replaced the MAF sensor with a new Hitachi sensor and no change in readings no change in symptoms.
I checked the wiring to the sensor and I have a good ground and get 12.33V on the pink wire and 4.775V on the brown wire. I think I'm supposed to have 5V on the brown wire but not sure if 1/4V will make a difference?
At this point I don't know if my scan tool is bad or I got a bad sensor?
Confused by the zero LTFT readings as well.
Could still very well be a fuel related issue. I'll run another pressure test tomorrow and see what I get.
Thanks so much for your input. Very much appreciate it.

One more note (or rant) on this design concept which is a self-destructive, built-in obsolescence type of design. At 100k miles, more or less, the fuel pump will be working overtime to keep up with the fuel pressure demands, as the filter clogs up and restricts flow, until the fuel pump fails or the filter clogs completely, which ever comes first. The design also wreaks havoc on the fuel injectors as the heavily loaded filter contaminants are slowly dissolved with detergent gasolines or fuel additives (Ironically, fuel system cleaners most often) until the injectors are then clogged.

Mr. Callaway wrote: ↑

Fri Dec 29, 2023 4:15 pm

Confused by the zero LTFT readings as well.

Me too.

Mr. Callaway wrote: ↑

Thu Dec 28, 2023 1:54 pm

STFT 1 idle 11.7 to 12.7
STFT 2 idle 14.8
STFT 1 @ 2500 rpm 8.6
STFT 2 @ 2500 rpm 9.4
No LTFT reading because I had the battery disconnected (guessing)

I forgot to mention the reason why I asked you to look at fuel trims at idle and at 2500rpm. The normal STFT response is an increase to higher engine speeds. The decrease you see is not normal and indicates a possible vacuum leak. As I mentioned, the STFT is a bit high, indicating a lean condition that your ECM is correcting by adding more fuel. At idle, when air flow is minimal and vacuum is high, a small vacuum leak will have a greater effect to the air/fuel mix ratio than when the engine is running at a higher rpm where the air flow is increased and vacuum is lower. When an engine runs faster or under increased load, more fuel is needed, not less.

I am always hopeful that a single source for an issue can be pin-pointed to correct what is ailing me, but enough about my bad back. I think there may be more than one contributing factor to the issues affecting your ride. Testing components in CAN bus systems, like in these R51 models, is more of a challenge to my old-school ways than I would like to admit.