Gemner

iTrader: (4)

For several years I have been running really rich, mostly when I expect the ECU is in open loop. I am talking about super rich, not normal for our cars which I know all about, Im talking about in the 10:1 and below range. A very long time ago before any of this I was WOT and felt the car really die out sort of like if you hit the rev limiter but it was in the middle of a gear, no CELs though, I always just dealt with it by tuning out a lot of fuel whenever possible and everything was cherry. Fast forward to today. I have all my tuning equipment out of the car, it still seems to run fine in closed loop, I get over 25 MPG mixed. Now that there is no tuning, the engine stumbles a lot more at lower RPM than before, including leaving stop signs and low RPM in higher gears again similar feeling to hitting rev limiter. Randomly getting P0300 and P0302 lately when that happens. I suspect the P0302 just happened to read once when it specifically detected cyl 2, but that the P0300 is more of the telling story. I expect it all might read back to that die off a long time ago and the fuel issue. This has been the same through 3 different ECUs (separate, definitely unrelated story) Any thoughts? Im pretty stumped. I would think if the fuel was overpressure that I would get a code from the fuel pressure sensor. I would think if an injector was sticking or a similar issue I would either get a code or have terrible gas mileage.

Recap:
Car stumbled once time a long time ago during WOT and has never come back without tuning

Super rich when not tuned

P0300 and P0302 randomly, runs and drives fine

Stumbles under load at low RPM, leading to P0300 and P0302

No codes thrown from the overfueling

Gemner

iTrader: (4)

haha, no thoughts even? Seems to get worse when the engine is hotter if that means anything

metalpiotr

iTrader: (1)

"I have all my tuning equipment out of the car"
Is your car back to stock then? There could be mods making you run rich.

Are you burning oil? (I recall hearing somewhere that burning oil could give you really low AFR readings)

Maybe all your symptoms are related... but maybe not.
First thing I would do would be to try to do something about that misfire. If your spark plugs are not old, I would replace the ignition coil for cylinder 2 (I think this would likely make the P0300 go away as well). Not sure what exactly you mean by "stumble"... but misfiring can make it stutter/hesitate.

Gemner

iTrader: (4)

Back to stock completely. Im burning minor amounts of oil, nothing special, a quart every 3000 miles maybe. When this all started several years ago there was no oil burn going on yet, engine was around 60,000 miles when it started and now around 150k.

I think the stumble is causing the misfire rather than the other way around. I can run it for several tanks of gas without throwing another code, but it will pop up any time I let the clutch out a bit to fast and the engine RPMs get real low, to me that suggests it is misfiring when low RPM load is too high. Im planning to pull the UIM at some point and check the rear plugs. I checked the fronts and adjusted the gap a couple months ago before the misfiring came up and for whatever reason one was gapped at .060, maybe I will find something similar on the rears but I kind of doubt it and even if that is the case it shouldnt explain the rich running since there were no changes to the plugs between when it was running fine and started running rich

NmexMAX

iTrader: (22)

I don't even run that bad with my 440's.

Gemner

iTrader: (4)

yeah, I lost my "copy" of the FSM so I cant go back and read it, but I assume there is a code that would show up for overpressure in the fuel rail? Thats about the only thing I can think of that would make it run super rich over the course of 3 different ECUs and having replaced both O2s at least once each.

Other options like incorrect translation of the O2 sensor readings, excessive injector pulsewidth, O2 sensor drift would/should change when the ECU and O2s are changed

edit: oh, forgot to mention. I can keep the AFR in check a little bit by running a bored out MAF (just under 3") but it still runs pretty rich in open loop, untuned on stock injectors.

Gemner

iTrader: (4)

Ok, I just downloaded an FSM (search FTW) and it looks like there would not be a code for high fuel pressure and from what I can tell there isnt even a fuel pressure sensor to start with since the only pressure testing method in the FSM is by actually testing the rail. I guess this will need to be my first step.

NmexMAX

iTrader: (22)

Seems about right, I don't ever remember reading a fault code for it, and rather only a procedure to test for it in certain situations, which is done at the rail.

But why would it be higher? Anything you did?

Gemner

iTrader: (4)

nope. pressure damper failure maybe? This happened a few years ago so I really dont know if its related or not, but I was WOT one time and in the middle of a gear the car kind of lost like 30% of the power and it never recovered from there. I never got a code that time and have only had easily traced and understood codes since then so nothing I believe to be a symptom of whatever happened. All I know is that the power NEVER came back after that experience without tuning and anytime Ive logged AFR untuned using a wideband the AFR was off the charts rich. Car runs great once the absurd amounts of fuel are tuned out but now that its all stock its bothering me.

Gemner

iTrader: (4)

After reading a bunch of garbage on a Murano forum and checking some items over, I am going to replace the front fuel damper (seems to be ticking or feeling like a tick more so than the rear) and go from there. If I get nothing from that I will probably replace the fuel pump. I did notice after it had sat for a bit and I pulled the fuel pump fuse to run the fuel out, the engine only ran for a second or two, much shorter than if I turned the key on first and then removed the fuse. This could be from a bad pressure regulator/check valve which should be part of replacing the fuel pump