Bogging Under load, Upstream sensor code

Hi all,

this is my first time posting on here, and i really hope this is the last forum i have to result to in order to get to the end of this mystical issue i have been exploring on my V36 2007 G35x with the VQ35HR motor. Ive been chasing this issue for months now. I have an eBay axle back, as well as AAM resonated test pipes. Ive been getting an occasional P2A00 code (Bank 1 Sensor 1 out of range/performance, which I originally thought was a bad upstream sensor, which I then replaced both upstreams and continued to get the code. I then purchased an OBD2 bluetooth dongle and a tablet to use torque pro for data logging to figure out what is really going on here. From just the live data, I can tell something is off from STFT values. They seem to show the ECU dumping fuel into bank 1 (maxed out fuel from at 25%) and bank 2 seems normal. My first thought was vacuum leak, so I listened all around my engine bay with a tube jammed in my ear, and all I could find is a slight hissing near the PCV valve and line, which apparently can be normal, but i replaced the line anyways. I also tried spraying TB cleaner all around the engine bay several times. I also notice some bogging if im just cruising around like 30-40 mph, and then put my foot down as if to pass someone in traffic or make a yellow light, the car seems to not know what to do for a sec, rpms kind of jerk around, and then a half second later were accelerating as if nothing happened. Live data is showing me for that little Half second, the AFR leans out towards 15.5-16.0. Sometimes the car drives and idles completely normal, fuel trims look good and all, and other times not so much. Since ive gotten the car about 6 months ago though, fuel consumption has been absolutely horrible, around 200 miles per 20 gallon tank if im lucky (city driving though). I pulled spark plugs a month or so ago and found one plug missing the tip (electrode) and replaced all 6. I have attached a log where I had gotten to the end of a drive, and saw on my data logger that my bank 1 ST fuel trim was sitting steadily at 25%, Bank 2 ST is normal. The AFR was sitting around 13.5 (pretty rich compared to stoich) I started logging, let the car sit for about 30 seconds, killed the engine, then restarted the car. All while keeping the same log recording. Upon restart, fuel trims act normally again, and AFR sits at a comfortable 14.7. I hilighted the section where the car was OFF in red, so you can easily see where that happens on the excel file. Can anyone give me some insight onto what could be causing this? I can't figure out what condition was met in the first section, causing the high fuel trim, and what changed after restarting the car to deter the issue. I know when dealing with this, vacuum leaks are likely. However I question the vacuum leak due to the problem simply disappearing upon restart. Recently I cleaned and swapped MAFs between banks, as well as swapping coil packs, injectors, and examining spark plugs. Also replaced gaskets where test pipes mate to exhaust manifold, and where they mate to the Y pipe, no leaks whatsoever now. Nothing has led me anywhere. Also twice now, once while just sitting at idle for around 30 min and once after a pull from a dig, the idle started to uncontrollably climb to around 1.5k and i got codes for idle control failure, which also disappeared with a restart of the engine.

TL;DR
2007 G35x Sedan bogging under sudden acceleration, shows random high fuel trims on bank 1 and inconsistent AFR
Log file attached, would appreciate some insight interpreting the data

Link to excel file:

docs.google.com/spreadsheets/d/1Zpq0w7Pu...5&rtpof=true&sd=true

Would you be able to take another capture? The data you attached definitely shows a problem, but you can narrow your focus with a few changes.

You've got the Equivalence Ratio commanded and actual PIDs, but it'd be helpful to have the signal voltage PIDs as well. I'd also like to see the downstream O2 signal voltages, especially with the engine hot after a test drive, or while cruising down the road. The idea is make sure both the downstream and upstream sensors agree on the lean condition.

Loop status would be helpful as well. I don't recall what the Nissan OEM data equivalent PID is off the top of my head... :blush:

Can you take a capture during a WOT run? All the way from the end of 1st to the top of 2nd at wide open would be great. Do this safely and legally.

For whatever it's worth, I grabbed the detection logic for P2A00:



I attached that because it's been my experience that this code with this engine is very often an exhaust leak. I know you said there isn't one, just explaining my experience. That or a failed downstream sensor. That's why I'm interested in checking all four sensor during a drive. The downstream fuel control issue ends in a skewed A/F Adjust/Self-Learn value, and a false lean condition.

A quick/easy way to determine if you're fighting a false lean due to a downstream fuel control problem is to clear the Self-Learn values. If your scan tool will do that, great. If not, there's a manual method:



GST is Generic Scan Tool. Basically, it wants you to set a MAF code, then clear the codes and recheck.

If your lean condition disappears for awhile after doing the Self-Learn clear, then you're chasing a downstream problem. If it comes right back, then there's a genuine fuel control problem.

I know for a fact atleast one of my downstream sensors is bad. I’ve been getting codes for those for a while now but It was to my understanding that the downstream sensors simply babysit the catalytic converter efficiency and have no bearing on AFR. Is this the truth?

coolbro50.d wrote:

but It was to my understanding that the downstream sensors simply babysit the catalytic converter efficiency and have no bearing on AFR. Is this the truth?

In the case of your Infiniti, that's not the *whole* truth. The downstream sensor measures cat efficiency, sure. But that's not all. Nissan/Infiniti have been using a relatively aggressive downstream fuel control strategy for many years. Other OEM's have downstream fuel control, but don't allow them to have nearly as much influence.

If you happen to be a Premium member, Paul had similar struggles on a Sentra with an exhaust leak:

www.scannerdanner.com/scannerdanner-prem...ghlight=WyJwMmEwMCJd

I know for a fact atleast one of my downstream sensors is bad. I’ve been getting codes for those for a while now

Oh? Which faults were you getting, exactly?

I’ve been getting a Bank 2 Catalyst efficiency code, as well as heater control circuit, and high voltage.

I wasn’t too worried about the catalyst efficiency though, being that I don’t have cats.

Here's a link to a log I just took, tried to include extra pids. Started with car in on position after a drive to dropping someone off, started car, did a few WOT pulls, one from top of first like you said. I let the car sit for about a minute after the drive ended

Link: docs.google.com/spreadsheets/d/1pQN63_Gl...5&rtpof=true&sd=true

Love it, thank you! I'm pretty crap at Excel, but I was able to make this look decent:



You can see the difference in downstream behavior. B1S2 trends lean after the heaters get turned on around frame 550. B2S2 has a much wider amplitude.

The really fun part is after frame 850. Upstream on bank one indicates rich, but the downstream is lean. That can't be. :silly: Bank two is more rational. Check your fuel trims around the same time. Bank one total is about +30%. Bank two is -5%.

That's what I mean by a downstream fuel control problem - Bank one is getting overfueled in reaction to a downstream sensor issue. That's why exhaust leaks and failed downstream sensors matter on this system.

Wow, I appreciate you reading through all that data, and being able to put it into a concise chart. That makes sense regarding the data being skewed once the heaters turn on, being that I was searching for some condition that would suddenly cause the added fuel in bank 1. So you think by getting some solid downstream sensors in there, i could solve this relatively easily?

coolbro50.d wrote:

makes sense regarding the data being skewed once the heaters turn on, being that I was searching for some condition that would suddenly cause the added fuel in bank 1.

It's tricky, the way this system behaves. That's part of why I was suggesting the Self-Learn reset. This downstream fuel control correcting out to +30% isn't instantaneous, but learned over many miles. By doing the reset, you can temporarily make the problem go away, and confirm you're on the right track.

So you think by getting some solid downstream sensors in there, i could solve this relatively easily?

Possibly? The problem is that the sensor trending low suggests an exhaust leak between the upstream and downstream sensors. I know you say there isn't one, but if there is, then it won't matter how many sensors you throw at it.

One test you can do is to get the engine warmed up (like at the end of your last capture) and add carb clean/brake clean to the intake at idle. All four sensors (both AFR's, both O2's) should agree on a rich condition. This will check if the B1S2 is capable of reading full range or not.

Another test is to take a handful of rags and plug both tailpipes. Be careful and don't get burned, obviously. This will create backpressure in the exhaust and prevent any exhaust leaks from sucking in air. If B1S2 now shows rich, you're fighting an exhaust leak.

I don't mean to be rude when I say this, but with the cats removed like they are, is fixing the downstream issue worth it? :huh: I don't know how it goes with Nissan/Infiniti, but I'd think that an ECM tune of some kind could probably ditch the cat and the downstream monitors entirely. [EPA]FOR OFF ROAD USE, OF COURSE.[/EPA]

I’m going to perform the series of tests you indicated here. I also know for a fact that one of my downstream sensors is bad, and both of them were cheap aftermarket (i was under the assumption they do nothing except babysit cat efficiency), so i have two new OE sensors on the way. I agree about the tune info you mentioned, and a tune is something I want to get done in a few months once I have a few more mods, to avoid having to retune, being that a dyno tune at admin tuning for my car is around $1200 USD.

It’s crazy because the more i read into the downstream sensors, I can’t seem to find anything relating to how they could affect the AFR or trigger an upstream code. In fact, the only info I can find says that these sensors will not affect AFR., and if they were faulting, they would trigger their own codes. When reading the excel log, are you saying that the high fuel trims only begin once the heaters are turned on for the downstream sensors? If so, is that also when the upstream heaters are turned on? I have been also getting a B2S1 code along with the B1S1 code now, as well as B1S2 high voltage. I have two new downstreams coming tomorrow in the mail (like i said I know for a fact one of the downstreams is bad, i’ve been getting codes for it for a while now) and while i’m under there i’m going to feel around for exhaust leaks again, but i find it unlikely that there will be leaks due to the fact that i’m now getting the code on both banks, as well as that I just replaced gaskets at the exhaust manifold as well as where the Test pipes mate to the Y pipe.

Actually, i just found this thread:
www.nissanmurano.org/threads/p2a03-and-p...mance-issues.227151/
Post#3 is possibly exactly what’s going on.

coolbro50.d wrote:

It’s crazy because the more i read into the downstream sensors, I can’t seem to find anything relating to how they could affect the AFR or trigger an upstream code. In fact, the only info I can find says that these sensors will not affect AFR., and if they were faulting, they would trigger their own codes.

With respect to you and the reading you've done, but I'm not sure what else I can do to convince you. There IS a downstream fuel control system at work on your vehicle, and it's at least partly responsible for the issues you've having. I've done my best to demonstrate that.

I'm not ashamed to admit that I've had my ass kicked more than once by Nissan's and Infiniti's over problems just like this. Hell, I even drilled progressively bigger holes in my Sentra exhaust just so I could watch the problem happen. :silly:

When reading the excel log, are you saying that the high fuel trims only begin once the heaters are turned on for the downstream sensors? If so, is that also when the upstream heaters are turned on?

I'm saying the high fuel trims only begin once the ECM starts watching the downstream sensors as part of its control strategy. The ECM won't watch the downstream sensors until it heats them. Cold sensors don't read correctly.

The upstream and downstream sensor heaters have entirely separate strategies. Being the upstream sensors are wideband/AFR, their heaters get run nearly constantly to some degree or another. The downstream heaters only get run once the vehicle is driven down the road. Again, Nissan/Infiniti is somewhat unique in this behavior.

I have been also getting a B2S1 code along with the B1S1 code now, as well as B1S2 high voltage. I have two new downstreams coming tomorrow in the mail (like i said I know for a fact one of the downstreams is bad, i’ve been getting codes for it for a while now) and while i’m under there i’m going to feel around for exhaust leaks again, but i find it unlikely that there will be leaks due to the fact that i’m now getting the code on both banks, as well as that I just replaced gaskets at the exhaust manifold as well as where the Test pipes mate to the Y pipe.

Again, no offense meant, but that's why I suggested creating exhaust backpressure with rags in the tailpipe - To prove or disprove exhaust leaks without getting under the vehicle.

Believe me, i totally appreciate/trust the info you are giving me a ton. I just was finding it crazy how much conflicting opinion I could find online. You seem very knowledgeable on these cars and their systems, and if you were able to click that link I posted, i did find some supporting evidence on your side after some real digging. I’ll let you know the results of these tests/ the outcome of the new downstream sensors.

coolbro50.d wrote:

and if you were able to click that link I posted, i did find some supporting evidence on your side after some real digging.

I did, was glad to see that poster and I were thinking along the same lines. They're description of how this system works is fairly accurate, AFAIK.

I’ll let you know the results of these tests/ the outcome of the new downstream sensors.

Please do!

Also, what scan tool were you using for your captures? :huh: After playing with your data, I'm starting to see some value in being able to export data into Excel...

Update: before even getting into those tests you described, i installed two new NTK downstream sensors, and did the fuel trim reset by disconnecting B1 MAF, 2 days later, Afr and fuel trims seem normal. Both ST and LT values. No longer getting range/performance codes for either bank, and only get the occasional slow response for the upstreams, which i believe is due to them being aftermarket. I have two OEM sensors coming in for the upstreams which i plan to replace, and hopefully that solves the slow response.

I use a bluetooth obd adapter compatible with torque pro which is an android app i run on an android tablet which i velcro to my sun visor. I can view all live data PIDS in a custom interface and also data log. Works great and logging/outputting the data to excel is as easy and emailing the file from the tablet to my computer and opening the file. Thanks for the help! I’ll keep you posted if i see any more issues.

coolbro50.d wrote:

Update: before even getting into those tests you described, i installed two new NTK downstream sensors, and did the fuel trim reset by disconnecting B1 MAF, 2 days later, Afr and fuel trims seem normal. Both ST and LT values. No longer getting range/performance codes for either bank, and only get the occasional slow response for the upstreams, which i believe is due to them being aftermarket. I have two OEM sensors coming in for the upstreams which i plan to replace, and hopefully that solves the slow response.

Excellent. Glad to hear it! Did that also take care of the bogging/hesitation you mentioned?

I use a bluetooth obd adapter compatible with torque pro which is an android app i run on an android tablet which i velcro to my sun visor. I can view all live data PIDS in a custom interface and also data log. Works great and logging/outputting the data to excel is as easy and emailing the file from the tablet to my computer and opening the file.

Wow, I didn't know Torque Pro would data log that way. :huh: That's really frustrating, because I have Torque Pro but never could stand using it. Always got frustrated with the interface. Maybe I'll try it again.

Thanks for the help! I’ll keep you posted if i see any more issues.

Thank you! Following up with the fix is really valuable for other community members who might come through looking for help with their own vehicles.

Would you be willing to share another capture of a test drive with the new downstream sensors? I'd like to be able to make another graph like earlier with the after data for comparison.

The fuel trims are normal now, but the bogging/hesitation persists. I found some people online that claim it’s from running the test pipes and modified exhaust on the stock tune. What do you think.

Yes i can take another capture,
i’ll be back from vacation on wednesday, so i can take it then

coolbro50.d wrote:

The fuel trims are normal now, but the bogging/hesitation persists. I found some people online that claim it’s from running the test pipes and modified exhaust on the stock tune. What do you think.

I have a tough time seeing how the modified exhaust would result in a noticeable bog/hesitation? BUT, I don't play with 350Z's regularly, either. :silly:

Yes i can take another capture,
i’ll be back from vacation on wednesday, so i can take it then

Much appreciated! Please, don't feel obligated to respond on vacation.

I played with Torque Pro a bit today on my personal fleet. Saved a capture of a WOT run and... found the only thing I saved was some GPS data. :silly: How were you able to record variable valve timing PIDs? I found a Nissan expanded coverage plug-in, but it wouldn't let me install it because my version of Android was too new? :huh: