I hate to ask this question, because I have researched this endlessly, but I am ready to push my car off a cliff if I can't figure it out. I have taken my 2008 G37s (manual) to both the dealership and a shop that specializes in Nissans/Infiniti. The dealer only did the basics and the indie shop helped, but was honest about how it could be almost anything and I would be spending more money hunting the issue down than the car may be worth (sarcastically). The indie shop did confirm that this was not an issue of my timing gasket being blown, which was nice to hear.
I have spent countless hours climbing under the car and on top hunting vacuum leaks (even tried the smoke machine method!). I am not seeing any cracks in the manifold. PCV valves have a little oil on them, but nothing that seemed abnormal. I only found a tiny drop of oil down a few of the spark plug 'holes'. I do not believe there is a leak there. The fuel pump and filter were pulled from the tank and verified working just fine. The only thing I have not done yet is pull the RHFC's to see if they may have cracked near the upper flange. I have swapped the AF/O2 sensors from side to side to see if the misfires followed, but they remain on Bank 1. I have swapped the MAF's as well with the same results. Aside from a possible bad BCM, I am at a loss here. Does anyone have an idea of something else I can try? I have attached a recent diagnostic report. You can see that the short term fuel ratio for bank 1 is way too low. Any help is greatly appreciated!

Issue: The dreaded P0300 code. Limited to cylinders 1, 3, 5 (bank 1).
Replaced so far:
-spark plugs (dealer installed)
-coil packs (6)
-plenum seal (dealer installed)
-battery
-MAF's - both
-cats replaced with FI RHFC (less than 5k miles)
-AF sensors (Denso)
-O2 sensors (Denso)
-Fuel injectors (Denso)
-Fuel injector subharness (OEM)
-VVT solenoids - both
-PCV hoses
-multiple throttle/ecu relearns
-intake tubes (oem - both were torn)
-possibly other things I can't remember. Been working on this for a year.

 

more diagnostic reports stuff...

 

Has the fuel pressure been measured? Our engines require a special tool (fuel tap) in order to do this.
(here is the one I use: https://cj-motorsports.com/products/fuel-tap-npt-2-bolt)
The factory spec is ~51 psi at idle.

As for the "-15% short term fuel trim" keep in mind that you can't just look at part of the fuel trim.
To get the total fuel trim, the short term and long term fuel trims must be added.

Your bank 1: -14.06 + 0 = -14.06%
and bank 2: 3.12 + 0 = 3.12%

The factory shop manual states that the allowable difference is between -15 to +15%
So your fuel trim is in the OK range.

Can you provide the full diagnostic report with the engine fully warmed up when at idle?

Also, use OBDFusion (or OBDLink) to data log the:
• O2 sensor lambda (Bank 1 Sensor 1)
• O2 sensor lambda (Bank 2 Sensor 1)
• O2 voltage (Bank 1 Sensor 2) (V)
• O2 voltage (Bank 2 Sensor 2) (V)
• Mass air flow sensor A (g/s)
• Mass air flow sensor B (g/s)
• Engine Rpm

Then in a second log:
• Short term fuel % trim - Bank 1 (%)
• Long term fuel % trim - Bank 1 (%)
• Short term fuel % trim - Bank 2 (%)
• Long term fuel % trim - Bank 2 (%)
• Engine RPM
• Absolute Engine Load

When data logging, we want to capture different states of the fuel system:
• Let the car idle for 1-2 minutes
• Drive 30-50 MPH at a steady speed (use the cruise control if you want) for 1-2 minutes
• If possible, try to get a few wide open throttle runs in second gear.

 

Thanks for taking the time to look at my issue. I am not 100% sure if the indie shop checked the fuel pressure. I'd honestly wager that they did not. All they mentioned was removing the fuel pump, checking that and making sure the filter wasn't too dirty. I'll try again at getting those specific data logs tomorrow when I can get an extra set of hands to run the app while I drive.

Much appreciated.

 

Well its been quite a while since I messed with the car. Covid kinda put a damper on driving it or really worrying about the issue. I finally got the wife to go out with me this last weekend to pull some numbers (attached). I tried to run the reports that SonicVQ suggested but I was limited to only 4 sensors at a time with my version of OBD Fusion, so I had to make 4 different drive logs. All were done on the same 45 MPH stretch of road and all started with roughly a minute or so of idle time. When looking at the logs, anything close to 1k RPM is idling. I have also added the most recent diagnostic report taken right before we started. Hopefully someone with more knowledge can help decipher this for me. Any help is greatly appreciated!

One thing I noticed is that the scanner didn't pick up the MAF 1 & 2 readings. I'm wondering if that may be the issue now. Although it was able to read the Mass air flow rate on all the logs. I know I've already replaced those on both sides, but its always possible they were crap from the get go.

Thanks in advance!

 

Older versions of OBD Fusion didn't show MAF A / MAF B, please check to make sure you are at the latest version: Settings > About > Information
(Current version is iOS: 5.10.0.1194, Android: 5.10.0)

If you are at the latest version, then maybe the early G37 ECUs don't provide that data to the OBD system. The 2010+ G37 do provide the MAF A/B data.

Observations from the (awesome!) data you provided:
(1) Your misfire counters are VERY high on cylinders 1,3,5... and they are all on bank 1, which is the passenger side of the engine.

(2) Fuel correction aka "Fuel Trims" To get the total fuel trim/correction, we need to add short term + long term for each bank: In y our case bank 1: -29% and bank 2: -11%
A total fuel trim of -15 to +15 is acceptable according to Nissan/Infiniti.
Here we have another item pointing to bank 1

(3) Your rear O2 sensor voltage is showing both banks being lean (lower voltage) and bank 1 is slightly leaner... now three items are pointing to bank 1
Normal rear or sensor values should swing between around 0.1 volts to about 0.9 volts.



Here is an excellent video showing the typical rear O2 sensor voltage swings on a G37:

Next Steps:
VERY carefully examine every tube, hose, clamp on bank 1 / passenger side of the engine.
Either extra air is getting into the engine, bank 1 MAF is over under reporting air flow,
-or- there is a plugged fuel injector on bank 1. (possible, but not likely)

Try This:
swap MAFs, drive for a few days, run the diag report at hot idle and data log again.
If the lean condition switches sides, we know it is the MAF.

 

Thank you for the very quick and detailed response! I am using the latest version of the app (5.10), so its probably just my car.

I've replaced the air intake tube on that side, but I will check for any leaks again. I should also check the airbox for cracks or something. The car was never wrecked or anything, but it is a 12 year old car. I've ruled out the injectors because I have already replaced them (denso) and even swapped sides to see if the lean moved to Bank 2. No changes there. I did the same with the O2 sensors a while back in an attempt to get the issue to move sides, but nothing there either. So I guess this may rule out the MAF. Next step will be to check for leaks. Do you think I can use a fog machine in the tailpipes without damaging the O2 sensors? I've used that trick to locate leaks on old cars before but nothing with O2s. At this point I'm afraid that the FI RHFC's may have a leak. I did add those a few hundred miles before the issue started.

Thanks again for all the insight! I will get the car lifted again and get to work checking for leaks.

 

I graphed AFR (Lambda) against rear O2 sensor voltage and I am 90% sure the issue is the FI HFC not functioning properly or there is a crack in that area.

In "Drive 1" when you accelerated, lambda went rich to around 0.70 (~10.2:1 AFR), BUT the O2 sensor voltage only got up to 0.7 volts, when it should be around 0.9 volts.

 

Much appreciated SonicVQ! I owe you a beer or something. Over the weekend I went ahead and pulled the RHFC and what do I see? Is that a leak? Yes it is. I had a few of the Z1 metal gaskets handy so I swapped those out and tightened it back down. This made the exhaust leak worse and much more audible. These are much thinner than what was on there previously. I can't remember if I was using OEM or the FI gaskets when I installed the cats, so I went ahead and ordered some thick gaskets from Concept Z Performance to replace these. Then I pulled the RHFC again. While it was out I checked the 3-bolt flange for straightness. I don't have a pic, but there was a pretty significant curve in the flange where you see the gray discoloration (shown in the image below). Enough of a gap to slide folded card stock under. I am pretty sure this is what caused my leak. I will mill the flange back to being perfectly straight, replace the gaskets and try again.

I will update this with my results once I get the new gaskets installed. I'm not sure when that will be. It seems like CZP is running a little behind when it comes to processing orders at the moment.



leak visible up top here


Z1 gaskets that leaked pretty bad (in my case)

 

I have to say, thats some very thorough troubleshooting.

Would love to take the car off your hands, but my wife's patio renovation has crushed my budget.

 

Subscribed!

 

I have been troubleshooting this error for the past 6 months. i have replaced coils, plugs twice, cleaned everything, replaced vacuum hoses, O2 sensors, Air/Fuel Sensors, replaced valve cover seals (due to leaking oil into injectors), and i am still getting this error. I have a performance R2C intake, running a test pipe instead of a CAT, and have a full free flowing 2.25" exhaust. I noticed you replaced gaskets on the downpipe if i am seeing that correct. i know that i have a small exhaust leak from the gaskets on the test pipe, did that solve your problem? I am ready to run this thing into a wall just to get the engine light to turn off. It runs strong for about a day or 2, then the POS light comes on, idles like **** and has a loss of power until i reset the computer, then i am good for a day or so...

 

Did this fix it?

 

In all honesty, I have only driven the car maybe 5-10 miles since I changed out the gasket (I rarely drive the car). I still have a pending misfire code after the change but this may also be due to the (possibly) faulty O2 sensor that SonicVQ mentioned last. I do have a replacement that I expect I'll throw on this weekend and try it again. I'm not 100% certain our issues are the same though. I have never had a loss of power or rough idle while the code was present. In reality the car drives just like it always did but idles at about 1k instead of being closer to 700.

If you are going into limp mode, might I suggest looking at the VVT solenoids. At least use a tester to check that one isn't faulty or has a bad connection. From what I read a while back, that can cause rough idle, misfire codes, etc.

 

The rough idle only happens after the misfire codes come back. The car goes into safe mode from the code, which is why it issues at 1000. It normally idles around 6500 when there is no check engine light from the misfire codes. I will take a look at the VVT solonoids. No clue what those are or what they do, or how to test them.

Thanks!