P0171...nothing seems to fix it for me.

[IlyaK]

So...let's start off this thread with a bit of history.

In July of 2007....I got SS AutoChrome Headers and Y-Pipe, Magnaflow High-Flow Cat, Budget B-Pipe, and a new OEM 4th Gen. Muffler. I also got an O2 Simulator since I was going from being Cali. Spec. to Fed. Spec.

Soon after it seems, I got a ghost code for being lean on bank 1 (P0171).

In the winter of 07...I switched from the SS AutoChrome Y-Pipe to a stock OEM Fed. Spec. Y-Pipe due to noise. I wanted something quieter. Still, the code was ghost.

About 1 month ago...I installed a Apexi VAFC-II because I was planning to 00VI/MEVI VERY soon. Since then, the P0171 code has been lighting the CEL (no longer ghost). I had the VAFC-II doing NOTHING...so I don't know why it would all of a sudden trigger that code to become an actual CEL. But anyway...2 weeks later I got an 00VI.

I had some major problems with the 00VI install. I ended up having a cold start (which I have fixed by adjusting the idle). I also had a vacuum leak and a rear valve cover leak. I fixed the rear valve cover friday night with a brand new gasket from Nissan...although with new cover grommets and bolts. I also found the vacuum leak and took care of that.

At the same time that I had the issues above...I also developed a P1105 (MAP/BARO Sensor Fault) code. I fixed that by getting another used "boost sensor" (located on the intake snorkel of a 4th Gen.)

Now...I've done a LOAD of searching on this P0171 code, both on here and google in general. Most links and threads led to it being a MAF problem. Now, I have three MAF's...one of which throws a MAF Circuit A Failure code. What is the probability of the other two being bad?

Right now I only have a P0171 CEL and a P0171 Pending CEL.

Here is what I've done (cliff's notes):

• Tried all three MAF's
• Replaced RH O2 Sensor (the one located in the back near the IM)
• Replaced Boost Sensor
• Replaced Knock Sensor during 00VI install
• Fixed any leak I could find...spraying the engine bay with TB cleaner trying to find any other possible leaks
• Replaced PCV Vavle
• Replace Rear Valve Cover Gasket (suggested and needed)

I do have an exhaust leak somewhere under the car it sounds like (Y-Pipe flex section perhaps?). Would this cause a lean code CEL? I have the Apexi tuned a little bit....do I need to go get an A/F Dyno and tune it better? The guy who tuned it had the values for a similar setup written down in a notebook.

All of my maintenance is up to par. I'm anal about maintenance.

I NEED HELP. My inspection ends at the end of this month and I've spent about $275 and 3 weeks of time trying to combat this myself. I do not want to spend $300 on a new MAF sensor either. Could it be my O2 sim? I have another new that I never used cause I thought my other one died (light wasn't blinking but it's been fine for like 8 months since)...but if the sensors controlled by it were bad...I'd be getting a P0172 (bank 2 lean). Is it a result of my cheap EBay ram air intake? I'm getting a 5th Gen. complete intake that I'll be installing as soon as I get.

SOMEONE HELP ME. PLEASE!

Here is how the bay looks right now:

[IlyaK]

Anyone? I need help in a major way. My inspection is up at the end of the week...

I typically wouldn't bump something like this...but I need help.

[altezzablazes]

Originally Posted by IlyaK

So...let's start off this thread with a bit of history.

In July of 2007....I got SS AutoChrome Headers and Y-Pipe, Magnaflow High-Flow Cat, Budget B-Pipe, and a new OEM 4th Gen. Muffler. I also got an O2 Simulator since I was going from being Cali. Spec. to Fed. Spec.

Soon after it seems, I got a ghost code for being lean on bank 1 (P0171).

In the winter of 07...I switched from the SS AutoChrome Y-Pipe to a stock OEM Fed. Spec. Y-Pipe due to noise. I wanted something quieter. Still, the code was ghost.

About 1 month ago...I installed a Apexi VAFC-II because I was planning to 00VI/MEVI VERY soon. Since then, the P0171 code has been lighting the CEL (no longer ghost). I had the VAFC-II doing NOTHING...so I don't know why it would all of a sudden trigger that code to become an actual CEL. But anyway...2 weeks later I got an 00VI.

I had some major problems with the 00VI install. I ended up having a cold start (which I have fixed by adjusting the idle). I also had a vacuum leak and a rear valve cover leak. I fixed the rear valve cover friday night with a brand new gasket from Nissan...although with new cover grommets and bolts. I also found the vacuum leak and took care of that.

At the same time that I had the issues above...I also developed a P1105 (MAP/BARO Sensor Fault) code. I fixed that by getting another used "boost sensor" (located on the intake snorkel of a 4th Gen.)

Now...I've done a LOAD of searching on this P0171 code, both on here and google in general. Most links and threads led to it being a MAF problem. Now, I have three MAF's...one of which throws a MAF Circuit A Failure code. What is the probability of the other two being bad?

Right now I only have a P0171 CEL and a P0171 Pending CEL.

Here is what I've done (cliff's notes):

• Tried all three MAF's
• Replaced RH O2 Sensor (the one located in the back near the IM)
• Replaced Boost Sensor
• Fixed any leak I could find...spraying the engine bay with TB cleaner trying to find any other possible leaks
• Replaced PCV Vavle
• Replace Rear Valve Cover Gasket (suggested and needed)

I do have an exhaust leak somewhere under the car it sounds like (Y-Pipe flex section perhaps?). Would this cause a lean code CEL? I have the Apexi tuned a little bit....do I need to go get an A/F Dyno and tune it better? The guy who tuned it had the values for a similar setup written down in a notebook.

All of my maintenance is up to par. I'm anal about maintenance.

I NEED HELP. My inspection ends at the end of this month and I've spent about $275 and 3 weeks of time trying to combat this myself. I do not want to spend $300 on a new MAF sensor either. Could it be my O2 sim? I have another new that I never used cause I thought my other one died (light wasn't blinking but it's been fine for like 8 months since)...but if the sensors controlled by it were bad...I'd be getting a P0172 (bank 2 lean). Is it a result of my cheap EBay ram air intake? I'm getting a 5th Gen. complete intake that I'll be installing as soon as I get.

SOMEONE HELP ME. PLEASE!

Here is how the bay looks right now:

when i first got my car i bought a OBD TO CHECK AND SEE IF THERE WERE ANY PROBLEMS WITH MY CAR...TWO CODES CAME UP RUNNING LEAN IF BANK2.. AND KNOW SENSOR...SO I GAVE MY CAR A REGULAR TUNE ...CHANGED THE SPARK PLUGS,FILTER, ETC...STILL FLAGGED THE SAME TWO CODES AFTER I RESET IT... SO THEN I I BOUGHT A NEW KNOCK SENSOR AND INSTALLED IT. RESET THE ECU AT THE SCREW AND WITH OBD AND BOTH CODES HAVE BEEN NON- EXISTED...SO TRY TO CHANGE THE KNOCK SENSOR!!!! IT PROBABLY TIME TO CHANGE IT'S DUE FOR A CHANGE.

[IlyaK]

I did change the knock sensor during the 00VI install.

[Nycist]

could be a dirty injector.....ny gas stations are notorious for watering down their fuel. run some injector cleaner or get your injectors cleaned. try getting gas from another station..

[IlyaK]

Done that.

[altezzablazes]

so if it's not you mass airflow and you already had change your stock usim to 00vi .. with the 5genn injectors do they flow well????check for a crack or vacuum leak in the OOvI they are made of plastic... also check fuel pressure ....Soory for not being much help!!!

[IlyaK]

Wouldn't I have a misfire if that was the case? If a cylinder was starving for fuel, it would sputter and I'd be able to tell. My car drives 100% fine.

How do I check the flow of an injector?

[Feldman]

if i'm not mistaken it is your o2 sensor which tells your ecu what your a/f mixture is like which determines if you are running rich or lean so it can adjust. Since you have an o2 sim i bet your sim is telling your ecu you are lean which means it is probably trying to adjust and you are actually running really rich.

I think you said you had another o2 sim above, i would try and swap that in. you may also need to clean or change your plugs on that bank if you have been running rich for a while they might be fouled.

[99BlackMaxMS]

I had a bad vacuum leak at my EGR which caused me to throw the P0171 along with the occasional 2 rear heated O2 sensor codes. I fixed the vacuum leak and I haven't seen the code since.

[IlyaK]

Originally Posted by Feldman

if i'm not mistaken it is your o2 sensor which tells your ecu what your a/f mixture is like which determines if you are running rich or lean so it can adjust. Since you have an o2 sim i bet your sim is telling your ecu you are lean which means it is probably trying to adjust and you are actually running really rich.

I think you said you had another o2 sim above, i would try and swap that in. you may also need to clean or change your plugs on that bank if you have been running rich for a while they might be fouled.

I guess I could try that....and plugs aren't expensive so I'll have to pick three of those up.

Originally Posted by 99BlackMaxMS

I had a bad vacuum leak at my EGR which caused me to throw the P0171 along with the occasional 2 rear heated O2 sensor codes. I fixed the vacuum leak and I haven't seen the code since.

Did you swap the EGR during your 00VI install? We took it apart...maybe that is it...didn't think of that.

[IlyaK]

Regarding the O2 Simulator from a post above...thinking about it...I don't think replacing it would matter unless my other one isn't blinking away (haven't looked yet, it's raining).

The right bank (PO171 - P0172 is left bank) is the one closest to the firewall. That O2 sensor is the only one back there (the one I just replaced). The simulator doesn't control that one.

[99BlackMaxMS]

Originally Posted by IlyaK

I guess I could try that....and plugs aren't expensive so I'll have to pick three of those up.



Did you swap the EGR during your 00VI install? We took it apart...maybe that is it...didn't think of that.

No we didn't swap the EGR iirc, we just needed to permatex it and make sure that it was sealed...as they don't match up perfectly otherwise. I think the two O2 sensor codes were unrelated as sometimes they would pop up with the P0171 and sometimes they wouldn't.

[IlyaK]

Hmm...okay. Now that I think about it...we loosened the bolts that hold it to get the manifold on...then retightened. The guy who did it swears there is no leak there....and he's done so many VQ related amazing things that I believe him.

If I sprayed TB in there (not just a vac. hose) would that hurt anything?

[Sentientbydesig]

Why not, just plug the O2 directly into the exhaust where it's supposed to be. If the exhaust is actually richer than the O2 sim is reporting, then plugging it in directly should fix the problem OR send it in the opposite direction.

[IlyaK]

Originally Posted by Sentientbydesig

Why not, just plug the O2 directly into the exhaust where it's supposed to be. If the exhaust is actually richer than the O2 sim is reporting, then plugging it in directly should fix the problem OR send it in the opposite direction.

Can't do that...no more cali pipes...

[Sentientbydesig]

Originally Posted by IlyaK

Can't do that...no more cali pipes...

Ah, that would make a difference. I guess that's one of the problems with modding. There's a point at which you go to far and start causing problems.

Reminds me of when I used quick epoxy to hold the vacuum tubes on my intake. 30 mins of summer driving melted them off.

[99BlackMaxMS]

I'd just double check everything for vac leaks, you can have a major one and not even notice a difference, as that is how it was for me.

[IlyaK]

I sprayed TB everywhere. That would have told me if I had a leak. No?

[maxgtr2000]

It is possible that the exhaust leak is causing the code. In an exhaust leak some oxygen actually gets drawn in from where the leak is because of the velocity of the exhaust. This could trigger the o2 code. Not to mention it has been said the rear bank on maximas run lean sometimes because the way the fuel lines are set up to feed the front injectors first and the rear bank second. I was trying to find the thread where someone actually blocked off where the fuel line feed usually goes and made a t in the rubber line that holds the fuel rail together, this gave it a more even feed. I would probably do that if nothing else works.
Not sure of you read this.http://forums.maxima.org/6254179-post7.html

[IlyaK]

Originally Posted by maxgtr2000

Not sure of you read this.http://forums.maxima.org/6254179-post7.html

Hmmm...perhaps I should do this?

But anyway...

Update as of 11/9/08.

On thursday night, I took off the y-pipe to see if I could track down a leak...thinking that's what was causing my lean code. Sure enough, the rear gasket between the header and the y-pipe was completely burnt. Luckily, I had two Nissan gaskets for that part of the exhaust. So, I swapped out both front and rear gaskets. Called it a day and started putting it back together.

Long story short, I stripped one of the studs on the rear header/manifold.

Friday and Saturday (4hrs friday and 7hours saturday) I spent taking the radiator, cross member, manifold, and both rear headers off and swapping in the OEM fed. spec set I had along with new OEM Nissan Gaskets for between the block and headers, and headers and y-pipe.

Everything runs fine, car is much quieter, and I can't really hear any exhaust leaks anymore.

Cleared the code, and after about 25 miles I still have P0171.

My question is...should I get new gaskets for between the headers and y-pipe since the ones I put there (Nissan ring type) were already used once the day before? I'm thinking since they got crushed/smushed during the first install...they aren't holding as well now...even with special exhaust sealant.

Regardless, my issue is NOT gone and I still have a CEL. Of all the guys who have turbo'ed, sc'ed, and otherwise modded their engines...NO ONE has any idea what is causing this for me?

I've replaced:

• O2 Simulator
• Headers (from SS AutoChrome to stock Fed. Spec.)
• Oxygen Sensor located on the left side of the IM near the firewall (rear part of the Y-Pipe)
• Replaced Y-Pipe Gaskets with NEW Nissan OEM
• Replaced Header Gaskets with NEW Nissan OEM
• Replaced rear valve cover gasket with NEW Nissan OEM (had an oil leak there after the 00VI swap)
• Replaced Fuel Filter
• Replaced Knock Sensor
• Checked the injectors for abnormal clicking with this stethoscope device type thing for cars
• Tried three different MAF's
• Tried different boost sensors (located on intake snorkel - had a different code for it but I thought it would be worth mentioning here)

I have 6 brand new spark plugs that I didn't install yet...but otherwise I don't know what else to do or try. I'm at wit's end.

ANYONE? PLEASE!?

[Professor]

Hmm iam having the same exact issues, i posted in 5th gen, the PO171 , nothing helps. If you find the cause, PLEASE pm me, i replaced MAF< O2 sensors, reinstalled OEM airbox , new vac lines,checked injectors with noid lights, no issues, i cant find the source. i can only think of fuel filter or fuel pressure regulator, but the filter on my 5th gen is in the darn tank........ stupid design.

[IlyaK]

Originally Posted by Professor` <