onagao

Yeah. Well, my code hasn't come back, but the imbalance has returned just as before - despite swapping both sets of sensors now. So it's not the O2 sensors, for sure. I hope Mother Nissan can help

mzdfc3s

iTrader: (2)

i would still be interested in seeing your o2 voltage data vs rpm if you get a chance. looks like ill have the sled till at least monday now...

SRT BRAD

I have a suspicion that something might be wrong in the valve train on the bank that is giving you the code.

You say that you hear a "burping" noise from the engine, along with a "flat spot" in your RPM range. I can't personally hear the noise myself, nor have I driven the car so I can't say 100%. But I have seen 3 separate times where for whatever reason an exhaust valve won't open, or only partially open (bent pushrod or broken rocker, etc) and it will cause a popping sound.

Remember your basic engine operation? Intake stroke: Piston it at TDC and the intake valve opens as the piston comes down. Compression stroke: Both valves are closed and the piston moves up, compressing the fuel/air mixture. Power stroke: Both valves still closed, spark plug fires forcing piston down. Now here's where the problem is. Exhaust stroke: piston moves up to push the exhaust out of the combustion chamber, but if the exhaust valve won't open for whatever reason, what happens?? The exhaust is compressed again. (The exhaust does not leave the combustion chamber via exhaust valve)

So what's next to happen in the engine cycle? Intake stroke. Right now there is compressed exhaust in the cylinder. Now the intake valve opens as the piston comes down and lets compressed exhaust out the intake giving you that "burp" sound. Similar to a backfire.

The rich code is being set because the O2 sensor isn't reading the oxygen it should be seeing from that cylinder, because there is no/little exhaust exiting that cylinder. In all of the cases I've seen, the rich code was accompanied by a misfire code leading me to that specific cylinder, but for whatever reason you're not getting a misfire code.

I hope this helps. I may or may not be right (tough to give proper diagnosis when I haven't checked the car out myself) but hopefully it will lead you to the problem. Hope to hear what the outcome is.

mzdfc3s

iTrader: (2)

well this is truly another thought. that does make complete sense, i follow what your saying. now i could suggest this to nissan, like i have made before, and they usually only listen to half of what i say. they're going to do whatever they want anyhow. worth a try i guess.

wonder what would cause that condition?

SRT BRAD

I have personally seen rockers literally fall out of place on the 3.7L and 4.7L Chrysler V6's and V8's. It's not a common enough of a problem for there to even be a tech tip or service bulletin, but it's still a known problem. Chrysler tech support doesn't even know why/how the rocker falls out. There has never been damage to any of the ones I've seen. I've just put them back in and none of them have ever came back. I have never had a VQ valve cover off, so I can't say for sure if it's got the same setup as a Chrysler, or if it's even the same problem.

After thinking about this more, it would be really nice to know if Nissan's scan tool is capable of doing a power balance test. I've never used a Nissan scanner, but I know Ford/Mazda's tool does. If they can, they can run the RPM up and see which cylinder is putting out less power than the rest. This could lead them to the cylinder that is causing the problem. Even if they can't do a PBT, they already know what bank the problem lies in, so a valve cover removal and inspection of the valve train might be enough to find it.

onagao

Well, would a physical problem like that still cause the datalog to show an overcorrection for the bank of 10-15% more than the other? I would think it would correct the other way (i.e. pull fuel when reading rich) as opposed to adding despite the rich reading.

mzdfc3s

iTrader: (2)

no i think the ecu is correcting accordingly but just isnt smart enough to know its correcting for the wrong reason

SRT BRAD

Yes mechanical problems/wear can result in PCM driving up/down fuel adaptives. It has been proven time and time again.

You're correct, it would make sense that it should be pulling fuel rather than dumping more in. I only suggested the possibility of a valve train issue due to the noise that's coming from the engine. Popping sound coming from the intake similar to a small backfire is a classic symptom of an exhaust valve/circuit problem.

Auto-Tech instructors can preach the theory aspect of it all they want. But once you get out in the field and experience all the crazy **** that doesn't make any sense, you start to learn to go after what makes most sense, rather than focusing on what doesn't. Hell, sometimes engineers don't even have all the answers.

mzdfc3s

iTrader: (2)

So this is the latest horse **** from the dealership....called this morning to see if he heard from Nissan and he didn't so I pitched him the exhaust valve theory. Of no surprise he really didn't give a **** about my thoughts. Later he called back and said that mother Nissan told him to check the clamp between the header and cat for a leak but only when the car is cold started? Ive really been patient with these guys the last couple months but this is nonsense now. There's no leak, if there were a leak only when cold started then my o2 readings would normalize after the car got warm assuming the "leak" closes shut after all the heat expansion.............errrrrrrrrr

D_K

I had this code for two months after I replaced my stock ypipe with an aftermarket one. Car ran fine and then one night I was driving hard and then got that code. I took it to the dealer and as it turned out the cause was that one of the gaskets (aftermarket ones) that were used to replace the factory ones when the install on the ypipe was made blew out and there was an exhaust leak on the driver side of the fork in the ypipe where it joined with the driverside testpipe. Got the gaskets replaced with factory ones at the dealer, reflashed my ecu with my accessport and its been two weeks now of daily driving to work (over 400 miles) and no CEL.

So I would seriously have the dealership replace all of your exhaust gaskets.

mzdfc3s

iTrader: (2)

could be.....they've already looked at the exhaust ad nauseum. that code has taken me up to 850 miles to reproduce and that was when the ecu was reflashed and all learning parameters reset. you may have indeed had an good exhaust leak but i wouldnt be surprised if it did come back. let us know

D_K

Yes , I have gotten the code back within a week before I had it looked at. Another thing to look for is for cracks on your headers if they haven't checked that or intake leaks.

onagao

Well, I've replaced my headers as well as the gaskets. Still have the problem, and after a long trip to Oklahoma City, the P2A00 code has come back.

I'm not sure if I understood correctly, did the injector replacement actually fix the problem, or has it come back and thrown the code since then? The reason I ask is that I'm contemplating checking out mine, but I don't want to spend any more time/money on something that isn't going to actually work toward fixing this damned problem.

mzdfc3s

iTrader: (2)

by the looks of it the injectors were only part of the problem. they actually problem went bad from being over-worked for so long only worsening the rich condition. code came back within a week. i am really favoring the valvetrain idea at this point but im having a hard time convincing the dealership to look at it. i just dropped it off again last night. they say there could be a leak in the exhaust only when cold starting according to mother nissan. i know this isnt the issue but at least its there again.

injectors are really easy to check, just grab an ohm meter and test resistance.

onagao

Okay. I'm having my injectors checked today, so we'll see what that holds for my situation. As far as them being easy... sort of. You still have to remove the intake plenum to get to them.

redline06

Lemon law!

onagao

All of my injectors turned out fine. The resistance read-outs were all consistent and within the appropriate range per the FSM. It has me thinking that maybe it's a fault in the ECU? I did some more searching and asking around, though, and I have found a few weak leads in terms of information:

I found this link @ the 370Z dot com /intake-exhaust/12752-cel-code-p2a00-2.html

(it won't let me include the full link... wtf)

Guy with a 370Z had the same issue, but fixed it by replacing the gaskets between the manifold/headers and cat section. I have a hard time believing it's that simple.

My brother is also suggesting that it's related to the MAF. However, I have a hard time understanding how that would affect one bank and not the other in the correction and adjustment taking place.

mzdfc3s

iTrader: (2)

well i bought the faulty ecu idea until they replaced it and the code was back. remember the maf's and O2's were all replaced too.....i really like the valvetrain thoughts but the only thing out of the equation is a misfire code. back to the guy's leaky gaskets in the 370 and a few others maybe this is it. until now i really thought when the dealership told me there was no exhuast leak i believed them.

UPDATE:

they called today and said there was a crack at the weld on the bank 2 cat, same as code. they must have taken it off to have to find it, i dont know. i asked to see it when i go and they obliged. so i will take pictures to verify. maybe this is it. and the reason i think my injectors went bad is because i literally drove this car for 20K miles in this condition without investigating the CEL. driving it that long with the ecu overcorrection rich probably would drive the injectors to fault too.....well see. i will be able to tell as soon as i get the car because im bringing the laptop to plug in and monitor. if the O2 readings are nearly the same on each side then problem fixed. right now they read ~ .875v bank 2 and .450v bank 1 at idle. clearly different. keep ya posted. supposed to pick up tomorrow. cheers

onagao

I guess I had missed some of the details in your previous posts. I usually don't do that, but this should certainly be interesting. It makes me want to get back under my car and look at those pipes and gaskets. Btw, I think the reason my voltage looked weird to you is because the voltage readouts for the HRs are different than they are for DEs. They changed the type of sensors they use, I believe (one of the reason there are some difficulties with Uprev support for the HRs).

mzdfc3s

iTrader: (2)

well car is back again, i have honestly lost count how many times we have gone through this in the last 2 months. i really didnt get a chance to drive the car yet just home. i did have time to hook up the data logger and check things out. so nissan said they found a cracked weld on the bank 2 cat. i unfortunately did not get there in time to see it for myself.

so the data logger on just sitting in my driveway at idle i still see the same condition present same if i hold rpms at 4500 for a few seconds and the fuel trims are off the reservation now. i think the fuel trim whacko **** is probably because the ecu is "raw" since the reset the learning parameters...just a theory.

i dont know folks, well see in a few days but i would still be willing to bet a few beers that effin code comes back.......