TheDrain

To preface - I have a 2005 Greddy twin turbo Z with 35k miles in great condition. I recently had it dyno tuned and had boost raised from 5psi to 8psi and was very pleased with the power increase, responsiveness and even increase in gas mileage. The car had been running pretty rich before the tune, to the point where it was wasting a decent amount of fuel and stunk like gas all the time, so this was definitely the right move.

As luck would have it, the next day after having the tune done the car went into "limp mode" (during a moderately hard pull @ around 4500 rpm) for the first time ever and I of course crapped myself since I didnt know what was going on. After sitting all night, the car started up normally, idled fine, drove normal, went into boost normal, etc. The garage ran the codes and determined that both my front O2 sensors went, and that is why the car went into limp mode. P0420 and P0430 were set off, as well as P1271 and P1281.

I dont see how the O2 sensors can "come back to life" and work after letting the car sit for several hours... I was under the impression that if the sensors were fried, they are done for good. I have noticed that if I drive for a long time or run the engine hard for a whole day, I will go into limp mode eventually in the middle of a decently hard boost pull, at which point it doesnt come out of limp mode until i let it rest for a few hours. Is there really any way that O2 sensors can come back to life? Does anyone think that O2 sensors are really the issue? One pair of those codes says "catalyst efficiency below normal threshold" which begs the same question. The fact that extended periods of hard driving increase the incidence would lead me to believe that SOMETHING being affected by fuel output is in need of attention, but what that is, I am not sure. Any input is appreciated, thanks!

SparkleCityHop

iTrader: (30)

What do your AFR's look like during those hard pulls? Do you have a way to log while you're trying to reproduce the event?

RMichael

here is some reading.
http://www.autotap.com/techlibrary/u...en_sensors.asp

davidv

iTrader: (2)

Good article. Very informative.

TheDrain

My AFR's actually look pretty normal until the car goes into limp mode - at WOT it is btw 11.7-12.5 I would avg... once in limp mode the AFR sits at 10, even at idle, and wont change until I turn the engine off for several hours. I only reproduced the event one time after the initial incident - it was during a mild 3rd gear pull in my neighborhood JUST to see if it was still occuring. I was @4,000 rpm and about 6.5psi when it happened, and it was after a day of repetetive driving, about 50 miles on multiple small trips around town. Sadly I dont have any way to log, but I can definitely say that even when the engine is rested and fresh and NOT in limp mode, the AFR's will be totally normal and gas mileage is still decent but if I am in 5th or 6th gear and floor it I can feel a slight "sputter" when approaching WOT once I reach 80-90mph or so, and I can feel a slight loss of power of course

TheDrain

Excellent information, thank you. Judging from the symptoms my car experiences and the funtion of the upstream O2 sensors it does seem like that is the problem... I guess my only question now is

"can these O2 sensors really funtion this irregularly, where they will work well enough to put up with normal driving in limited circumstances and then TOTALLY FAIL (as I have seen twice) - only to come back to life and function properly after ample down time?"

My mileage is much lower than the "recommended" timeframe for replacing these sensors (50-60k) but I am assuming the 600cc injectors feeding extra fuel for the turbos is PROBABLY the culprit for their premature degradation? Any thoughts?

davidv

iTrader: (2)

The O2 sensors seem to be working properly. In the closed control loop the fuel system is attempting to maintain a stoic air:fuel ratio of 14.7:1. When the system cannot maintain this ratio, the ECM shuts down the motor as a precaution. This is the limp mode. Recommendation:

Remove and inspect O2 sensors
Add an extension to the O2 sensor. This fix is similar to members swapping catalytic converters for test pipes.

TheDrain

** as a correction, I am actually running low 10 AFR when at WOT, I just took the car out during lunch and tested it since I have not driven much today, didnt go into limp mode thank god lol

TheDrain

Thanks Davidv, but how do I add an extension to an O2 sensor? Sorry I just havent heard of this before

davidv

iTrader: (2)

http://www.z1motorsports.com/350_g35...oducts_id=3736

djamps

iTrader: (1)

Are you sure you're not maxing out your MAF? Our cars will go into limp mode at peak tq when the MAF maxes out, and there's no code thrown. This can happen anywhere from 350-400whp depending on your setup and tune. If you're on your stock MAF, an upgraded one like the GT or PMAS along with a retune will resolve this.

ALso if you're on a 5AT you might be overheating the fluid.

PS I don't think failing o2 sensors alone can cause complete limp mode. With the lack of other 'obvious' codes I'm really thinking your MAF is maxed out.

TheDrain

I never thought of that either, thats a good point. the performance garage i use has not mentioned anything about the MAF being a possibility but my numbers are such that an upgraded MAF wouldnt hurt anyways. any recommendation on which one you prefer/where to buy?

also, i am 6MT just for the record

lanceccs

TheDrain>>> I am experiencing similiar problem. Have you found the root cause?

Here is my post.
https://my350z.com/forum/forced-indu...ml#post9540516

http://www.youtube.com/watch?v=SbY3zbtg2jo

http://www.youtube.com/watch?v=G3qzUv1EAqc