Curious because the link you provided mentioned this

" If the sensors start to fail, or if the cats start to fail, the post cat sensors will tell the ECU to make air/fuel changes in an effort to reduce emissions. In most cases, it will increase your "Long Term Fuel Trim" making the car run richer."

The part about increasing fuel trims to reduce emissions makes no sense at all. Unless combustion temps are way to high and you are adding fuel to reduce NOx, but of course 02 sensors aren't going to give you a 5 gas analysis to confirm or deny the presence of NOx.

Even with all that said, if you are pulling your secondary 02s out of the pipe enough to avoid throwing codes, according to the statement in that post, your ECU would not be looking at secondary 02 readings for anything but catalyst monitoring.

On the other hand if your primary sensors have failed and the ECU is aware of this, I could see the ECU falling back to the post-cat sensors as a failsafe but that's just pure conjecture.

In other words, if you are not throwing any 02 or catalyst efficiency codes, whether that guy's statement was true or not, it should have no basis on your situation.

 

All I know is closed loop A/F was semi-unstable with them, and spot on 100% of the time without them with no changes to the tune whatsoever other than clearing the learned fueling. I had cleared the fueling several times with them and even played with the tune... The ECU kept overcorrecting idle (bouncing between rich and lean), and causing its own rich condition when cruising no matter what I tried...even leaning the fawck out of the entire map wouldn't stop it from dumping fuel at times. The only way I can explain this is if the ECU is in fact using the lower sensors for fueling changes at least some of the time.

If there were a problem that caused my ECU to 'fail over' to the lower sensors, don't you think I would have had a code or two?

Maybe the 2004.5's being the first model with widebands, they put more emphasis than later years on the narrowbands?

 

Good call. We can make educated guesses here all day but need some hard data to come to a real conclusion.

 

^^^ I don't know exactly how the Nissan ECU's use the downstream O2 sensors. But i know for a fact that Chrysler(I was a Chrysler master tech for 6 years) uses the downstream O2 sensors to trim in LTFT over the course of extended drive cycles. Also from the many seminars and tech classes I have been to they state that other manufacturers do it as well, and that many manufacturers use downstream O2 sensors for more then just checking cat efficiency.

Like I said I cant speak directly to the Gen2 Nissan ECU's but I know other companies that do...

Not debating of concluding anything...just adding info to the post...

 

Thanks for the info... hearing stuff like this makes me want to do some driving and logging tests and do a quick write up on the results... I don't think it's worth it to spend another full day logging and wrenching just to prove to others what I already know...my LTFT's are happy now, so I'm happy. That's all that matters.

 

It almost sounds like you believe that:

Evidence > Faith

/sarcasm/ How dare you! Don't let the fanatics find out.

 

I removed my 02 Extenders this weekend, and after putting some miles on it my cruising and idle AFRs are now much more stable. (i didnt clear my learned curves) but my AFRs used to fluctuate from ~12.9-14.9 on the left bank crusing and idling, but not anymore.

 

good to finally hear it's not just me! I put over 500 miles on it since removing the antifoulers and the A/F is still perfect and not even a CEL...go figure.

 

anyone with "CEL fix" style high flow cats or test pipes seeing this same issue?

 

I had the kinetix test pipes with the built on foulers and my idle was really rough. Kept fluctuating. so I just got the Berks test pipes and used the non fouler bunk and my idea returned to normal. Felt more responsive also. I don't have a wideband on my 03z but that's what I've noticed.

 

I don't think all non/anti foulers are alike. I would assume the farther it extends the more it affects the ECU trims -- on mine the length was about 2" but enough to mess up the trims.

 

My wideband would jump like crazy at idle as well.. Once my new sensor gets here I may have to check it out and run some logs..

 

I can't imagine that the O2 sensors wouldn't be staying warm enough to read the AFR reliably at idle, but I read today that O2 sensors have to be pretty warm to read accurately. It seems that some O2 sensors have built in heating elements to help them maintain the necessary temperature, but others do not.

Also I read that with boosted engines, and with test pipes and free breathing systems, less heat is retained in the exhaust system to keep the O2 sensors warm enough. I think that they are supposed to be up around 600 degrees for proper operation.

I may be WAY off on even mentioning it, but could that have anything to do with what you're seeing when using the non-foulers?

 

I can log the heater status on the downstream sensors so I would assume they have built in heaters. They do work at idle, even before the upstream sensors at first startup. Also I have heard that at first startup a hot wideband could be damaged by sudden moisture (cold startup)... the ECU appears to delay the warmup / use of the upper sensors -- I don't get a good reading off them for at least 30 seconds after first start. The downstream sensors start sending signals almost immediately.

With the nonfoulers the AF would start up rich (normal), then it would abruptly go closed loop and bounce around until it gave up and went open loop / rich again... this cycle would repeat for a minute or two until it finally 'got it'.

Without the nonfoulers the AF would slowly creep from rich to 14.7 then stay there... no abrupt bouncing and the ECU would stay in closed loop. It's like this while driving too... the downstream sensors are like 'dampers' for A/F corrections.

 

Good work! I have kinetix HFC and i am getting the catylist efficiency CEL. I was thinking about non foulers, but now I will keep my current setup and just get a tune to get rid of the CEL

 

So should we keep our non foulers or take them off before tuning?

 

You should take them off in general, especially before getting tuned -- since you're getting tuned you can just delete the codes if you have them.

 

I'll take mine off tmoorrow and see what it does for my SES light. I don't have any way to check a/f though so sorry guys

 

You should be able to feel or hear a difference in idle and in cruising around... reset your ECU while you're at it so it can re-learn your trims with the proper signals.

 

Could these observations be caused by an air leak around the antifouler?