If you've got antifoulers on your lower sensors, take them off... see my other thread. If you've got a true dual, make sure you've got a crossover or H pipe on it.

what thread?

I dont have antifowlers and it all goes into a single pipe to the turbo so no duals here...

https://my350z.com/forum/tuning/5182...vs-tuning.html

I know it might not pertain exactly to you but it's more of a general statement for others in the same boat. Basically pointing out that the lower o2 sensors _are_ used for corrections.... When I had non foulers installed my ECU was adding fuel even though the upper widebands were showing rich. I would imagine a clogged cat or any kind of leak after the upper widebands would cause the same problem. Pulled the nonfoulers off and the A/F is now dead on 14.7 and no more overcorrection.

A Thought
 

From someone who has absolutely nothing to do with this issue since I have no mods at all. Just wasting time today reading and thinking about this problem.

At work we just built/shipped a fairly advanced machine that tests these A/F sensors performance to Bosch in SC. Neat stuff. It had a robot that loaded/unloaded the sensors 10 or 12 at a time, LabView running the tests.

Anyway, the thought occurred to me that maybe the ECU is screwing with the A/F correction intentionally as a test. Ramping the A/F up and down and charting the result. Is this plausible? :dunno:

I will match that.

So has anyone logged the downstream sensor voltages while this is happening?

what is the channel name for those? I logged every CAN channel that haltech would allow me to log so i'm sure i have it somewhere.


also, mine would be difference since my haltech widebands are running the corrections and not the oem ecu like in your case so it probably doesn't apply to my situation. :(

Sensor 2 for both banks. The OP was dealing with stock ECU... haltech is a completely different animal, agreed... but one would think it wouldn't completely ignore the downstream o2 sensors. At least in the case of the stock ECU (or osiris flashed) the downstream sensors sometimes take priority for corrections.

ya, on the haltech the rear o2 sensors do nothing (as well as the fronts do nothing) except for keep the ecu happy. Ive had them out of the car with no issues except a CEL code.

have you swapped cats of the bad side?

My money is on a glitch in the ECU, like I told ya a year ago! :p

Can a bad wiring harness ground cause this problem?

( I have it also)

It is not causing THIS problem, but I suppose a bad or flaky ground could cause weird voltage reading.

That's an ambiguous statement. People have replaced the ECU to no avail. Something with the exhaust cam timing? Something with the UpRev programming codes not complete with the ECT?

We logged cam phasing- not the issue.

^ This seems to be a likely culprit if the latter statement is true. If there is a leak between the upstream and downstream O2 sensor and the stock ECU is correcting for it, then a rich O2 value may still result in overfueling.

How do that bank's plugs look? I've got a similar issue and noticed my plugs say the opposite to what code is being thrown (p1283 for 3 ultra rich plugs). I'm guessing there is something tricking the ECU to feel it can't dump enough fuel in to correct. I too have changed both O2's so I'm searching for a place that does leak testing (smoke machine).

I actually just got my car back after a retune and the code is now gone, passed emissions without a problem.

I was going to guess it was tune related before I even looked at this post.

After driving my car for a while, I think the car needs to be driven on the road or something. A steady driver on the dyno and the codes may not come up.

Loads vary, I don't think a dyno can replicate those situations.

i had the car tuned and then driven by the tuner for a few miles, then he decided to tune some more. After a few weeks he got the tune to the way he thought was good and after 60 or so miles of spirited driving i managed to pass emissions and now about 200 into it without any check engine lights. I would def say this is tune related.