O2 Feedback

[89CAL]

Hi

Noticed my car was leaning out on lean cruise today, had previously been fine.

Went to play with the tune and my O2 feedback was off, so turned it on and the AFR hunts quite bad. It cycles between 14.6:1 and 15.6:1 at 60km/h (only had time to look at the 60km/h lean cruise AFR's)

Was just wondering if the AFR's are supposed to hunt like this with O2 feedback on, and is it worth having O2 feedback on at all or just tuning the INJ map at the cruise points to achieve constant desired AFR

Played with the INJ correction for O2 feedback, but didnt seem to make a difference. Came home for a look and in the Celica Forums and it says that the INJ correction value is the maximum value in the INJ Map that it will apply O2 feedback to

If i understood it right

Is an APEX'i Power FC in an R33 GTS't. Tuning with FC-Edit and FC-Hako interface

Thanks

[blind_elk]

On cruise, the O2 is supposed to cycle rich - lean - rich - lean , it's called "closed loop". It's near impossible to exactly tune the system so that you get stoichiometric mixtures, so the ECU uses closed loop to continually make adjustments to the mixtures around the stoichiometric point.

[89CAL]

Oh I didn't think it was supposed to do this on closed loop (or at least not as much)

Seems less economical then setting the map to run at a set AFR which it had been doing. Except then it seems to vary slightly depending on coditions I guess?

[JonnoHR31]

it sounds like your maps tuned leaner than 15:1 which will cause cycling problems with a power fc and o2 feedback. basically with o2 feedback turned on and a lean map it'll inject off your base map, read lean from the o2, drop fuel in until it reaches stoich then lean back out to the map again. if its tuned properly just turn o2 feedback off, you can get better economy without it. or the other option is to use your wideband to simulate a narrowband but change the values so the ecu sees stoich around the same AFR's you've tuned for (eg 15.5:1).

as for the o2 feedback setting your correct, it simply sets the correction figure limit for using o2 feedback, meaning any cells lower than this number will use o2 feedback (under the right cruise conditions) and any cells higher will ignore it completely. I usually just set it to around whatever figures are on the map in the area where you start going from cruise to light boost, usually around 14:1

[89CAL]

Ah sweet as, that's what it will be doing then. Lean cruise was set around 15.5:1 but all of a sudden yesterday it was leaning out to close to 17:1. On boost the AFR's were still the same so I saw O2 feedback was off and thought it must have turned itself off

So not sure what's happened to make it lean out like that but I'll tune it back to 15:5 and just leave O2 feedback off I think, seems like the easiest option.

Thanks heaps for that, explains exactly what was going on and now I know how the O2 feedback works

[Hanaldo]

Ok so quick question about the o2 sensor,

Would having it disconnected cause any sort of issues while the car is cold? I have noticed that while my car is cold and I am cruising on decel (using the gears to maintain speed, ie. going down a hill in 5th my car will just sit at 80km/h without needing to apply the brake or accelerator), or while cruising with only very slight throttle, my car - for lack of a better word - 'surges'. What I mean is that it feels like the engine is slowing down a little bit and then it speeds back up again. It's not really enough to affect my speed as the speedo hardly registers it. But it's enough that I can feel it happening.

As far as I can recall, it has only started happening since my tuner disconnected my o2 sensor and tuned around it. And it only happens while the car is cold and as I understand it, only while it would be in closed loop. Is this likely to be the o2 sensor or something else, TP sensor maybe?

Sorry if I'm hijacking, it seemed remotely on topic

[89CAL]

Do you have a power fc? If so check your hand controller to see if O2 feedback is on. If it's on and your O2 sensor is disconnected it may cause a problem - see your tuner to check if he has tuned it for lean cruise then you should just be able to turn this feature off

If it's off already then I'd say go see your tuner as well and ask him about it. It could be the TPS I guess as it helps determine the load point on the map. Not to sure if it would cause the problems your having but

[Hanaldo]

Do you have a power fc? If so check your hand controller to see if O2 feedback is on. If it's on and your O2 sensor is disconnected it may cause a problem - see your tuner to check if he has tuned it for lean cruise then you should just be able to turn this feature off

If it's off already then I'd say go see your tuner as well and ask him about it. It could be the TPS I guess as it helps determine the load point on the map. Not to sure if it would cause the problems your having but

Nah, NIStune. My tuner did say at the time that my o2 sensor was causing problems so he had to disconnect it, but it didn't matter because he just tunes around it anyway.

My car is booked in for a retune next week, but at a different tuner. So I wanted to see if I was correct about it being the o2 sensor or if I should ask my new tuner to investigate.

[89CAL]

Don't know enough about the nistunes but I thought seen as they run similar to the stock ECU that it might be expecting an O2 signal.

As I said though, I don't know enough about the nistunes to confirm this is what happens

[GTSBoy]

Nistune IS the stock ECU, so it CAN run exactly as the factory closed loop. But you can also turn off O2 feedback on it (by various means) exactly per the PFC example.

Hanaldo has a Neo engine yes? In which case, you can't turn off the O2 feedback in the conventional sense. You have to do it by bumping the feedback temperature limit up real high. There is no "closed loop" section of the fuel map like there is on most other Nissan ECUs (or rather, the O2 feedback flag is enabled across the whole fuel map and you can't turn it off). The selection of when to run closed loop is done by arcane means in the bowels of the ECU code and there is another map, the VE map, which covers a smaller load range than the fuel map that plays a part in that decision, and the resulting injection pulsewidth. It's all rather annoyingly complicated. Which means that there might be unexpected consequences of disabling/disconnecting the O2 sensor and not having the VE map adjusted to suit (however the hell that would be is not known to me).

cheers

[blind_elk]

The ECU won't be in closed loop when the engine is cold, because the ECU is running the engine quite rich while the engine warms up.

[Hanaldo]

So more likely to be TP sensor??

[JonnoHR31]

yer if it only happens cold you can rule out o2. is it cycling in and out of fuel cut? or is it a different kind of surging?

[rob82]

yer if it only happens cold you can rule out o2. is it cycling in and out of fuel cut? or is it a different kind of surging?

Sounds like on/off decel fuel cut.

And to the original poster it sounds like you have a dud o2 sensor - best way to test them is force the engine to run rich and then lean and make sure it goes above 900mV and below 100mV. The switch to high and low should be within a second.

[Hanaldo]

yer if it only happens cold you can rule out o2. is it cycling in and out of fuel cut? or is it a different kind of surging?

Surging is a bit of a misleading term I think, I don't think it is really surging. I don't know how else to describe it though.

It's not like a TP cut or anything like that where it feels like you have hit a wall. It's much more subtle. It's like if you were driving along, and you just tapped the accelerator quickly. It speeds up a little bit, slows down a little bit, speeds up a little bit, slows down a little bit, etc. Very minute, so hardly registers on the speedo at all, but you can hear it and you can feel it. Only ever while cruising, and only when it's cold. As soon as you put your foot down or decel quicker or the engine is warm, it doesn't do it.

[rob82]

Nistune IS the stock ECU, so it CAN run exactly as the factory closed loop. But you can also turn off O2 feedback on it (by various means) exactly per the PFC example.

Hanaldo has a Neo engine yes? In which case, you can't turn off the O2 feedback in the conventional sense. You have to do it by bumping the feedback temperature limit up real high. There is no "closed loop" section of the fuel map like there is on most other Nissan ECUs (or rather, the O2 feedback flag is enabled across the whole fuel map and you can't turn it off). The selection of when to run closed loop is done by arcane means in the bowels of the ECU code and there is another map, the VE map, which covers a smaller load range than the fuel map that plays a part in that decision, and the resulting injection pulsewidth. It's all rather annoyingly complicated. Which means that there might be unexpected consequences of disabling/disconnecting the O2 sensor and not having the VE map adjusted to suit (however the hell that would be is not known to me).

cheers

It's unlikely to be too complicated - more than likely just a 2d scaler with tsp enable vs rpm.

But yes if you remove the o2 sensor it will trim an extra 20% of fuel in while in the closed loop section of the map. Hope your tuner took that I to account.

[GTSBoy]

The ECU won't be in closed loop when the engine is cold, because the ECU is running the engine quite rich while the engine warms up.

O2 feedback temperature is 30°C standard on Neo. That's not long after start up. Granted, warm up enrichments will still be around for a while, but it could go into closed loop earlier than you think.

Edited August 9, 2011 by GTSBoy

[Hanaldo]

O2 feedback temperature is 30°C standard on Neo. That's not long after start up. Granted, warm up enrichments will still be around for a while, but it could go into closed loop earlier than you think.

Yeh my issue occurs from when I turn the key to just before operating temperature. Not sure exactly what temp it is when it stops, probably around 60-65ish degrees (water).

[89CAL]

Guarantee its not my O2 sensor. It's not even 5000km old

[rob82]

Guarantee its not my O2 sensor. It's not even 5000km old

Is it genuine? Is the sensor gnd in tact and not chassis earthed? Log the o2 sensor and check peak to peak voltages and the average voltage.