AFR difference between the banks

Jordo!

I don't think it's ever in open loop. The target maps cover all load ranges, and that means there is always a STFT and LTFT. It's just that beyond a certain load range, you can set the targets to whatever you want without the ECU trying to wrestle the engine to run close to stoich (assuming it does that -- I seem to recall uprev commenting on this, but no idea if its accurate).

The cylinder trims vary most likely due to flow variation -- massive correction implies either the sensors are off more than one would like or your set-up is just flowing unevenly, which to some extent is unavoidable.

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Mitco39

The car is in open loop under load. You can watch the trims sit at 100% while the car does its thing (which for people trying to follow a 100% means the ECU is not making any adjustments to the correction tables). Then once the load drops down the trim starts again. Uprev however doesn't have the tables mapped for when the ECM switches from open to closed.

It does make sense that there will be a hint of variation per bank. However these trim values everyone are talking about are only active during open loop power enrichment mode. When you are in closed loop the ECU will over ride whatever "trims" you set in when it starts listening to the 02.

For example, lets say you take bank 1 and cut the fuel down by 25%. So on 1,3, and 5 you set the trim to 75%. The fuel relearns are then cleared and the car is set to sit at a constant load under closed loop. At first you will see the trims on bank one sit at 25% as it tries to take your changes into account and yet keep the 02 on that bank happy. Now as you drive you will see the LTFT (long term fuel trim) start to react to the constant high STFT and it will increase to help bring the STFTs back into a better range.

Once the LTFT stabilize you will then see car will run at or around whatever the AFR is set at now completely disregarding your bank trims. Now under WOT this is not the case at all.

I agree that these trims are great under WOT runs, you can clearly see that if one trim bank is constantly higher than the other bank you can then see and adjust these bank trims to compensate for that and ensure that when you do go WOT both banks are running very close to each other in terms of AFR.


If I am wrong I would like to know it. I have been tuning vehicles for 4 to 5 years now and this is the same logic used on the cars I tune. This UPrev setup might be different, but in my 6 or so hours of log time on the weekend this seems to be exactly what is happening in this case as well.

Mitch

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Jordo!

That all sound spot on -- I wasn't entirely clear on whether there was a real open or closed loop like there was on narrow band O2 controlled AFR's, because, yeah, as you noted, uprev doesn't clearly indicate it. I thought since it had wide band (5 volt?) sensors it just maintained a close loop throughout, maybe forcing the ECU to trim to stoich under low load.

So is there an aggregated LTFT from the closed loop sections of the map that carries into open loop?

Also, what approximate TPS or MAF voltage switches it over? I'm guessing it corresponds to whatever point in the main AFR target map it goes richer than 14.7?

Is that much variance common on an OEM set up or is this strictly due to the plumbing differences for your set-up?

The only other thing I can think of is that one of sensors may just be reading very differently. Have you swapped the sensors to see if the bank difference moves with it?

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Mitco39

Yes I have found that manually setting the correction tables to some very wrong values (lets say removing 30 percent to the constant throttle section) caused the STFTs to constantly sit high until the LTFTs started to take that into account and change to meet the needs of the STFTs. Needless to say you can be way way out to lunch on your correction tables and the ECU will bring it back into check, it will just take longer to do so. And I guess if you bottom out your LFTs then you will get the rich or lean bank codes from there.

It seems like anything under 14afr commanded will put the car into a closed loop situation although its really hard to pinpoint weather its load based or just afr based. With the BP kit as soon as the boost starts to come on its already in open loop and then that is where you can see how your correction tables really come into play because now the ECU is not looking to adjust these values and it just takes it as "correct".

I have looked on many other forums (including 350z and titan forums) and it seems like its a fairly common issue. I am surprised infact that more people have not noticed it. On the forums I did find people were describing the exact same situation however most of the replies were uneducated and telling the OP to check for boost leaks ect. No boost leak or exhaust leak is going to tell the ECU to inject more fuel if it is already running rich.

As far as switching the sensors on the bank, that wont fix anything because the ECU clearly sees bank 1 is running rich. I can see it through uprev. Its sitting at around 13.8-14.2, yet the ECU is trimming like it is running lean.

I have come across a post where some guys have said disconnecting their downstream 02s have helped to fix the problem. The thought is that the ECU is looking to see a certain AFR post cat, since the cats are gone its getting fooled and I would suspect that the ECU may be injecting more fuel to try and light off the cat or heat it up to bring #2 O2 into whatever reading the ECU would expect to see on it. Unfortunately we cannot see exactly what these 02s are doing. I am going to try unplugging both O2s next time I am under the car and remove the associated codes and see what that does to the tune. Some have said it will force the ECU into a open loop situation under all conditions. One way to find out.

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2007 Chevy Duramax - EFILive Tuned By Me
2010 40th W/ Nav - Boosted Performance - UpRev Tuned By Me
The Mrs. Ride -2012 335XI N55 BMW - Cobb Tuned By Me, Built by her
My Build --> http://www.the370z.com/members-370z-...39s-build.html

Jordo!

Switching to open loop is probably both TPS and load based -- the boost just reads as high load (i.e., higher voltage on the MAFs), so the only concern would be if you skew lean under part load with moderate boost. If it's not happening, then I guess its either just load based or weights load as more important than TPS?

As to the 2ndary O2's, I thought if you turned off the DTC for it that effectively got around the ECU taking notice of their presence and attempting to correct -- meaning, you first have to work your way through the the trip detection logic algorithm and then the ECU starts correcting, so if the detection logic is never invoked, the problem is circumnavigated.

If not, and if there's no way to just shut them off or change their threshold, then I bet a lot of us are driving around with weird random fuel trims...

As to switching the MAF sensors -- are you saying voltage readings are the same? If not, it could still be referencing different cells in the fueling map, or if it just aggregates them when accessing the tables, one might be skewing things off more than it should.

On that note, if the MAFs are fine, what about the primary O2's?

Good luck with the 2ndary O2 fix!

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