[Jeff@TopGearSolutions]

Originally Posted by Tiago@VRSF

I doubt it's anything due to lag. It's more to do with how the system measures trims. Ever installed the o2 sensors backwards when doing downpipes? I can imagine the result is similar to that. A car that barely drives lol.

While the temp difference is greater, the heat shouldn't pose too large of a threat in terms of longevity if it's set as close to the collector as possible. I'm just hoping the heat doesn't affect the actual reading.

I'm surprised nobody's gone into the ECU and figured out a way to manipulate the way the system so it reads both sensors in the same way or even eliminates a set.

Originally Posted by M3_WC

This is why HPF should give Cobb a call.

This was already explained and why its better to do it the right way.

Originally Posted by shiv@vishnu

The issue has nothing to do with post cat lambda monitoring. But rather front lambda (pre cat) fuel control. The DME employs two closed loop fuel control routines. One for cyl 1-3 and another, running in parallel, for cyl 4-6. So merging all 6 cylinders and feeding the DME the signal from the front lambda sensors (now reading all 6 cylinders) allows for the two closed loop systems to "fight" each other. And opens up the possibility for one bank to run lean while the other to run rich. The average of all 6 cylinders, in such a case, would still read "normal" and the DME wouldn't know anything is wrong.

Some "tooners" haves suggested modifying the DME code to employ only 1 closed loop fuel control routine for all 6 cylinders. Now THAT would be a step in the wrong direction as you are giving up 1/2 of the stock DME's fuel control precision. Something much welcome when making big power. Heck, if I had a genie, I'd wish for a DME that employs 6 closed loop systems running in parallel, each being fed a lambda signals from 6 individual o2 sensors mounted in each exhaust runner (pre turbo). But you'd only see such excess in extreme cases. But for real world street use, dual bank fuel control is great and just adds to the beauty of the n54 control control system.

Shiv

[dlbrooks18]

Originally Posted by Fundahl

Shiv doesn't have the same issue because his two O2 sensor banks are separated. They are pre-turbo.

Originally Posted by shiv@vishnu

I'm not concerned with heat since the widebands are temp regulated and also for fact that we are running thermal isolators between the manifold and the lambda sensor. For the first week of operation, we purposely ran without the isolators to see of the factory lambda sensors would show any sign of signal coloring. And none were found. But we have reinstalled them just as a precaution. I have no long term concerns at this point. During the design stage of the turbo system, we did some research on lambda sensor operating temp and found the information comforting.

Good info, thanks!

[EastBayE90]

Originally Posted by Jeff@topgearsolutions

This was already explained and why its better to do it the right way.

I was just about to quote that. You beat me to it. Thanks for the new dome lights BTW!!!! Your the man Jeff

[dyezak]

Shiv, you need to tell Michael over there at ETS to get off his butt and get me a single turbo kit so I can put this procede to good use damnet.

[Robert@vishnu]

Michael is busy building all kinds of stuff. You can run our Single Turbo to match it with their 7" FMIC and it should be great!!!

Originally Posted by dyezak

Shiv, you need to tell Michael over there at ETS to get off his butt and get me a single turbo kit so I can put this procede to good use damnet.

[Tiago@VRSF]

Originally Posted by Jeff@topgearsolutions

This was already explained and why its better to do it the right way.

Just caught it. I definitely love the fact that you have more control with the two individual banks but people have obviously been tuning single bank 6 cylinder turbo'd motors for quite some time now. Even the N55 uses a single set of o2's for all 6 cylinders.

Then again, if it ain't broke, don't fix it No sense in making a bunch of changes if the dual bank setup isn't going to effect reliability of the sensors, especially if you retain the control.

[ajsalida]

Originally Posted by Jeff@topgearsolutions

This was already explained and why its better to do it the right way.

Well yes but I doubt BMW did it the "wrong" way on the N55. My limited understanding of these systems is, if you know exhaust path length as a function of relevant parameters (boost, flow, rpm etc.), then you can time-window the sensor output readings and infer each cylinder's individual AFR pulse as it comes out of the collector. At least some of the more advanced NA engines were doing this last time I looked. I imagine it's way more complicated on a turbo.

I would guess BMW upgraded processor, algorithms, and/or sensor capability on the N55 vs N54 DME, so eliminating one lambda sensor made sense, while still being able to do fuel trim for each cylinder within some spec. Maybe this is possible with major re-coding on the N54 but why bother when the existing system works so well?

[Jeff@TopGearSolutions]

Originally Posted by (-(ellblazer420

I was just about to quote that. You beat me to it. Thanks for the new dome lights BTW!!!! Your the man Jeff

Oh yea? You mean from HPB though.

Originally Posted by Tiago@VRSF

Just caught it. I definitely love the fact that you have more control with the two individual banks but people have obviously been tuning single bank 6 cylinder turbo'd motors for quite some time now. Even the N55 uses a single set of o2's for all 6 cylinders.

Then again, if it ain't broke, don't fix it No sense in making a bunch of changes if the dual bank setup isn't going to effect reliability of the sensors, especially if you retain the control.

Yes but its a MAF based system so I believe things change?

Originally Posted by ajsalida

Well yes but I doubt BMW did it the "wrong" way on the N55. My limited understanding of these systems is, if you know exhaust path length as a function of relevant parameters (boost, flow, rpm etc.), then you can time-window the sensor output readings and infer each cylinder's individual AFR pulse as it comes out of the collector. At least some of the more advanced NA engines were doing this last time I looked. I imagine it's way more complicated on a turbo.

I would guess BMW upgraded processor, algorithms, and/or sensor capability on the N55 vs N54 DME, so eliminating one lambda sensor made sense, while still being able to do fuel trim for each cylinder within some spec. Maybe this is possible with major re-coding on the N54 but why bother when the existing system works so well?

See above remark.

I think its only appropriate to commend the use of this safe tuning approach instead of trying to find loop holes, my .02 (Not saying N55 used loop holes btw).

[Tiago@VRSF]

Originally Posted by Jeff@topgearsolutions

Oh yea? You mean from HPB though.

Yes but its a MAF based system so I believe things change?

See above remark.

I think its only appropriate to commend the use of this safe tuning approach instead of trying to find loop holes, my .02 (Not saying N55 used loop holes btw).

I agree. I definitely think Shiv's got the right approach.

[ajsalida]

For all you control geeks out there:

"Estimation of Individual Cylinder Fuel Air Ratios from a Switching or Wide Range Oxygen Sensor for Engine Control and On-Board Diagnosis

http://papers.sae.org/2011-01-0710/

I did not know this was already a 2011 CARB requirement...

[Pe90X]

great stuff here!! cant wait til this is placed on the market..

[firechicken99]

Originally Posted by Pe90X

great stuff here!! cant wait til this is placed on the market..

Agreed, awesome to see that threads full of solid, non trolling, and informative information sharing still exist!