[ferocity02]

For those of you who have installed DP's, is there any need to physically keep the rear O2 sensors installed? With them installed you will get cat efficiency codes, but these can be coded out so the SES light doesn't come on. However, if you physically remove the O2 sensors will it cause other codes that cannot be coded out?

[KeepRidingDirty]

Originally Posted by ferocity02

For those of you who have installed DP's, is there any need to physically keep the rear O2 sensors installed? With them installed you will get cat efficiency codes, but these can be coded out so the SES light doesn't come on. However, if you physically remove the O2 sensors will it cause other codes that cannot be coded out?

I think the light is cleared with Tunes/JB4. I think the reason people leave them in is because they affect the fuel trims eventually. I thought they just measure cat efficiency but I've been corrected by people with more knowledge than me on the subject.

[Tiago@VRSF]

You should definitely keep the rear o2's installed. The DME uses them for the fuel trims

[Jnat]

Originally Posted by Tiago@VRSF

You should definitely keep the rear o2's installed. The DME uses them for the fuel trims

THIS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[ferocity02]

Originally Posted by Tiago@VRSF

You should definitely keep the rear o2's installed. The DME uses them for the fuel trims

Okay. That is interesting to hear. Seems like most other vehicles only use the front O2 sensors for fuel trimming since the readings of the rear O2's is affected by the cats.

So how does not having cats affect the fuel trims? As far as the DME knows the cats are still there.

[Tiago@VRSF]

Going catless will not have a negative effect on performance. The DME knows they aren't there by the readings. The tunes don't delete the rear o2's, they simply remove the ability for the DME to complete the cat monitor readiness which eliminates the CEL.

[Mike@N54Tuning.com]

Originally Posted by ferocity02

For those of you who have installed DP's, is there any need to physically keep the rear O2 sensors installed? With them installed you will get cat efficiency codes, but these can be coded out so the SES light doesn't come on. However, if you physically remove the O2 sensors will it cause other codes that cannot be coded out?

You need them installed or you will cause a lot more problems then a simple CEL from no cats.

Mike

[AngelFarelli]

Originally Posted by Mike@N54Tuning.com

You need them installed or you will cause a lot more problems then a simple CEL from no cats.

Mike

Can you list proof that the downstream o2 sensor has any relation to a/f ratio fuel trim or ecu ?

[TiAgAu]

Originally Posted by AngelFarelli

Can you list proof that the downstream o2 sensor has any relation to a/f ratio fuel trim or ecu ?

Explained in detail https://www.youtube.com/watch?v=bmWjoudIOCk

[dpaul]

Originally Posted by AngelFarelli

Can you list proof that the downstream o2 sensor has any relation to a/f ratio fuel trim or ecu ?

The proof is that if you remove the post-cat sensors and regularly log DME data, you will see that the trims start to drift. AFRs are not being accurately reported and driveability issues occur. It doesn't happen overnight - it can take a while.

There are quite a few posts reporting this behavior. Not 100% of all posters have observed the trim drift but most do.

Explanation: the post-cat sensors are narrow-band and thus exhibit a very sharp transition in voltage output around lambda =1. That is, the voltage changes rapidly just above or just below. Meaning they don't accurate report small changes in AFR but very accurately report lambda =1 ("stoichiometric" regardless of fuel type). The pre-cat sensors, are wide-band which makes them useful for reporting minor difference in AFR around stoichiometric which is what you want for fine tuning the AFR. But as a necessary consequence, the pre-cat sensors exhibit relatively small voltage changes around lambda = 1. Meaning, they accurately report small changes in AFR but don't accurately report lambda = 1.

So the DME uses the post-cat sensors as a standard to accurately calibrate the output of pre-cat sensors at lambda =1. If you remove the post-cat sensors, things eventually drift out of calibration and you have problems.

[type-dRew]

Originally Posted by AngelFarelli

Can you list proof that the downstream o2 sensor has any relation to a/f ratio fuel trim or ecu ?

take them off and see for yourself

[trb1]

I ran ridiculously lean with a bad rear o2. If I reset adaptations i could drive for about 50-75 miles before it would start to lean out again. They affect long term trims. They have a trimming control system. If you remove them you’ll run into issues. Just turn off the cat codes with tuner pro.

[AngelFarelli]

Originally Posted by dpaul

The proof is that if you remove the post-cat sensors and regularly log DME data, you will see that the trims start to drift. AFRs are not being accurately reported and driveability issues occur. It doesn't happen overnight - it can take a while.

There are quite a few posts reporting this behavior. Not 100% of all posters have observed the trim drift but most do.

Explanation: the post-cat sensors are narrow-band and thus exhibit a very sharp transition in voltage output around lambda =1. That is, the voltage changes rapidly just above or just below. Meaning they don't accurate report small changes in AFR but very accurately report lambda =1 ("stoichiometric" regardless of fuel type). The pre-cat sensors, are wide-band which makes them useful for reporting minor difference in AFR around stoichiometric which is what you want for fine tuning the AFR. But as a necessary consequence, the pre-cat sensors exhibit relatively small voltage changes around lambda = 1. Meaning, they accurately report small changes in AFR but don't accurately report lambda = 1.

So the DME uses the post-cat sensors as a standard to accurately calibrate the output of pre-cat sensors at lambda =1. If you remove the post-cat sensors, things eventually drift out of calibration and you have problems.

Thank you so much. This is the type of answer I am looking for. Every answer I found on the forum more of less just says yeah without posting data sheets to prove long term fuel trim drift !! Makes me mad. I also read about the wide and narrow band explanation which led me to believe that the o2 sensor does play a roll. I was mainly looking for links to this proclaimed data however I think I have my answer !

Quote:

The tunes don't delete the rear o2's, they simply remove the ability for the DME to complete the cat monitor readiness which eliminates the CEL.

[AngelFarelli]

My original question was why o2 spacers like the fabspeed with mini catalytic converters in them won't work on these cars?
I guess the answer to that ,as far as I know, is not completely known because no one has bought one and logged their long term fuel trim?? Does anyone know if this has been done successfully? https://www.fabspeed.com/universal-o...verter-single/

[dpaul]

Originally Posted by AngelFarelli

My original question was why o2 spacers like the fabspeed with mini catalytic converters in them won't work on these cars?
I guess the answer to that ,as far as I know, is not completely known because no one has bought one and logged their long term fuel trim?? Does anyone know if this has been done successfully? https://www.fabspeed.com/universal-o...verter-single/

I'm unfamiliar with those devices. They do not appear to be popular among E9x owners.

But here's what a Fabspeed rep had to say about their installation on N55 engines of the F30 forum:

"Phil from Fabspeed here.
The catted O2 spacers are a great solution for this issue. There are a couple drawbacks to them though. If you actually have a sniffer test these will not help you pass. If it is an ecu test these can help "trick" it. They are however very tempermental sometimes you have to have them up stream and sometimes pointed downstream. They have about a 60/40 chance of working as well. Please let me know if you have any other questions."

I'm guessing the "60/40" chance of working is why you don't hear much about them.

Just to be clear, this "60/40" chance of working is to fulfil the primary function of spoofing the DME into thinking that cats are still present. Nothing to do with long term trims.

[type-dRew]

Speaking directly from when i attempted to use a spacer on my old turbo hyundai, my fuel trims were completely out of whack, I had no idea why. I eventually removed the sensor completely and things got way worse.

At that point I installed the sensor again, with no spacer and the car ran perfect.

Dont use spacers on cars that have the appropriate software capability of turning off the codes. Or just live with the CEL on the dash. No money spent and a light is better than money spent and ruining the way the car functions.

If this car is anything like my old hyundai, and it is, removing or spacing the rear o2s, anything that lies to the dme about post cat o2 function, is going to fuck up the fuel trims.

[AngelFarelli]

Yeah I read the 60/40 thing last night and gave up on the thing but I'm still not giving up on this! There has to be a mechanical answer even if it isn't the fabspeed! I know the tune method is practically the same price with extra added benefits.
I watched that video and it definitely helped a lot thank you.
I have heard however you can tap into the 4 wires on the o2 sensor without going the tune method?? Is this true ? And yes I know you can run stock boost while still having the cel eliminating function with tune method but still feel unsatisfied. If the dme is made to work with a catalytic converter than taking it out will mess with fuel trim reguardless of cel correct? I think that is reall my big question

[AngelFarelli]

I think I might be misunderstood but the narrow band downstream o2 sensor can tell really well whether or not you are lean or rich because it's Volts read 0-1 volts depending on rich 11.8:1 afr giving 1 volt, or lean 17.6:1 afr giving 0 volts.
This differs from the wide band o2 sensor which is better at measuring even more lean/rich afr. This is measured by current in mA either negative reading stating there is a rich condition up to afr of 5:1 or measuring positive stating a lean condition up to afr of 20:1.

[Jeff@TopGearSolutions]

Originally Posted by AngelFarelli

Yeah I read the 60/40 thing last night and gave up on the thing but I'm still not giving up on this! There has to be a mechanical answer even if it isn't the fabspeed! I know the tune method is practically the same price with extra added benefits.
I watched that video and it definitely helped a lot thank you.
I have heard however you can tap into the 4 wires on the o2 sensor without going the tune method?? Is this true ? And yes I know you can run stock boost while still having the cel eliminating function with tune method but still feel unsatisfied. If the dme is made to work with a catalytic converter than taking it out will mess with fuel trim reguardless of cel correct? I think that is reall my big question

To answer your last question, the DME does not "work with the catalytic converter". It works with the O2 sensors, strictly. The O2 sensors control the fueling and yes the rears are important on this platform. Hope this helps.