Readiness - Catalyst

carabuser

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I often see mention of people struggling to pass vehicle inspections over in the US specifically the catalyst readiness status.

I have no idea how things work over there so excuse the possibly dumb question, but would setting the status of the catalyst monitor to "Not Available" allow people to pass without needing a "DP Fix"?

Just been playing around with diagnostic routines related to the primary cats as I have them removed and wanted to get rid of any background routines related to them since they will invariably fail. I found a simple binary selector that lets you disable whatever diagnostic routines you want. I turned off the one for catalyst monitoring and have been driving around without any issues for a while, I noticed as a side effect the readiness state now states "Not Avail." when scanned.
 
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corbanistan

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Jul 26, 2021
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I often see mention of people struggling to pass vehicle inspections over in the US specifically the catalyst readiness status.

I have no idea how things work over there so excuse the possibly dumb question, but would setting the status of the catalyst monitor to "Not Available" allow people to pass without needing a "DP Fix"?

Just been playing around with diagnostic routines related to the primary cats as I have them removed and wanted to get rid of any background routines related to them since they will invariably fail. I found a simple binary selector that lets you disable whatever diagnostic routines you want. I turned off the one for catalyst monitoring and have been driving around without any issues for a while, I noticed as a side effect the readiness state now states "Not Avail." when scanned.
Any update on this carabuser? I'm having oscillations at idle due to the routine on catless. What's the parameter called? I'll go ahead and find it for I8A0S.
 

carabuser

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There's a few different ones and they vary a lot by ROM. I don't think it's just the catalyst one that messes with lambda as I've seen it still occur on cars where that's turned off.

You can try C_AMP_MIN_CAT first, set that to something like 10PSI, should prevent it ever starting.
 

KClemente

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If you don't care for the catalyst readiness, you can also go ahead and disable catalyst purge too while you're at it
 

carabuser

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If you don't care for the catalyst readiness, you can also go ahead and disable catalyst purge too while you're at it
Yes cat purge can go. That's an enrichment the DME does when getting back onto throttle after overrun fuel cut. It's supposed to flush air out of the cats to gets the O2s reading correctly but if you have catless downpipes it's pointless.

I also noticed there's a desulfation routine but I don't know if that's useful for the secondary cats or if it's just intended for the primaries.
 

corbanistan

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Yeah I remember looking into this stuff in the damos weeks ago but didn't touch it since I personally hadn't heard of anyone else messing with those tables yet. I have a good reason to now, thanks gents
 

corbanistan

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Yes cat purge can go. That's an enrichment the DME does when getting back onto throttle after overrun fuel cut. It's supposed to flush air out of the cats to gets the O2s reading correctly but if you have catless downpipes it's pointless.

I also noticed there's a desulfation routine but I don't know if that's useful for the secondary cats or if it's just intended for the primaries.
Noticed on a different forum you mentioned exhaust pressure tables taking into account cats being there on stock cars. Are those tables something you've experimented with to adjust for catless?
 

corbanistan

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Alright so I've defined a few tables:
c_amp_min_cat which @carabuser pointed out. That can be used to raise the minimum ambient temp required to start cat monitoring (hence disabling it).
c_n_max_cat_purge which can be used to disable cat purge by lowering RPM to below idle.
c_state_inh_nt_so2p_req, this I'm not positive but looks to disable desulfation if set to 1.
Am I missing anything?

EDIT: Looks like LC_CAT_PURGE_INH can also be used to disable cat purge.
 

KClemente

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Nov 26, 2019
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Alright so I've defined a few tables:
c_amp_min_cat which @carabuser pointed out. That can be used to raise the minimum ambient temp required to start cat monitoring (hence disabling it).
c_n_max_cat_purge which can be used to disable cat purge by lowering RPM to below idle.
c_state_inh_nt_so2p_req, this I'm not positive but looks to disable desulfation if set to 1.
Am I missing anything?

EDIT: Looks like LC_CAT_PURGE_INH can also be used to disable cat purge.
We do not have NOx sensors installed so anything in the NOx desulfation tables will not be of any use. I believe that is mostly meant and designed for N53's with stratified fueling
 

studio54

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Dec 20, 2021
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Alright so I've defined a few tables:
c_amp_min_cat which @carabuser pointed out. That can be used to raise the minimum ambient temp required to start cat monitoring (hence disabling it).
c_n_max_cat_purge which can be used to disable cat purge by lowering RPM to below idle.
c_state_inh_nt_so2p_req, this I'm not positive but looks to disable desulfation if set to 1.
Am I missing anything?

EDIT: Looks like LC_CAT_PURGE_INH can also be used to disable cat purge.
That's great !

Any testing yet ?

I also have the Helix oscillation (13.8 / 15.1 bouncing from bank 1 to 2) on my AFR at idle and at low load/rpm aswell ( I8A0S / catless ), as discussed a lot recently with CarAbuser, i would like to smooth it for my emissions test.
 
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corbanistan

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So I've tried disabling C_AMP_MIN_CAT as CarAbuser suggested. Didn't solve the oscillations but it did remove cat shadow codes from appearing, which was useful. Haven't had time to try disabling cat purge yet. I've put most of my time recently into improving my tune. There's got to be something else in there to fix the idle AFRs. I'll take another look tonight at some point.
 
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corbanistan

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Jul 26, 2021
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Ok so I did a quick read on the catalyst diag functions of our ECUs. Looks like there are multiple tables that relate to this AFR issue. What it looks like the ECU is doing is comparing sensor values from pre and post cat to determine efficiency, but since we're catless the routine fails and continues to run. There's a whole page in the docs on how this works. Anyways, there's a variable C_N_32_CAT_DIAG_DEAC "Engine speed threshold to deactivate catalyst diagnosis to save ECU performance". I will set that to something low and report back with my findings soon. I've already found it in I8A0S.

This may take some iterative trial and error but we'll get it sooner or later...
 

corbanistan

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There's a routine the ECU runs called "Lambda Stimulation". Looks like it's another catalyst efficiency thing. There seems to be a few ways to disable this.
 
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studio54

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Dec 20, 2021
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Ok so I did a quick read on the catalyst diag functions of our ECUs. Looks like there are multiple tables that relate to this AFR issue. What it looks like the ECU is doing is comparing sensor values from pre and post cat to determine efficiency, but since we're catless the routine fails and continues to run. There's a whole page in the docs on how this works. Anyways, there's a variable C_N_32_CAT_DIAG_DEAC "Engine speed threshold to deactivate catalyst diagnosis to save ECU performance". I will set that to something low and report back with my findings soon. I've already found it in I8A0S.

This may take some iterative trial and error but we'll get it sooner or later...

What is the default value of C_N_32_CAT_DIAG_DEAC ? Is it higher than 2650 rpm?

When i logged my accelerated idle to simulate the emission test, up to 2650 rpm at neutral, AFR were still bouncing.
 

carabuser

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What is the default value of C_N_32_CAT_DIAG_DEAC ? Is it higher than 2650 rpm?

When i logged my accelerated idle to simulate the emission test, up to 2650 rpm at neutral, AFR were still bouncing.
There's quite a few things that could cause the problem. I managed to disable all the ones that are active during driving on my car but never looked at the idle ones.

Try changing this value to 1774, conversion is X*0.0625:
1640181298288.png
 
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carabuser

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Also you can unzip this file and place into the MHD root folder in android. This will let you monitor 3 extra channels related to catalyst functions.

Add these to a log when the lambda is oscillating and it should help pinpoint what routine causes it.
 

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