Should last forever that way. 
Non Stoich O2 Switching ?!
Thread Starter
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Joined: Aug 2003
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From: England UK
Non Stoich O2 Switching ?! I have a pair of Bosch 13111's fitted in the front O2 positions. My WB sensor is fitted after the cat on the drivers side.
The car failed emmisions, it was running lean @ 1.04 lambda, limit was 1.03. I put this down to a possible exhaust leak towards the rear end of the car. My WB guage was saying AFR was okay. At this point I was running in OL. When it weas in CL it was 15.5AFR, or reading 1.17 Lambda. Thats like 17% too lean.
So I looked into this further and done some logging.
The front O2's were replaced 5 months ago, approx 3000miles ago.
The WB sensor (Bosch) was replaced 2 months ago.
When driving with slight acceleration I can feel something isn't right. Not put it under load as I know running lean isn't good. My WB guage is saying 15.5 ish AFR and I can seel it occilating between 15 and 16AFR. I would expect to see it occilatiing around Stoich.
So what this means is either my WB is reading lean or my O2's are thinking things are right, and taking away fuel making me run lean which explans the bucking.
I always thought NB O2's could only ossolate around Stoich. When they go wrong the flat line (is that true)?
Either was my WB it telling my my O2's are not right. But who do I beleive?
Below is a screen capture of the readings. WB is at the top, NB's are on the 3rd graph.
Also look at the Fuel trims , one side is 4% different to the other.
Do I need to buy new NB's?
The car failed emmisions, it was running lean @ 1.04 lambda, limit was 1.03. I put this down to a possible exhaust leak towards the rear end of the car. My WB guage was saying AFR was okay. At this point I was running in OL. When it weas in CL it was 15.5AFR, or reading 1.17 Lambda. Thats like 17% too lean.
So I looked into this further and done some logging.
The front O2's were replaced 5 months ago, approx 3000miles ago.
The WB sensor (Bosch) was replaced 2 months ago.
When driving with slight acceleration I can feel something isn't right. Not put it under load as I know running lean isn't good. My WB guage is saying 15.5 ish AFR and I can seel it occilating between 15 and 16AFR. I would expect to see it occilatiing around Stoich.
So what this means is either my WB is reading lean or my O2's are thinking things are right, and taking away fuel making me run lean which explans the bucking.
I always thought NB O2's could only ossolate around Stoich. When they go wrong the flat line (is that true)?
Either was my WB it telling my my O2's are not right. But who do I beleive?
Below is a screen capture of the readings. WB is at the top, NB's are on the 3rd graph.
Also look at the Fuel trims , one side is 4% different to the other.
Do I need to buy new NB's?
Last edited by RedWS6 00; Apr 6, 2008 at 03:07 PM.
You have the ability to bend the O2 switchpoint, the threshold
has some influence on the "center" AFR though this is not at all
characterized. The stock tune uses about 350mV for most of it
and 450-500mV is considered the "stoich" point. If you are too
lean then might bump these values.
You might want to look at the wideband with both minimum and
maximum filtering time-constants. If the long-term is where you
want it but the short term is all over the road, you may want to
play with proportional fueling values to reduce how far it swings
from center and how long you spend at outlier fuel positions as
a result. There are options to use, or not, proportional fueling
at idle. If you don't then idle fueling may drift slowly in and out
as the ST/LTFTs then have the only way of making the closed loop
feedback, much slower.
has some influence on the "center" AFR though this is not at all
characterized. The stock tune uses about 350mV for most of it
and 450-500mV is considered the "stoich" point. If you are too
lean then might bump these values.
You might want to look at the wideband with both minimum and
maximum filtering time-constants. If the long-term is where you
want it but the short term is all over the road, you may want to
play with proportional fueling values to reduce how far it swings
from center and how long you spend at outlier fuel positions as
a result. There are options to use, or not, proportional fueling
at idle. If you don't then idle fueling may drift slowly in and out
as the ST/LTFTs then have the only way of making the closed loop
feedback, much slower.
Thread Starter
TECH Resident
Joined: Aug 2003
Posts: 970
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From: England UK
Thanks for the info.
The idle looks great, the WB reads 14.6 / 14.7 on idle
When driving and ST FT are zero, the LT FT's read -10 on one bank and -5 on the other bank.
So the Fuel trims are trying to take fuel away. But i think the O2's are reading wrong or its my WideBand reading wrong.
The Narrow Band O2's are switching around 500mV which is great. Thats what I want, but when they are switching around this the WB is reading 15 to 16 AFR. This is way too lean.
So, the NB O2's are either reading too rich or my WideBand is reading too lean. The two reading just done tie up. When the NB O2's are between saw 400mW and 600mW I should see a variation on the WideBand around 14.7, but its more like 15.5.
I dont know what sensors to trust. One of them is wrong.
When NB O2's get dirty do they just switch slower? what about the heater element? if there is a fuse I'll check that in my lunch break. I know NB O2's are meant to switch around 14.6 AFR but is there anyway they can switch around 15:5AFR is they are faulty? I'm thinking perhaps some wire got hot from the exhaust creating less resistance to +V, reading higher, so then it take away fuel making it read lean on the WB's.
The idle looks great, the WB reads 14.6 / 14.7 on idle
When driving and ST FT are zero, the LT FT's read -10 on one bank and -5 on the other bank.
So the Fuel trims are trying to take fuel away. But i think the O2's are reading wrong or its my WideBand reading wrong.
The Narrow Band O2's are switching around 500mV which is great. Thats what I want, but when they are switching around this the WB is reading 15 to 16 AFR. This is way too lean.
So, the NB O2's are either reading too rich or my WideBand is reading too lean. The two reading just done tie up. When the NB O2's are between saw 400mW and 600mW I should see a variation on the WideBand around 14.7, but its more like 15.5.
I dont know what sensors to trust. One of them is wrong.
When NB O2's get dirty do they just switch slower? what about the heater element? if there is a fuse I'll check that in my lunch break. I know NB O2's are meant to switch around 14.6 AFR but is there anyway they can switch around 15:5AFR is they are faulty? I'm thinking perhaps some wire got hot from the exhaust creating less resistance to +V, reading higher, so then it take away fuel making it read lean on the WB's.
Thread Starter
TECH Resident
Joined: Aug 2003
Posts: 970
Likes: 4
From: England UK
A Month Ago
A month ago the O2's were switching around 14.7 on the WideBand.
Two Weeks Ago
I went into OL for a couple of weeks to tune the VE via WB, not a lot of changes just minor tweaks. However did do a high speed WOT. Was over 5000rpm for about 2 mins. Cats put back in (getting ready for emmisions).
One Week Ago
Now ready for the emissions test I go back to Closed Loop. Where ever i drive i can see occilation on the Wideband, this is great I means the fuel trims are tweaking. So i give it 100 miles. But this occilation is around 15:5 AFR according to the WB.
Failed the emmisions test for being too lean. The emmisions test is at 3500RPM parked. This was located at 20kpa (MAP) my fuel trims wernt enabled until 35kpa, which I've corrected now. Seems silly having an emmisions test in an area you don't drive in.
Anyway, even in the driving area its still reading lean on the WB.
It seems to have happened after the high speed run, I wonder is oil got burnt and damaged the sensors, perhaps it just damaged the Wideband sensor, but when i accelerate it hesitates and worse the higher the number on the WB, so I'm starting to think the WB is correct, but then that would mean the NarrowBand O2's are incorrect. I dont know
, I'm going round in circles here.
The WB is after the cats now, most of the year i run with no cats. It cant be the cats making the WB read lean, as if it makes it read that inaccurate why do dynos read from the exhaust exit at the back after the cats.
A month ago the O2's were switching around 14.7 on the WideBand.
Two Weeks Ago
I went into OL for a couple of weeks to tune the VE via WB, not a lot of changes just minor tweaks. However did do a high speed WOT. Was over 5000rpm for about 2 mins. Cats put back in (getting ready for emmisions).
One Week Ago
Now ready for the emissions test I go back to Closed Loop. Where ever i drive i can see occilation on the Wideband, this is great I means the fuel trims are tweaking. So i give it 100 miles. But this occilation is around 15:5 AFR according to the WB.
Failed the emmisions test for being too lean. The emmisions test is at 3500RPM parked. This was located at 20kpa (MAP) my fuel trims wernt enabled until 35kpa, which I've corrected now. Seems silly having an emmisions test in an area you don't drive in.
Anyway, even in the driving area its still reading lean on the WB.
It seems to have happened after the high speed run, I wonder is oil got burnt and damaged the sensors, perhaps it just damaged the Wideband sensor, but when i accelerate it hesitates and worse the higher the number on the WB, so I'm starting to think the WB is correct, but then that would mean the NarrowBand O2's are incorrect. I dont know
, I'm going round in circles here.The WB is after the cats now, most of the year i run with no cats. It cant be the cats making the WB read lean, as if it makes it read that inaccurate why do dynos read from the exhaust exit at the back after the cats.
Last edited by RedWS6 00; Apr 7, 2008 at 05:20 AM.
Thread Starter
TECH Resident
Joined: Aug 2003
Posts: 970
Likes: 4
From: England UK
Looking at some logs a couple of months ago, the O2's were occilating around 14.7
Switching speed is similar to before, I just think they have got a bit coked up. Gonna check wiring in case of melted wires.
Can you clean these sensors, a mechanic said just put some brake cleaner on them, would that be good advice?
Switching speed is similar to before, I just think they have got a bit coked up. Gonna check wiring in case of melted wires.
Can you clean these sensors, a mechanic said just put some brake cleaner on them, would that be good advice?
Thread Starter
TECH Resident
Joined: Aug 2003
Posts: 970
Likes: 4
From: England UK
Problem solved, replaced both front O2's.
The old ones were only 4 or 5 months old (Bosch 13111's). They seemed to be switching high and low slower than when they were new. Also they seemed to think Lambda was 15.5 ish. Hence running very lean.
Eventually before I change them one of them flat lined at 0mV.
Changed them last night, took the car for emissions test and it went through first time.
The new ones are also Bosch 13111's.
Not sure why they failed so quick, but all okay now and road legal once again
The old ones were only 4 or 5 months old (Bosch 13111's). They seemed to be switching high and low slower than when they were new. Also they seemed to think Lambda was 15.5 ish. Hence running very lean.
Eventually before I change them one of them flat lined at 0mV.
Changed them last night, took the car for emissions test and it went through first time.
The new ones are also Bosch 13111's.
Not sure why they failed so quick, but all okay now and road legal once again
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