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Location:
Sydney
Registered:
January 2004
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Location:
On your mum!
Registered:
May 2002
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Re: Is this possible - telling a bad O2 sensor
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Tue, 11 January 2005 09:07
 
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the efi doesn't run by the 02 sensor. If at 2500rpm the voltage is oscillating I imagine that it is as a result of the engine running in closed loop - this is where the management will run the engine incrementally leaner until a certain point and then will track back to slightly rich and then again incrementally leaner and so on and so forth.
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Location:
Sydney
Registered:
January 2004
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Re: Is this possible - telling a bad O2 sensor
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Tue, 11 January 2005 09:26
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Yeah that's how I see it. I understand that much. But if it;s oscillating like that then it *should* be running close to 14.7 at that time. So if you put exhaust gas analyser on you should be seeing around 14.7:1. If not then the oxy sensor must be reading incorrectly right? I read somewhere it has ability to add or subtract 20% fuel based on 02 readings
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Location:
Wollongong
Registered:
November 2004
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Re: Is this possible - telling a bad O2 sensor
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Tue, 11 January 2005 09:36
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| HighRolla wrote on Tue, 11 January 2005 20:26 |
Yeah that's how I see it. I understand that much. But if it;s oscillating like that then it *should* be running close to 14.7 at that time. So if you put exhaust gas analyser on you should be seeing around 14.7:1. If not then the oxy sensor must be reading incorrectly right? I read somewhere it has ability to add or subtract 20% fuel based on 02 readings
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An N/A car will run 02 sensor closed loop to get back to 14.7, thats alls the standard O2 sensor will go to...
Turbo cars usually run in Open loop unless a 5V linear O2 sensor is installed...
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Location:
Sydney
Registered:
January 2004
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Re: Is this possible - telling a bad O2 sensor
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Tue, 11 January 2005 10:09
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I'm just saying if it is faulty is there a chance that it could be trying to get the fule mixture back to an incorrect level?
Most turbo cars still run a standard 02 sensor I believe...e.g skylines use same oxy sensor as a falcon
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Location:
Wollongong
Registered:
November 2004
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Re: Is this possible - telling a bad O2 sensor
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Tue, 11 January 2005 10:23
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The turbo cars might do a "fudge" so that it won't lean the engine out... Because I know, soarers, skylines, S13s.. They all run insanely rich...
As for the O2 sensor...
1) It will send no signal, and stuff the ECU around (Make it run wierd map)
2) if it sends the incorrect value, it will make the car extraordinarily rich or lean...
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Registered:
May 2004
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Re: Is this possible - telling a bad O2 sensor
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Tue, 11 January 2005 11:04
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I mean it should be reading .45v when there is a certain oxygen content
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On the contrary, if your O2 sensor does not oscillate, then you can assume that it is fucked.
An O2 sensor, as a generalisation should fluctuate between 0.1V and 0.9V.
As a basic rule of thumb, O2 sensors are merely mixture trimmers attempting to reach your stoichiometric ratio of 14.7:1.
"Most" cars will run OK with the O2 sensor disconnected, but then again most cars will illuminate the "check engine" lamp if this is disconnected.
Also keep in mind that your O2 sensor only detects the amount of oxygen remaining in the exhaust gas, expressed to the ECU as a percentage of your exhaust gas as a whole.... I hope that made sense.
However, don't be fooled by your stoichiometric ratio of 14.7:1 as keeping you out of trouble. A high performance engine can run in and closely around the perfect "14.7:1", but on the other end your HC's (hydrocarbons) and CO's (carbon monoxides)can be at a highly unacceptable level.
In oreder to answer your question as to whether an O2 sensor can give a false reading,..ofcourse it can. Especially if the readings are not constantly fluctuating.
But generally if your O2 sensor is faulty, it will be one or possibly both of two reasons.
You have contaminated your Titanium or Zirconia composite O2 sensor, or your wiring has failed you.
With contamination, you usually will not get a fluctuating reading, or an incorrect reading.
If there is a wiring problem, your ECU will usually recognise a "no activity" situation, which the ECU will usually log a code!
A "no activity" situation can also occur on a contaminated O2 sensor!
Hope this helped out in some way!
[Updated on: Tue, 11 January 2005 11:10]
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Location:
Brisbane
Registered:
February 2003
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Re: Is this possible - telling a bad O2 sensor
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Tue, 11 January 2005 11:27
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just an aditional note about O2 sensors - the 'narrow band' type found in most cars will either indicate lean, stoich or rich. The variation from 0.45V will not indicate how from off stoich the gasses are.
'Wideband' sensors will indicate the actual amount of O2 found in the gas - but these guys (until recently) are very expensive and require a lot more electronics to control and use (e.g. you cant just replace a narrow band unit with a wideband).
Also, until an engine is at operating temps and the O2 sensor likewise is at proper temps it will not read correctly and any decent ECu will ignore the O2 readings until then.
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Location:
Sydney
Registered:
January 2004
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Re: Is this possible - telling a bad O2 sensor
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Tue, 11 January 2005 11:37
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Thanks guys. Yeah the 02 is flutctuating between about 0.1v and 0.9 volts. So I guess it is probably ok.
Don't know why the fuel consumption isn't better then
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Location:
Brisbane
Registered:
February 2003
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Re: Is this possible - telling a bad O2 sensor
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Tue, 11 January 2005 13:05
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maybe it's outside the engine?
rubber still good?
wheel/diff bearings OK?
brakes not dragging?
wheel alignment good?
aircon or other engine loads OK?
maybe it's running rich to counter the effect of something else?
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Location:
Sydney
Registered:
January 2004
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Location:
Wollongong
Registered:
November 2004
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Re: Is this possible - telling a bad O2 sensor
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Wed, 12 January 2005 05:13
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| thechuckster wrote on Tue, 11 January 2005 22:27 |
just an aditional note about O2 sensors - the 'narrow band' type found in most cars will either indicate lean, stoich or rich. The variation from 0.45V will not indicate how from off stoich the gasses are.
'Wideband' sensors will indicate the actual amount of O2 found in the gas - but these guys (until recently) are very expensive and require a lot more electronics to control and use (e.g. you cant just replace a narrow band unit with a wideband).
Also, until an engine is at operating temps and the O2 sensor likewise is at proper temps it will not read correctly and any decent ECu will ignore the O2 readings until then.
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On the note of prices...
My boss bought a wide band UEGO 5V O2 sensor to help tune customer cars...
$200 for the sensor...
Then it was $800 for the actual computer piece that transferred it into a proper signal that the ECU could use...
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Location:
Campbelltown, NSW
Registered:
November 2002
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Re: Is this possible - telling a bad O2 sensor
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Fri, 14 January 2005 23:37
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just out of curiosity how many kilometres are on the car???
and how many k's you getting to a tank.
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Location:
Sydney
Registered:
January 2004
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Re: Is this possible - telling a bad O2 sensor
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Sat, 15 January 2005 00:30
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Ok car is AE92 4AFE auto corolla. 220k kms and getting about 10-11L/100kms
I got a mechanic I know to wack it on the exhaust Gas analyser. Running about 15.1 A/F ratio at idle. Unburnt HC are about 140ppm. But when you give it a bit for a while and then back off the hC are up about 500ppm and increased CO meaning incomplete combustion. He reckons that it's covered a fair few clicks so might be down on compression a bit.
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Registered:
May 2004
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Re: Is this possible - telling a bad O2 sensor
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Sat, 15 January 2005 01:52
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In all honesty, with 200 000kms+ on the dial, I would not worry too much.
If the car is driving OK then only persue the matter if you are concerned.
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Is this possible - telling a bad O2 sensor
