Position of oxygen sensor in exhaust
Position of oxygen sensor in exhaust
(OP)
I have become involve in tuning older Hondas by replacing a chip in the ECU with a rewritable chip or with a real time emulator where fuel and ignitions maps and quite a few other parameters can be altered to re-tune to optimise a different set of priorities and/or for significant changes to the engine.
One of the main feedbacks is reading a wide band oxygen sensor as a basis for altering fuel maps.
Some oxygen sensors have very good life, but others consistently fail within a few months, first sign being erratic or inaccurate readings.
I am suspecting that they are either running to cold and loading up with carbon or in some cases running to hot and being damaged by heat. All the cars involved have had turbochargers added and most are used exclusively for competition, but some are dual purpose or even various types of competition from autocross to hill climb to drag racing to circuit racing. One guy in Sweden even races on ice at times.
My questions.
Does an oxygen sensor need to be held in a specified temperature range to be accurate and/or durable.
If so what happens when to cold.
What happens when to hot.
Is moving the sensor closer or further from the turbo a legitimate way to control operating temperature of the oxygen sensor?
One of the main feedbacks is reading a wide band oxygen sensor as a basis for altering fuel maps.
Some oxygen sensors have very good life, but others consistently fail within a few months, first sign being erratic or inaccurate readings.
I am suspecting that they are either running to cold and loading up with carbon or in some cases running to hot and being damaged by heat. All the cars involved have had turbochargers added and most are used exclusively for competition, but some are dual purpose or even various types of competition from autocross to hill climb to drag racing to circuit racing. One guy in Sweden even races on ice at times.
My questions.
Does an oxygen sensor need to be held in a specified temperature range to be accurate and/or durable.
If so what happens when to cold.
What happens when to hot.
Is moving the sensor closer or further from the turbo a legitimate way to control operating temperature of the oxygen sensor?
Regards
Pat
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RE: Position of oxygen sensor in exhaust
There's more leeway on the hot side, but they're not bullet-proof. If you're running FI, my guess is you're also running pretty rich (typical tuning)... that leads to carbon build-up.
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Position of oxygen sensor in exhaust
I would expect enough heat would burn the carbon off. I just wonder how much they will take and what indicates to much. Do you look to get heat marks like the metal body of a spark plug? If not, do you move it closer to the turbo.
Regards
Pat
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RE: Position of oxygen sensor in exhaust
Anything that increases the sustained EGT at the O2 sensor, e.g. rich mixture and/or adding a turbo, has to shorten its life.
I'd start by moving the 02 sensor farther downstream, by many diameters for a competition engine, by a few diameters for a hotted up street engine.
... but all of that is just a WAG.
Mike Halloran
Pembroke Pines, FL, USA
RE: Position of oxygen sensor in exhaust
I know they can get covered with carbon and stop working and can then be carefully cleaned with an oxy torch, just like a spark plug fouled with carbon. I have to admit that I only did that to an old single wire narrow band unheated one.
Regards
Pat
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RE: Position of oxygen sensor in exhaust
Are the ones used in competition, or even the street ones, using a fuel other than regular unleaded pump gas? Running any additives? There are quite a few things that can foul a sensor besides just running rich.
RE: Position of oxygen sensor in exhaust
How much power are we talking about here? I would shoot more for 12-12.5 AF under heavy load.
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Position of oxygen sensor in exhaust
It is the 500hp engine that is getting real short life, like 15 or 20 1/4 mile runs.
Regards
Pat
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RE: Position of oxygen sensor in exhaust
I'm kinda old and don't know much about all this new fangled stuff, give me a set of Webers or SU's and "I'm there!"
Rod-----File this under WAG, too.
RE: Position of oxygen sensor in exhaust
I found a recommended temperature range and I will try a few runs with some EGT measurements in a few spots and aim for the hottest spot that never exceeds spec with a small safety margin for variations in ambient.
Regards
Pat
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RE: Position of oxygen sensor in exhaust
Does the sensor recover on its own after it has had a chance to cool down, or is it essentially fooked at that point? A good high-temp sensor should get you into the 400-450C range, but with high-HP, FI apps you can reach that limit pretty quick. Watching the turbo housing turn cherry red tells you something about the possible EGTs :-/
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Position of oxygen sensor in exhaust
I am not sure how they handle a:f when the blow off valve operates, however these are MAP sensor not MAF sensor based systems.
I have not had them in my hand. My involvement to date has been at an advice level.
The owner has found a set of instructions and specs that give max and minimum temperatures.
He decided they are cheap and will just keep replacing them short term. I have advised him to collect some EGT data at different spots and compare to min max specks for the sensor.
Until I hear back, as far as I am concerned this is now closed, at least until I am installing my own.
I certainly would like to see their data before I install my own.
Regards
Pat
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RE: Position of oxygen sensor in exhaust
You may have seen this before but seems to be some good info regarding installation of the sensor (pages 6 - 8) and includes a warning about temperatures on page 8 (not to exceed 500ºC at the hex) even a little sketch of a possible heatsink.
http:
These LC-1 kits use a Bosch sensor.
Regards
Nick
RE: Position of oxygen sensor in exhaust
I should have taken the advice I often hand out. RTFM. I did not have a manual, but should have thought to search for one.
Regards
Pat
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RE: Position of oxygen sensor in exhaust
Been a long time chap...
I would venture that your problem is not one of heat, per se, more so moisture.
Basically, after a cold start, most OEMs delay providing the O2 sensor with full heating power. This delay is so that there is no risk of condensation forming on the 'relatively' hotter ceramic contained within the sensor - its called the 'Dewpoint Delay'. If it were to occur then cracking & failure is highly likely
My recommendation would be to delay switching on the sensor heater for a couple of minutes to ensure that things are nicely warmed through.
Hope that's of some help...
MS
RE: Position of oxygen sensor in exhaust
Thanks for the input. Original problem was solved by surprise surprise, reading the manual,however your advice sounds very interesting as ome have a very short life and I expect with hot rodded ECUs they may deliberately or accidentally disabled a sensor warm up dry out mode. We have a similar problem with some heater elements on injection moulding machines and a two phase warm up greatly extends heater element life.
Regards
Pat
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RE: Position of oxygen sensor in exhaust
???? I don't doubt the delay, just the logic. Condensation happens when warm gasses encounter colder surfaces.
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Position of oxygen sensor in exhaust
The condensation doesn't form due to the ceramic element being hotter - the presence of liquid phase water on the cold exhaust walls puts the element at risk of thermal shock, should any of it find its way on to the element. A risk that isn't present when everything is up to temp.
MS
RE: Position of oxygen sensor in exhaust
Norm
RE: Position of oxygen sensor in exhaust
Regards
Pat
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RE: Position of oxygen sensor in exhaust
"It is NOT a good idea to connect the LC-1 permanently to 12V and switch it on with a separate switch before the vehicle is started. Depending on the climate and the sensor position in the exhaust, condensation water can form in the exhaust pipes. This condensation water could then be blown by the exhaust stream against the hot sensor when the car is started. The resulting heat shock can permanently damage the sensor."
They also caution (in capitals no less) against leaving an unpowered sensor in the exhaust stream.
"WHEN INSTALLED IN THE EXHAUST, THE OXYGEN SENSOR
MUST BE CONNECTED AND OPERATING WITH THE LC-1
WHENEVER THE CAR IS RUNNING. AN UN-POWERED OXYGEN
SENSOR WILL BE DAMAGED WHEN EXPOSED TO EXHAUST GAS"
Some minor conflict between these two......
I guess a significant part of the battle is to mount the sensor close enough to the engine that condensation is unlikely, though not so hot as to melt it......
Mostly they last remarkably well in OEM applications so they must be pretty tough! My two aftermarket applications are doing ok too - one up to something like 20K miles now.
Nick
RE: Position of oxygen sensor in exhaust
Engine and ancillary components in production cars are expected to last a minimum of 100k miles (more like 150k these days) - this is to keep automotive warranty costs down and to provide the customer with the right, satisfactory, ownership experiences.
Hence, following the OE sensor manufacturer's nstallation advice and operating procedures will ensure that the part will have a minimum reliable operational life.
Heater voltages - 5 or 12v and applied as stipulated (e.g. PWM control)
Sensor connection - electrcally loaded as the manufacturer stipulates (i.e. the resistance/impedance that the sensor connects to in the ECM or hego interface module)
Contact resistances - Low, very low. Recommendation may be for gold on the sensor element connection.
Bill