Position of oxygen sensor in exhaust

[patprimmer]

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?

Regards
Pat
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[NickJ67]

Interesting. Hence this warning from the LC-1 manual

"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

 

[WGJ]

The ceramic thimble in any oxygen sensor is fine when installed and operated in the way that manufacturers advise.
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