Transport delay time constant

[4wheelinls1]

Whats the transport time constant, used to only seeing transport delay.

[15PSI]

Here is a snippet from the patent: A time constant of the oxygen sensor is calculated as a function of the first and second limit cycle periods and compared to a maximum response rate.

The link:https://www.google.ch/patents/US5305727

I will let one of the more experienced tuners on the forum explain this in layman's terms....

[murfie]

The transport delay is basically the length of time the air fuel mixture leaves the combustion chamber and reaches the sensor. This is effected by changing different headers that place the sensor closer or further from the combustion chamber.

There is also a response delay that oxygen sensors have due to the way they operate as a buffered system.

Regulations require that these sensors have a monitoring system in place. This is usually what causes the check engine light to come on in higher mileage Honda's and Toyota's. The codes are "catalytic inefficacy" and usually turn out to be a bad sensor. The way they are usually monitored requires the engine to go into open loop mode(ecu ignores sensors and runs off tables) as the sensors are being checked. This is why you can clear the code and it doesn't return for a few thousand miles until the next sensor check. This also can cause the engine to run a nonstoich afr for a short period, usually rich.

What Ford has done is take advantage of the inherent response delay in oxygen sensors in order to monitor them even while they are in closed loop mode(controling the cars fueling). This is where the time constant comes in. By measuring the time constant from the result of for different equations and comparing it to a maximum response rate they can monitor and determine a bad sensor with out the need for open loop o2 sensor checks. The sensor reports bad if the time constant is measured higher than the maximum set response rate.

I see no need to change this value unless you are using after market sensors connected to the ecu(not recommended) or what to know if your sensor is going bad sooner than factory tolerances you could possibly lower the value.

[4wheelinls1]

The transport delay is basically the length of time the air fuel mixture leaves the combustion chamber and reaches the sensor. This is effected by changing different headers that place the sensor closer or further from the combustion chamber.

There is also a response delay that oxygen sensors have due to the way they operate as a buffered system.

Regulations require that these sensors have a monitoring system in place. This is usually what causes the check engine light to come on in higher mileage Honda's and Toyota's. The codes are "catalytic inefficacy" and usually turn out to be a bad sensor. The way they are usually monitored requires the engine to go into open loop mode(ecu ignores sensors and runs off tables) as the sensors are being checked. This is why you can clear the code and it doesn't return for a few thousand miles until the next sensor check. This also can cause the engine to run a nonstoich afr for a short period, usually rich.

What Ford has done is take advantage of the inherent response delay in oxygen sensors in order to monitor them even while they are in closed loop mode(controling the cars fueling). This is where the time constant comes in. By measuring the time constant from the result of for different equations and comparing it to a maximum response rate they can monitor and determine a bad sensor with out the need for open loop o2 sensor checks. The sensor reports bad if the time constant is measured higher than the maximum set response rate.

I see no need to change this value unless you are using after market sensors connected to the ecu(not recommended) or what to know if your sensor is going bad sooner than factory tolerances you could possibly lower the value.

Cheers. I have been setting the transport delay like older Ford vehicle's. Happy to see thats ok. I'll keep leaving the time constant alone.