TechWiki - User contributions [en-gb]

Passing your MoT Emissions Test

2006-08-30T09:28:52Z

217.160.76.165:

==Introduction==

Passing ones MoT emissions test with ones Elise appears to be an annual trauma. This page is the beginnings of a 'how-to' guide of hints and tips to help you through.

==A Brief Overview of Emissions Control==

Combustion engines of all types generally burn hydrocarbons (HC)as their primary fuel source.

In the limiting case, hydrocarbons combine with ambient oxygen (O2) to create carbon dioxide (CO2) and water (H2O), however an internal combustion engine is never 100% efficient and this chemical reaction usually has some incomplete products, namely carbon monoxide (CO) and unburned hydrocarbons (uHC).

In addition, the normally inert nitrogen (N2) in the air forms oxides of nitrogen (NOx) during the high temperature and pressure phases of the combustion process.

cont...

==The Lambda Sensor==

Otherwise known as an [[Lambda sensor|Oxygen Sensor]] or a HEGO sensor (Heated Exhaust Gas Oxygen), the [[Lambda sensor]] returns a voltage signal which is a non-linear function of the amount of oxygen present in the exhaust

[[Category:Exhaust]]

Passing your MoT Emissions Test

2006-08-30T09:28:19Z

217.160.76.165: /* The Lambda Sensor */

==Introduction==

Passing ones MoT emissions test with ones Elise appears to be an annual trauma. This page is the beginnings of a 'how-to' guide of hints and tips to help you through.

==A Brief Overview of Emissions Control==

Combustion engines of all types generally burn hydrocarbons (HC)as their primary fuel source.

In the limiting case, hydrocarbons combine with ambient oxygen (O2) to create carbon dioxide (CO2) and water (H2O), however an internal combustion engine is never 100% efficient and this chemical reaction usually has some incomplete products, namely carbon monoxide (CO) and unburned hydrocarbons (uHC).

In addition, the normally inert nitrogen (N2) in the air forms oxides of nitrogen (NOx) during the high temperature and pressure phases of the combustion process.

cont...

==The Lambda Sensor==

Otherwise known as an [[Lambda Sensor|Oxygen Sensor]] or a HEGO sensor (Heated Exhaust Gas Oxygen), the [[Lambda sensor]] returns a voltage signal which is a non-linear function of the amount of oxygen present in the exhaust

[[Category:Exhaust]]

Lambda sensor

2006-08-30T09:25:27Z

217.160.76.165: Minor edits to original

The '''Lambda Sensor''', also known as an Oxygen or O2 sensor, gives a voltage feedback to the ECU indicating the amount of oxygen in the exhaust stream, thus allowing accurate control over the combustion mixture. This is important to minimise emissions, maximise fuel economy and ensure the longevity of the catalytic converter.

On a standard Elise exhaust, it is located on the manifold downpipe, screwed into a threaded hole facing the front of the engine. It will (usually) have 4 silicone sheathed wires emerging from it, and may also have an outer heat resistant wrap covering the wires until they have run some distance from the exhaust.

The wires are usually colour coded as follows:

*White (x2) - heater wires. Voltage is supplied via these from the ECU to pre-heat the sensor to its operating temperature when the engine is warming up. Polarity is not important.
*Grey - sensor ground (earth)
*Black - sensor signal (+ve)

=====Correct Operation=====

A correctly operating sensor acts as a fuel cell, producing a voltage by electromechanical means, which typically ranges from around 0.2 volts in the case of a lean mixture to 0.8 volts for a rich mixture. The optimum mixture ratio is reached at around 0.45 volts.

=====Sensor Testing=====

*Disconnect the sensor from the ECU at the square, black plastic connector, so that the sensor's voltage may be measured in isolation.
*Attach an electronic voltmeter or oscilloscope (adjusted to a 1.0 volt range) across the black and grey wires attached to the lambda sensor. This can be done in a number of ways; paring back the insulation from the wires, attaching sprung probes directly to the pins in the connector, pushing pins or IDC splicing blocks through the insulation on the wires, etc. '''DO NOT''' use a moving coil meter to test the sensor, as its low internal resistance will almost certainly damage it.
*Start the engine and allow it to warm up for several minutes. As the heater wire has been disconnected from the ECU, it will take longer than normal for it to reach its 300 degree Centigrade minimum operating temperature.
*Examine the voltage output of the sensor. it should be greater than 0.2 volts. No voltage (or a very tiny voltage, far below 0.2 volts) most likely indicates a faulty sensor.
*Rev the engine and examine the change in voltage at the sensor. There should be practically no time delay between the engine being revved and a change in voltage at the sensor. A long delay may also indicate a faulty sensor.

=====Replacing the Sensor=====

This is commonly considered to be a complete pain, primarily due to the sensor's tendency to 'weld' itself into the screw fitting in the exhaust manifold, making it very difficult to remove. Access is also extremely tight, and it is likely that there will not be sufficient room to faclitate using a specialist oxygen sensor socket.

One suggested solution is to cut the wires to the sensor, allowing a suitably sized ring spanner to be used to attempt to remove it.

It is said that Lotus garages have their own special ways and means of removing these sensors, and this can involve removing the exhaust manifold entirely, especially where removing the sensor has led to the sensor mounting thread being stripped and having to be re-cut or helicoiled.

Lambda sensor

2006-08-30T09:18:02Z

217.160.76.165: Page created

The '''Lambda Sensor''' also known as an Oxygen or O2 sensor gives a voltage feedback to the ECU indicating the amount of oxygen in the exhaust stream, and to allowing accurate control over the combustion mixture. This is important to minimise emissions, maximise fuel economy and ensure the longevity of the catalytic converter.

On a standard Elise exhaust, it is located on the manifold downpipe, screwed into a threaded hole facing the front of the engine. It will (usually) have 4 silicone sheathed wires emerging from it, and may also have an outer heat resistant cover or wrap covering the wires until they have run some distance from the exhaust.

The wires are usually colour coded as follows:

*White (x2) - heater wires. Voltage is supplied via these from the ECU to pre-heat the sensor to its operating temperature when the engine is warming up. Polarity is not important.
*Grey - sensor ground (earth)
*Black - sensor signal (+ve)

=====Correct Operation=====

A correctly operating sensor acts as a fuel cell, producing a voltage by electromechanical means, which typically ranges from around 0.2 volts in the case of a lean mixture to 0.8 volts for a rich mixture. The optimum mixture ratio is reached at around 0.45 volts.

=====Sensor Testing=====

*Disconnect the sensor from the ECU at the square, black plastic connector.
*Attach an electronic voltmeter or oscilloscope (adjusted to a 1.0 volt range) across the Black and Grey wires attached to the lambda sensor. This can be done in a number of ways. Paring back the insulation from the wires, attaching probes directly to the pins in the connector, pushing pins or IDC splicing blocks through the insulation on the wires, etc. '''DO NOT''' use a moving coil meter to test the sensor, as its low internal resistance will almost certainly damage it.
*Start the engine and allow it to warm up for several minutes. As the heater wire has been disconnected from the sensor, it will take longer than normal for it to reach its 300 degree Centigrade minimum operating temperature.
*Examine the voltage output of the sensor. it should be greater than 0.2 volts. No voltage (or a very tiny voltage, far below 0.2 volts) most likely indicates a faulty sensor.
*Rev the engine and examine the change in voltage at the sensor. There should be practically no time delay between the engine being revved and the change in voltage at the sensor. A long delay may indicate a faulty sensor.

=====Replacing the Sensor=====

This is commonly considered to be a complete pain, primarily due to the sensor's tendency to 'weld' itself into the screw fitting in the exhaust manifold, making it very difficult to remove. Access is also extremely tight, and it is likely that there will not be sufficient room to faclitate using a specialist oxygen sensor socket.

One suggested alternative is to cut the wires to the sensor, allowing a suitably sized ring spanner to be used to attempt to remove it.

it is said that Lotus garages have their own special ways and means of removing sensors, and this can involve removing the exhaust manifold entirely, especially where removing the sensor leads to the sensor mounting thread being stripped and having to be re-cut.