Oxygen O2 Lambda Sensor 4 Wire Universal

Oxygen O2 Lambda Sensor 4 Wire Universal

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Oxygen O2 Lambda Sensor 4 Wire Universal

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The total for this item plus postage is:

UK: £16.49

OVERSEAS: £17.49

Cheques should be made out to "I. Simms"

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Kingfisher house, 25 Main Street, Gunthorpe, Notts, NG14 7EY

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Oxygen Sensors

Background

Oxygen sensors, colloquially known as “O2” or “Lambda” sensors, make modern electronic fuel injection and emission control possible. They determine if the air fuel ratio exiting a gas-combustion engine is rich (with unburnt fuel vapor) or lean (with excess oxygen). Closed-loop feedback-controlled fuel injection varies the fuel injector output according to real-time sensor data rather than operating with a predetermined (open-loop) fuel map. In addition to improving overall engine operation, they reduce the amounts of both unburnt fuel and oxides of nitrogen from entering the atmosphere. Unburnt fuel is pollution in the form of air-borne hydrocarbons, while oxides of nitrogen (NOx gases) are a result of excess air in the fuel mixture and cause smog and acid rain. Volvo was the first automobile manufacturer to employ this technology in the late 70s, along with the 3-way catalyst. Information on oxygen concentration is sent to the engine management computer or ECU, which adjusts the mixture to give the engine the best possible fuel economy and lowest possible exhaust emissions. Failure of these sensors, either through normal aging, the use of leaded fuels, or fuel contamination with silicones or silicates, for example, can lead to damage of an automobile's catalytic converter and expensive repairs. Tampering with or modifying the signal that the oxygen sensor sends to the engine computer can be detrimental to emissions control and can even damage the engine. When the engine is under low-load conditions (such as when accelerating very gently, or maintaining a constant speed), it is operating in 'closed-loop mode'. This refers to a feedback loop between the fuel injectors and the oxygen sensor, to maintain stoichiometric ratio. If modifications cause the mixture to run lean, there will be a slight increase in fuel economy, but a great increase in nitrogen oxide emissions, and the risk of damaging the engine due to detonation and excessively high exhaust gas temperatures. If modifications cause the mixture to run rich, then there will be a slight increase in power, again at the risk of overheating and igniting the catalytic converter, while decreasing fuel economy and increasing hydrocarbon emissions. When an internal combustion engine is under high load (such as when using wide-open throttle), the output of the oxygen sensor is ignored, and the engine automatically enriches the mixture to protect the engine. Any changes in the sensor output will be ignored in this state, as are changes from the air flow meter, which might otherwise lower engine performance due to the mixture being too rich or too lean, and increase the risk of engine damage due to detonation if the mixture is too lean.

Function of a Lambda (or Oxygen) Sensor

Lambda probes are used to reduce vehicle emissions by ensuring that engines burn their fuel efficiently and cleanly. Robert Bosch GmbH introduced the first automotive lambda probe in 1976, and it was first used by Volvo and Saab in that year. The sensors were introduced in the US from about 1980, and were required on all models of cars in many countries in Europe in 1993. By measuring the proportion of oxygen in the remaining exhaust gas, and by knowing the volume and temperature of the air entering the cylinders amongst other things, an ECU can use look-up tables to determine the amount of fuel required to burn at the stoichiometric ratio (14.7:1 air:fuel by mass for gasoline) to ensure complete combustion.

The Sensor

The sensor element is a ceramic cylinder plated inside and out with porous platinum electrodes; the whole assembly is protected by a metal gauze. It operates by measuring the difference in oxygen between the exhaust gas and the external air, and generates a voltage or changes its resistance depending on the difference between the two. The sensors only work effectively when heated to approximately 800°C, so most newer lambda probes have heating elements encased in the ceramic to bring the ceramic tip up to temperature quickly when the exhaust is cold. The probe typically has four wires attached to it: two for the lambda output, and two for the heater power, although some automakers use a common ground for the sensor element and heaters, resulting in three wires. Earlier non-electrically-heater sensors had one or two wires.

Zirconia sensors

The zirconium dioxide, or zirconia, lambda sensor is based on a solid-state electrochemical fuel cell called the Nernst cell. Its two electrodes provide an output voltage corresponding to the quantity of oxygen in the exhaust relative to that in the atmosphere. An output voltage of 0.2 V (200 mV) DC represents a lean mixture. That is one where the amount of oxygen entering the cylinder is sufficient to fully oxidize the carbon monoxide (CO), produced in burning the air and fuel, into carbon dioxide (CO2). A reading of 0.8 V (800 mV) DC represents a rich mixture, one which is high in unburned fuel and low in remaining oxygen. The ideal point is 0.45 V (450 mV) DC; this is where the quantities of air and fuel are in the optimum ratio, called the stoichiometric point, and the exhaust output mainly consists of fully oxidized CO2. The voltage produced by the sensor is so nonlinear with respect to oxygen concentration that it is impractical for the electronic control unit (ECU) to measure intermediate values - it merely registers "lean" or "rich", and periodically adjusts the fuel/air mixture to keep the output of the sensor alternating between these two states. The time period chosen by the ECU to monitor the sensor and adjust the fuel/air mixture creates an inevitable delay, which makes this system less responsive than one using a linear sensor (see below). The shorter the time period, the higher the so-called "cross count" [1] and the more responsive the system. The zirconia sensor is of the 'narrow band' type, referring to the narrow range of fuel/air ratios to which it responds.

Location of the Sensor in a system

The Sensor is typically screwed into a tapped hole in the exhaust, located after the branch manifold of the exhaust system combines, and before the catalytic converter. New vehicles are required to have a sensor before and after the exhaust catalyst to meet U.S. regulations requiring that all emissions components be monitored for failure. Pre and post-catalyst signals are monitored to determine catalyst efficiency. Additionally, some catalyst systems require brief cycles of lean (oxygen-containing) gas to load the catalyst and promote additional oxidation reduction of undesirable exhaust components.

Sensor failures

Normally, the lifetime of an unheated sensor is about 30,000 to 50,000 miles. Heated sensor lifetime is typically 100,000 miles. Failure of an unheated sensor is usually caused by the buildup of soot on the ceramic element, which lengthens its response time and may cause total loss of ability to sense oxygen. For heated sensors, normal deposits are burned off during operation and failure occurs due to catalyst depletion, similar to the reason a battery stops producing current. The probe then tends to report lean mixture, the ECU enriches the mixture, the exhaust gets rich with carbon monoxide and hydrocarbons, and the mileage worsens. Leaded gasoline contaminates the oxygen sensors and catalytic converters. Most oxygen sensors are rated for some service life in the presence of leaded gasoline but sensor life will be shortened to as little as 15,000 miles depending on the lead concentration. Lead-damaged sensors typically have their tips discolored light rusty. Another common cause of premature failure of lambda probes is contamination of fuel with silicones (used in some sealings and greases) or silicates (used as corrosion inhibitors in some antifreezes). In this case, the deposits on the sensor are colored between shiny white and grainy light gray. Leaks of oil into the engine may cover the probe tip with an oily black deposit, with associated loss of response. An overly rich mixture causes buildup of black powdery deposit on the probe. This may be caused by failure of the probe itself, or by a problem elsewhere in the fuel rationing system. Applying an external voltage to the zirconia sensors, e.g. by checking them with some types of ohmmeter, may damage them.

Please contact us for overseas postage rates on this item

This is a top quality 4 wire universal sensor for petrol engines.

Will it fit my car ?

The best way to determine if it will fit your car is to count the number and colours of the wires on your existing sensor. If your existing sensor has the same number and colour of wires 1 Black in this case, then you can be 95% certain that this sensor will do the job. For the more technically minded this is a Zircona type sensor (see more info for explaination).

The thread size is 18mm and the spanner size is 22mm. This sensor will not replace "Titania" or "Planar" type Sensors.

The main dealer price is £70 for this, why such a low price ?

This sensor is not fitted with the (expensive) connector that the main dealer part comes with. Just cut the plug off the existing sensor and use the crimps provided to re use the original connector to connect this sensor to the car.

This sensor has been manufactured to the highest standards in a multi million dollar factory with ISO9000 and ISO14000 quality certification. It is NOT, repeat NOT made in China.

How do I fit it ?

It is not much more difficult than fitting a spark plug! Remove the existing sensor. Clip the connector off. Measure the wire length required (our sensors come with long wires to allow cutting down) and use the crimps provided to connect the new sensor. Fit the new sensor into place and tighten and re connect the wiring. (There are full instructions in the packet).

Common mistakes

The sensor works at less than half a volt so the connections have to be securely made.

Using Copper grease when fitting will poison the chemical reaction that makes the sensor work (our sensors are supplied with a special anti sieze compound pre applied and are ready to fit)

Measure twice, cut once when clipping the wires back

Typical Sensor Failure Symptoms

The "Engine Management" light comes on (usually an orange light with an engine symbol on it)

Poor fuel economy and / or black smoke

An MOT Failure ticket !


More information on O2 Lambda Sensors

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