Technical Information

Bosch Calibration Chip

The WMS Wideband O2 Sensor uses the Bosch calibration chip, the correct way to calibrate the sensor as engineered by Bosch. Here is how it works. Each Bosch LSU4 sensor contains a laser trimmed calibration resistor, the Bosch calibration chip on board in the WMS Wideband reads the sensor calibration and loads it so each sensor is calibrated exactly. The Bosch calibration chip also controls the heater, and this calibration is done only when the sensor is at operating temperature.

Heater Circuit

Control of the heater circuit is one of the most critical aspects of the wideband sensor and any variations in the heater will cause inaccurate readings of AFR. The sensor must be kept at a nominal operating temperature of 750?C. The WMS Wideband uses the Bosch calibration chip and a pulsewidth controlled PID feedback loop to control the temperature of the sensor with no oscillations.

Sample Rates

The sensor is sampled at 100x per second and our controller uses 16x oversampling to calculate the AFR. The display is updated 8x per second, a rate compatible with the human eye. There is no delay from calculation to display of AFR.

O2 Sensors

Most cars produced after the 1980s, and all since 1996, have at least one oxygen sensor. It is a part of the emissions control system and is also a part of the engine management system. Oxygen sensors help the engine run efficiently.

Different fuels have different stoichiometric values, e.g. methanol 6.4:1 and ethanol 9.0:1. Theoretically gasoline burns completely at an air to gasoline ratio of 14.7:1. This value is gasoline's "stoichiometric" value.

When the air-fuel-ratio (AFR) in the combustion chamber of your engine has less air than the stoichiometric value, then the AFR is said to be "rich," rich in fuel. If there is more air than stoichiometric, then the AFR is "lean," lean on fuel. The AFR variance indicates the deviation of the actual AFR from the theoretically required ratio for complete combustion. The value of this variance is represented by the Greek symbol called "lambda," and is calculated by dividing actual induced air mass by the theoretical air requirement.

Variations from the stoichiometric air-fuel ratio result in pollutants. Excess, unspent fuel in the combustion process results in hydrocarbons (HC) and carbon monoxide (CO). Excess air causes increased nitrogen oxides (NOx). Catalytic converters help reduce the HC, CO, and NOx emissions if the engine is operating around the stoichiometric AFR.

Oxygen sensors measure AFR post-combustion. They are positioned some distance down the the exhaust pipe in order to ensure that the sample they measure is representative of the AFR in the cylinders. Oxygen sensors can identify variations from the ideal AFR and tell the engine management system to adjust the ignition and injection processes accordingly. So what is the difference between narrowband and wideband O2 sensors?

Wideband O2 Sensors -- What is the difference from narrowband O2 sensors?

Narrowband O2 sensors are designed only to measure the stoichiometric air-fuel-ratio (AFR) for gasoline, i.e. 14.7:1. Wideband O2 sensors have a broader effective range of sensing. The effective ranges of narrowband (upper image) and wideband O2 sensors (lower image) are represented in the two graphs to the right . The voltage range between the two black bars indicates the greater range of the AFR in which a wideband O2 sensor can operate. Narrowband sensors can only tell you when the AFR is 14.7:1. Although it can also tell you when you are richer or leaner, it cannot tell you by how much. A wideband O2 sensor can.

Designed to measure a broader range of AFR  (9.65:1 to 20:1), Wideband O2 sensors are more effective instruments for tuning your engine. They can detect variations of the AFR better than stock narrowband O2 sensors. The result is that you can tune your engine and modify your management system according to your use and performance level. But who needs to measure a wide band of AFRs?

AFR Tuning with Wideband O2 Sensors -- Who needs it?

Dyno-tuning shops and racers know that the WMS Wideband O2 System helps them to analyze engine performance in the shop and to monitor car performance while on the track. They can also log air-fuel-ratio information throughout the course of a race in order to analyze that information later.

For those with turbo or a supercharger the WMS Wideband O2 System is a must, because a lean AFR can cause engine damage. These applications need to run quite rich, i.e. between 11.5:1 - 13.0:1 to be safe. Only the wideband O2 sensor will measure in this range.

When changes in the AFR could be caused by changes in tune or problems like a weak fuel pump, loss of fuel pressure, dirty fuel filter, or even changes in atmospheric conditions, the WMS Wideband O2 System helps monitor your engine's performance and trouble-shoot engine performance before serious problems occur.

However, AFR tuning is not just for engines with serious power-adders and those who who are hardcore racers. The WMS Wideband O2 System is designed for anyone who wants to get the full performance from their vehicle.

Bolt-on performance parts increase the horsepower and torque of your naturally aspirated engine, but until you tune your engine, you will not make full use of those parts. This is where the WMS Wideband O2 System comes in. A naturally aspirated performance engine typically has a AFR of 13.0:1, but lose power when run richer, i.e. around 12.5 - 12.0:1.

Although an absolute must for supercharged or turbo applications, all performance engines can benefit from the addition of the WMS Wideband O2 System. Anyone who tune their engine, including carb jetting or changing carbs, chips or software for stock engine management computers, piggy back systems, stand alone DFI systems. Even if your tuning by changing fuel pressure using the WMS Wideband O2 System will help.

Bosch LSU 4.2 O2 Sensor

Installation of the Bosch LSU 4.2 O2 Sensor (click image to enlarge and see above right for larger diagram of sensor) in the exhaust system must be at a point guaranteeing representative exhaust gas composition whilst also satisfying the specified temperature limits (see above right).

"The heater power must always be switched on power controlled (e.g. duty cycled heater power). This is necessary to reduce thermal stress of the sensor element at cold start due to high peak power in the first seconds.

The active sensor ceramic element is heated up quickly when the heater power is switched on. This means that the sensor installation location must be selected to minimize exhaust side stressing of the sensor ceramic element with condensation water in order to prevent ceramic element cracking.

Locate sensor as close to the engine as possible, respecting maximum allowed temperature range (see the top right column of this page). Attempt to achieve rapid heating-up of the exhaust pipes in the area in front of the sensor.

The exhaust pipe in front of the sensor should not contain any pockets, projections, protrusions, edges, flex-tubes etc. to avoid accumulation of condensation water. A downwards slope of the pipe is recommended. Make sure, that the front hole of the double protection tube does not point against exhaust gas stream.

It must be assured, that when the sensor is operated, the connection to the control unit is save and not disconnected during operation, or that the control unit diagnosis recognizes a failing connection. It is also not allowed, to disconnect or to connect the sensor to the control unit or ECU while the sensor or control unit is being operated.

The control unit may only be switched on after the sensor is connected completely. The sensor cables may never be connected in the wrong way or wrong polarity, otherwise the sensor might be destroyed."

Source: Bosch  Y 258 K01 005-000e

Bosch LSU 4.2
Wideband O2 Sensor

Technical Information on the Temperature Maximums for the Bosch LSU 4.2 O2 Sensor

Maximum temperatures (max. 250 h accumulated over lifetime) at sensor element = 1030 degrees C. At the mounting point ("hexagon") of the sensor housing (see expanded image above for diagram specifics) = 630 degrees C.

"If the exhaust gas temperature of 850 degrees C is exceeded, the heater power must be switched off. In this case the accuracy of the sensor signal is limited. If the maximum gas temperature exceeds 850 degrees C or hexagon temperature exceeds 500 degrees C, the use of a longer thread boss is recommended.

If the operating temperature is exceeded (within the max. temperature limits) for more then 10 minutes without break, the sensor function might be affected during this time."

Source: Bosch  Y 258 K01 005-000e