Specifications

Engine Management and Data Acquisition SystemsPage 72
4 Wire Wide Band Lambda Sensor
is technology takes advantage of the fact that a 4 Wire Wide Band Lambda sensor’s voltage output is based on not only the oxygen differential
between the exhaust pipe and atmosphere, but also is dependant on the temperature of the sensor itself. Sensor impedance varies with temperature, so
a MoTeC ECU measures not only Wide Band Lambda Voltage, but also the sensor impedance. It is not possible to properly display lambdas without
monitoring the sensor temperature. Systems which do not use at least a 4 wire sensor typically have errors in displayed lambda as high as 8%!
5 Wire Wide Band Lambda Sensor
is newer technology is used to determine the air fuel ratio of an engine by measuring lambda sensor output and measuring the current required to
hold the sensor voltage output constant. An oxygen sensor produces voltage and a small amount of current as oxygen atoms pass across its substrate
from high concentration to low concentration. e greater the flow of oxygen, the greater the voltage produced. is is the case when a rich mixture is
encountered. Conversely, when current is applied to an oxygen sensor, oxygen atoms are moved from a low concentration to a high concentration or
vice versa depending on the polarity of the current applied. e MoTeC M400/600/800/880 ECU’s are capable of measuring this type of sensor input
which offers increased speed and accuracy over the older technology 4 wire sensors. M4 and M48 ECU’s can leverage the 5 wire technology by connect-
ing a MoTeC PLM, which has a definable analog voltage output, to the Lambda input on the ECU.
Bosch LSU and NTK UEGO Sensors
Both the MoTeC M400/600/800/880 and the MoTeC PLM are capable of operating with either the NTK UEGO or the Bosch LSU-4 5 wire wide
band sensors. Of the two, the NTK is most accurate. It is a true laboratory grade sensor. Its accuracy has been found to be about 1.5% better than that
of the Bosch LSU. Additionally the NTK has a better response time than does the LSU again about 1.5%. e NTK is the benchmark against which
the LSU is measured. e advantage of the LSU sensor is its lower price compared to the NTK. If you are doing very precise and accurate laboratory
type testing, the NTK is the sensor for you. Both sensors have a life expectancy of 500 hours on unleaded fuels and that number is diminished to 50
hours using leaded fuels. Lambda Sensors are very similar to spark plugs with respect to their estimated life expectancy. Spark Plugs are designed to last
40,000 miles under optimum circumstances but they can be damaged in less than 1 mile by misuse. A lambda sensor can be thought of the same way.
Misuse by overly rich mixtures, high temperatures, overtightening or dropping can have a very negative effect on lambda sensor life. Like spark plugs,
lambda sensors cannot be returned under warranty.
What is Lambda?
Lambda describes an equivalence value in percentage of the chemically correct air-to-fuel ratio for any type of fuel. If the air fuel ratio measured in the
exhaust pipe of an engine is at the chemically correct (stoichiometric) ratio of air-to-fuel, lambda is equal to 1.0. In the case of gasoline, lambda 1.0 is
equivalent to 14.7:1 air-to-fuel. Lambdas less than 1.0 indicate the engine is running richer than stoichiometric, while lambdas greater than 1.0 indi-
cate a lean mixture. If we measure a lambda value of 1.06 and we want a lambda value of .95, we simply increase the fuel delivered to the engine (pulse-
width) by 11 percent. is will place us exactly at .95 lambda. By using the Lambda Was or the Quick Lambda functions a tuner can quickly shape the
fuel table to match the engine’s exact requirements. In addition, the W Lambda function copies the Quick Lambda value to the sites immediately to the
right and up above to help keep the fuel table variance from one site to another at a minimum.
Quick Lambda and Lambda Was
A MoTeC ECU, allows the user to define a lambda goal table based on load and rpm. e Quick Lambda function in the software allows a tuner to
quickly adjust the values in the fuel control table to achieve the goal lambda, based on the lambda reported by the sensor. If the reported lambda is
.98 and the goal is .93, the ECU automatically jumps to the current load site, and multiplies the value in the site by 1.05. e next time the engine
runs in that site, the lambda will be .93. Similarly, Lambda Was allows a user to locate a load and rpm site in the main fuel table and enter a recorded
lambda measurement from a data log. e ECU multiplies the load site value by the difference between entered lambda and the goal lambda value
so that the engine will achieve the goal lambda the next time it runs on that load site. is makes tuning much faster and easier than calculating the
required enrichment based on an air fuel ratio number. Of course you can manually do multiplication, division, addition and or subtraction on any site
or a number of sites with only a few keystrokes, and the overall trim function allows you to trim the entire fuel or ignition table up or down based on
percentage.