EGT sensors – everything you need to know (and then some)
What is an EGT?
EGT stands for Exhaust Gas Temperature, and to measure it we use EGT sensors. The most common EGT sensor is a K-type thermocouple, but not all K-type thermocouples are used to measure the exhaust gas temperatures.
You see we could also use K-type thermocouples to measure air temperatures, coolant temperatures, oil temperatures or anything else you can gain access to and install a K-type thermocouple on.
What is a Thermocouple
A thermocouple is a temperature sensor made up of two dissimilar metals. At different temperatures, the dissimilar metals react to each other differently and produce a tiny amount of voltage.
We can put that voltage through an amplifier and, as long as we know the metals we are working with, we can come up with a temperature calibration chart, thus calculating what temperature the sensor is measuring.
There are several different EGT material types that are known by their lettering: J, K, T, N, E, B, R, S and more. Each letter assignment has different working temperature ranges, is made of different materials, has different acceptable error ranges and different life expectancies.
The most common Thermocouple type in our Automotive world is the K Type. The K Type Thermocouple is made up of Nickel-Chromium and Nickel-Alumel, which gives this sensor an operating range of -200 Celsius to 1260 Celsius. They are inexpensive, reliable, highly accurate and have that wide temperature range.
The Haltech brand K-type sensors come terminated into the 2 pin connector known as a Mini-K type connector. You can specify the cable lengths you need which makes fitting sensors easy – simply plug them straight into the required thermocouple amplifier.
If you are terminating your own K-type thermocouple sensors into the amplifier make sure to get the wiring around the right way – it's important.
The yellow wire is the Positive signal and is the pin made of Chromium. The Red wire is the Negative signal and is the pin made of Alumel. If you open the Mini K-type connector there will be a + and – symbol there to help identify which pin is which
Shapes and sizes
The sensors come in a range of different physical appearances and shapes.
The sensors used to measure exhaust gas temperatures are typically 1/4inch open tip, but you can also get 1/8 inch open or closed tip sensors. The sensor you choose would depend on your application, but typically the ¼ inch open tip is the most common for EGTs.
The difference between an Open or Closed tip is in the response time and reliability. An Open tip sensor will react to a temperature change in around 200ms, while a closed tip sensor will react in around 800ms – a bit slow if you are looking for rapid changes like an ignition misfire.
You can also get K-type thermocouple that look like a washer, these are perfect for fitting under a bolt head to measure surface temperatures. A 1/8 closed tip sensor would be perfect for measuring fluid temperatures because you wouldn’t want to submerge an open tip sensor for too long.
Where and how deep?
It’s important that all your EGT sensors are installed at the same distance from the cylinder head and at equal depths.
The depth will depend on the type of induction you’re running – in naturally aspirated engines the probe needs to sit in the centre of the pipe while in engines with forced induction the probe will be no more than 6mm into the pipe, so much shallower than in N/A engines.
Amp it up!
The K-type thermocouple requires an external amplifier to get the data into the ECU. This is due to the fact that the thermocouple itself only outputs a voltage of around 60mv across its almost 1500c working range.
The amplifier is there to convert this tiny voltage into data we can use in the ECU. The Thermocouple Amplifier (TCA) integrates with the engine management system via the CAN communication system.
It’s amazing to think these sensors have a working range of 1500 degrees Celsius, given they are basically just made up of two dissimilar metals bonded together to make a tiny voltage, which is then amplified for the ECU to see and they do it while maintaining a maximum error of just 2.2 degrees Celsius which is less than 1%!
Setting it up
Once you have the thermocouple probes installed and connected to your TCA (Thermocouple Amplifier) it’s just a simple matter of connecting the TCA to your Haltech ECU and setting the EGTs up in the Haltech software.
You will find the EGTs under “Sensors”. In the “Display” menu you will need to set up your minimum and maximum display temperatures as well as minimum and maximum warning temps. These temperatures determine a range at which your ECU will log the EGTs.
The “Diagnostic” menu lets you keep an eye on each individual EGT sensor and identify any potential problems like voltage/temperature spikes or drops which will then can trigger an error code.
All your connections are set up in the “Wiring” menu. This is where you connect your EGT sensor to an available channel and define the sensor type.
In this case we’re using a Haltech K-type thermocouple which is chosen through a drop-down menu. If you’re using Haltech’s K-type sensors, you don’t need to calibrate them, all the information is already set for you in the software.
We can also use EGTs to trigger an individual cylinder shut down. Scroll down to “Engine Protection” and set your shut-down parameters for each cylinder in the “Cylinder Shutdown” menu.
And that’s about it. Remember, if you have any questions or need a hand setting up your Haltech ECU we are always happy to help – contact us on support@haltech.com.
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