A data log is commonly used when you need to pinpoint data from your car's electronic control unit (ECU). A data log is typically required for tuned and modified cars to ensure their engine runs the way it should. As most of us have probably encountered, automobiles can be very temperamental, and locating your issue is difficult, especially without professional help.

So, here's what data-logging is and why it's useful for all car owners.

How to Data Log Your Vehicle

image of datalogging in a vehicle

Data-logging is a feature that comes with most ECU tuning suites. Gathering a data log is as simple as connecting your car with your supplied OBD-II cable and pressing Start. Each ECU tuning suite is slightly different, but the process should remain relatively unanimous.

When data-logging, it is best to recreate any driving conditions your car may face—varying speeds and RPM range. In addition, it is wise to record concise data logs, as it is harder to locate problems in larger files.

How to Import Your ECU Data Log and Use the Information

After completing your data log, you will be prompted to save the file. It is imperative that you name the data logs accordingly to your driving characteristics, which will help you easily identify specific files when you import the data into a spreadsheet.

Although there are a few methods of viewing a datalog, one method is to import the data using spreadsheet software such as Excel or Google Sheets. This is done by importing one of your datalog files (using a CSV file) into said spreadsheet software. You may be prompted to convert the data to make it viewable in the program.

importing csv file into google spreadsheet

For those that prefer physical graphs, most tuning suites come with the ability to display datalog. After successfully importing your CSV file, you will see rows of data ranging from your engine's RPM to load percentages, all data collected from your engine control unit (ECU).

How to Read the Data Log

datalog picture

Using the information from the imported CSV file, you should be able to see different categories on both the X and Y axes. As shown in the image, a plethora of information is displayed on the spreadsheet.

You can use this to pinpoint any problematic issues with your vehicle. Furthermore, you can locate any discrepancies between requested and actual data, making pinpointing issues exponentially easier.

Each column on the X-axis is representative of a different parameter measured. Among the parameters listed, here are your primaries:

Engine Speed

The engine speed is an alternate name for RPM (revolutions per minute). This is the speed at which the internal components of your engine are spinning.

TPS (Throttle Position Sensor)

The TPS column on the spreadsheet retrieves data from your car's throttle position sensor. This value will make it easier to identify if you are driving under a heavy load or coasting.

Knock

Engine knock is when your engine cannot burn the fuel mixture inside your cylinders. This is commonly due to the mixture of fuel being of poor quality.

Lambda

Your lambda value is derived from the stoichiometric air/fuel ratio and obtained with your oxygen sensors. This perfect ratio is needed for combustion cycles, around 14.7:1.

The Importance of Data Logging For Tuned Cars

Completing a data log from time to time is important for those that own modified or tuned vehicles. As intelligent as your ECU is, not all issues present themselves and immediately trigger the vehicle's check engine light.

Reading a datalog isn't too challenging when you have the right tools. With second to second live data and rows of information, pinpointing any issue in your vehicle by using a datalog will be clear as day.