Datalogging Basics

Introduction

Tuning your car, ultimately, is a scientific endeavor. Without accurate data, you have little if anything to inform your decisions (inputs) to your tune as you reform it to meet your goals. Data-logging is an important method to receive feedback from the ECM (engine control module) for your engine's current condition and performance as it relates to your calibration (tune) on the vehicle.

Typically, a datalog is the recording of a series of values (or parameters) that are read (or polled) from the vehicle at a specific interval, or polling rate. Parameters included in a data log might be, for example, the engine speed (RPM), rate of mass air entering the intake tract (mass airflow, or MAF), ignition advance (or ignition timing), the air-fuel target ratio (or commanded AFR), coolant temperature, camshaft phase/timing, and so on. Each of these parameters are requested at once by your tuning software, such as Atlas, at a certain frequency schedule typically measured in polls-per-second or hertz (Hz).

The ECM records these values to Atlas by first briefly pausing the execution of the ECM logic, reading every value requested, and assembling all requested parameters in a single frame that is transmitted back to Atlas over the vehicle's communication system (typically the CAN bus). Atlas then records the date and time that the individual frame was received and adds it to the list of frames, which together form the recording.

The same system that is used to display gauges in Atlas is used for data-logging. The difference is these received (polled) frames are recorded for later viewing, as opposed to gauges which only use any given frame to update the gauge's corresponding parameter value and throw away the received data after it has been displayed on screen.

Atlas Datalogger