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ECMLink 101 - Datalogging basics

On this page, we're going to assume you've already run through the install procedure and have gotten a good connection established with the ECU. If you have not, please review the Installation page first.

We are also going to assume you have already walked through the basic Initial checks page. If not, please do so!


This section is out of sequence, but it's so important that I want to mention it first. If you want to display items in your log file that are not currently available, you must add the items to the ECU first! You do this using the Edit→Captured values (F10) dialog. Once you have told the ECU you want it to log a new value, you can then display that value on the screen using the Edit→Display values (F9) dialog.

Starting a datalog

There are two “modes” of logging in ECMLink.

Streaming to screen

“Streaming” (F11 or ECU→Start stream) receives data from the ECU and displays it on the screen but does not save the data to disk. This can be useful for quick checks or diagnostics.

Capturing to disk (and screen)

“Capturing” (F12 or ECU→Start capture) does the same as streaming, but also writes the data to a log file automatically. The name of the log file it creates is determined by the Filenames preferences (Edit→App preferences). Pull up this dialog and hit the “?” at the bottom for a lot more information on how filename preferences can be configured.

What's in a datalog

When you capture a datalog, the file will contain the data logged from the ECU as well as all the settings and direct access configuration data that were in place at the time the datalog was started.

When you open a previously saved datalog, you can review the settings and direct access data saved with that datalog by right clicking in the graph area and selecting “ECU config (from log)” (F7) or “ECU direct access (from log)” (F8). Either will open a new tab with data displayed from that log file.

NOTE: With a V3 ECU, it's possible to change ECU settings while a datalog is being captured. Please be aware that doing this can cause a lot of confusion when reviewing the log file because it will not be clear which settings are in place at any given moment in the log.

How logging works

Telling the ECU what to log

To optimize logging speed, ECMLink uses a “streaming” mode of communication with the ECU while logging. Basically, the application tells the ECU to start sending data and the ECU responds by sending out a constant, repeating sequence of data elements captured from memory. In order for this to work properly, the application and ECU must agree on which data elements are going to be sent and in which order.

You tell the ECU what to send by using the Edit→Captured values (F10) dialog. When ECMLink connects to the ECU, it asks the ECU for a list of what it is currently configured to log. You then use the captured values dialog to change that list.

Showing items on the screen

You may not always want to display every value captured from the ECU. You might capture 20 different items, but only be interested in seeing 10 particular items on your graph at one time (possibly to reduce screen space or reduce clutter in the graph, for example). You can configure what will be displayed on the graph using the Edit→Display values (F9) dialog. This menu item only works while viewing a datalog tab.

The display values dialog will present you with a list of what can be displayed given the current set of things captured from the ECU. If you want to display a value that's not listed in the display values dialog, then you'll need to first tell the ECU to log that value. You do that using the Edit→Captured values (F10) dialog as described above.

ecmlink101datalogging.txt · Last modified: 2009/05/28 07:47 by twdorris