A datalog is a recording of what the engine did while you drove: airflow, fuel, timing, knock, temperatures, boost. It is the single most useful thing you can send a tuner, and with an RTD4 it takes a phone and a drive.
Before the first log
This is the setup from the instruction sheet that comes with every DEFI tune. You do it once.
- 01Create an HP Tuners TDN account, unless you already have one, and install the TDN app on your phone.
- 02Plug the RTD4 into the diagnostic port and pair it with the app. It may run a long update the first time — let it finish.
- 03Choose LINK YOUR TUNER and enter the invite code we send you. That connects your device to us.
Recording and sending a log
Logs are not sent to your tuner automatically. Uploading is the step people miss.
- 01With the engine warm, open the Data Log screen in the app and start logging.
- 02Drive the conditions we asked for. Stop the log when you are parked.
- 03Open View & Sync Files and upload the log. It reaches us through TDN.
- 04Tell us the fuel in the tank and anything that changed since the last log.
What makes a log useful
A log of the problem beats a description of it. If it stumbles at a certain speed, log that speed. If it pops on deceleration, log a few. If it is about power, the full-throttle part of the log is what matters — and that belongs on a track or a dyno, never on a public road.
- Warm the engine fully first; a cold log tells a different story
- One log per problem is better than one long log of everything
- Note the fuel, the outside temperature and any parts added
Check-engine light? Read the codes
The app reads diagnostic trouble codes from the car. Send them with a log and we can usually tell you whether it is the calibration, a sensor or something mechanical — and whether it is safe to keep driving.
Questions people ask
- Do I need a laptop to datalog?
- No. With an RTD4, logging and uploading are done in the TDN app on your phone.
- My log did not arrive. What happened?
- Logs are not uploaded automatically. Open View & Sync Files in the app and upload it; if a file has no green check, sync again.
- Can you read a log from a car you did not tune?
- Yes, as an expert log review. We read it and tell you in writing what it shows and what to do next.