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House guide · 02
Capturing a useful datalog
A good log gets you a good answer. Here’s what to log and how to drive it so we can see what the engine is actually doing.
Channels to log
| Channel | Why |
|---|---|
| RPM, MAP / boost, TPS | Where the engine is in the map |
| Wideband AFR / lambda | Required — fueling accuracy |
| Target AFR / lambda | How far off target you are |
| Ignition timing | Timing in each cell |
| Injector duty / pulse width | Fuel system headroom |
| IAT and coolant temp | Temperature corrections |
| Fuel pressure | Supply health under load |
| Knock level (if equipped) | Safety margin |
| Ethanol content (flex) | Blend corrections |
| Battery voltage | Injector and coil behavior |
Log rate
Use at least 20–50 Hz for drivability logs and the highest rate your ECU allows for full-load pulls. Start logging before the car starts and stop after it shuts off.
The drive
- Cold start and two minutes of idle
- Light cruise at steady throttle in a few gears
- Gentle tip-in and tip-out
- Load and boost only on a dyno, track, or closed course
- Note anything odd and the time it happened
Before you send it
- Send the log file and the exact map that was running
- Tell us the fuel in the tank and the outside temperature
- Name files with the date, e.g. 2026-11-09_idle_cruise
Ignition House · [email protected] · General guidance only. Follow your ECU manufacturer’s documentation, and get qualified help for anything you’re unsure about.