ThunderMax EFI and wideband AutoTune
How a replacement ECM uses wideband feedback, and how to find the right kit for your Harley.
What ThunderMax replaces
A ThunderMax EFI kit replaces the factory engine control module on a supported Harley-Davidson. The kit pairs the replacement ECM with wideband oxygen sensors. A base map provides the starting calibration, and ThunderMax uses sensor feedback to correct fueling while the bike runs.
ThunderMax documents software for viewing operating data and editing calibration settings. Check the kit’s documentation for available controls and logging on the motorcycle you’re working on.
Match the engine family, not just the year
ThunderMax lists the 309-605 for supported 2023.5 and newer center-cooled Milwaukee-Eight Touring models, including VVT and non-VVT applications. The 309-591 listing covers a separate Touring application without the center-cooled engine. A Touring model year alone is not enough to choose between them.
- Confirm the exact model, engine, and ECM kit in ThunderMax’s current application listing.
- Check the oxygen sensor mounting provisions and the kit’s included sensors and harnesses.
- Confirm the base map and any functions you rely on, such as ride modes, knock control, or diagnostics, for that exact application.
Compare results against your starting map
When sharing results, identify the ECM part number, software and base map versions, and what hardware is on the bike. Keep your first log so you can compare subsequent fuel corrections under similar conditions.