Why onboard logging matters
Most problems don't happen while the laptop is connected. A misfire at the top of fourth gear, a fuel pressure dip on a long corner or an intermittent sensor fault all show up in the real world. Onboard logging captures those moments in the ECU's own memory so you can pull the log afterwards and see exactly what happened.
Choosing when logging runs
The Datalog settings decide when the logger is recording. You can use more than one trigger, and they're treated as OR conditions: as soon as any one of them is true, logging starts.
| Option | What it does | When we use it |
|---|---|---|
| Always On | Records whenever the ECU has power | Race cars and development work, where you want everything |
| Datalog Switch Input | Records while a switch input is on | When the driver wants to capture specific runs. Set the input up in Datalog Switch |
| Channel condition (Enabled) | Records while a chosen channel meets a rule you set | Street cars, so memory isn't filled with idling |
| Logger Off Delay | Keeps recording for this long after the trigger drops out | So you catch what happens right after the event |
Setting up a channel condition
- Tick Enabled, then click Select and pick the channel to watch.
- Choose a comparison from the drop-down, for example Greater Than.
- Type the value in the last field.
A condition we use a lot is engine speed greater than zero, so the log runs whenever the engine is running. Another is manifold pressure above atmospheric, which records only when the car is on boost.
Choosing channels
A Nexus R5 can record up to 300 channels at once internally, at rates up to 1 kHz. Click Add/Remove Channels, highlight what you want in the list, and use the >> button to move them into the selected side. Click OK when you're done.
Our core list for a tuned street car: RPM, manifold pressure, throttle, lambda and target, fuel trims, ignition timing, knock, coolant and air temperature, fuel and oil pressure, battery voltage and injector duty. Add anything specific to the car, such as boost target, gear or wheel speeds.
Sample rate
Sample rate is how often a channel is recorded, shown as a frequency and the matching time gap. At 10 Hz, one sample is taken every 100 ms. At 200 Hz, one every 5 ms. Pick the rate from the Sample Rate drop-down.
Match the rate to how fast the signal changes. Temperatures barely move in a second, so a slow rate is plenty. RPM, throttle, knock and pressure signals change fast and benefit from a higher rate. Recording everything at the maximum rate fills memory quickly without adding useful detail.
Set logging up before the car leaves the shop, even on a street build. When a customer calls with a problem, a log turns a guessing game into a quick diagnosis.
On an Elite ECU the equivalent setup is in Datalog for Elite. You'll find Nexus ECUs in our NEXUS R5 lineup.
