Get this page right before you crank
Everything else in ignition tuning assumes the ECU knows how your coils are laid out, how they are triggered and how they charge. Unlike most tuning tables, there's no "close enough" here. Edge and dwell mode especially are set by the igniter design. Check the coil or module maker's data, then set the page before the engine turns over. Our engine configuration guide covers the settings that come first, like cylinder count and firing order.
Ignition Mode
| Mode | Hardware | How outputs are used |
|---|---|---|
| Direct Fire | One coil per cylinder | One output per cylinder, numbered by cylinder (Ignition 1 to cylinder 1 and so on). The firing order on the engine configuration page sets the sequence |
| Wasted Spark | Each coil fires two cylinders, or each output drives a pair of coils | Half as many outputs as cylinders, fired in plain sequence. The firing order setting is ignored |
| Distributor | One coil feeding a distributor | Ignition 1 only |
| Twin Distributor | Two coils and two distributors, like a Toyota 1UZ-FE with one per bank | Ignition 1 for bank 1, Ignition 2 for bank 2 |
| Single Wire CDI | Haltech Power Select 4, 6 or 8 CDI only | Ignition 1 carries the multiplexed trigger. Ignition 2 handles automatic power selection on 4-stroke engines, Ignition 3 on rotaries |
A common direct-fire mistake is wiring outputs in firing order rather than cylinder number. On a Nexus, output 1 goes to cylinder 1, output 2 to cylinder 2, and the ECU handles the order.
Edge: which transition fires the spark
Every ignition output spends part of each cycle charging the coil and then switches to fire it. The Edge setting says which direction of switching triggers the spark. The default is Falling.
- Falling: the output rests at 0 V, rises to the pull-up voltage to start charging, and fires as it drops back to 0 V. Almost all factory ignition systems and most aftermarket coils and igniters use this.
- Rising: the output rests high, drops to 0 V to start charging, and fires as it rises back up. It is used by some CDI boxes designed to replace points and by some factory Honda distributors.
With the wrong edge, the ECU charges the coil for most of the cycle instead of a few milliseconds. Coils and igniters get hot very quickly. If a coil is warm after a brief key-on with no cranking, stop and check this setting.
Dwell Mode: who controls charge time
Like edge, there is only one correct choice for a given igniter. The default is Constant Charge.
- Constant Charge: the ECU controls the charge time directly. This is the norm for factory systems where the ECU controls timing, whether the igniter is a separate module or built into the coil. Choosing it unlocks a 3D dwell table in milliseconds. Take the values from the coil maker, not from a guess.
- Constant Duty: the module handles charge time itself, and the ECU just sends a fixed-duty square wave. Some points-replacement CDI units and older modules like Ford's TFI work this way. It unlocks the Dwell Duty setting, which is usually 50% for these systems. Confirm with the ignition maker before running it.
Rotary engines: Trailing Edge and Trailing Dwell Mode
These only appear when the Engine Type is Rotary. They work exactly like Edge and Dwell Mode but apply only to the trailing coils. The leading coils follow the main settings, so a rotary can run different igniters on leading and trailing plugs.
Pull Up Voltage and Time Offset
| Setting | What it does | Our advice |
|---|---|---|
| Pull Up Voltage | Voltage the ignition outputs are pulled up to. It applies to every ignition output, even ones assigned to other functions | Leave at the default, Battery Voltage, unless your igniter maker says otherwise |
| Time Offset | Fires the outputs early by a set number of microseconds to make up for delay between the trigger and the actual spark | Default 0 µs. Only change it if timing light checks show timing retarding as RPM rises and the delay is in the ignition hardware |
Troubleshooting
| Symptom | Usually |
|---|---|
| Coils hot, no spark | Wrong Edge setting |
| Weak spark or high-RPM misfire | Dwell too short, or Constant Duty selected for a coil the ECU should control |
| Runs, but only on some cylinders | Direct fire outputs wired in firing order instead of cylinder order |
| Timing right at idle, retards at high RPM | Trigger or ignition hardware delay. See calibrating ignition timing |
FAQ
Should I run wasted spark or direct fire?
If you have one coil per cylinder and enough outputs plus a cam signal, direct fire. Wasted spark is fine when outputs are short or when the trigger has no cam reference.
How do I know my coil's edge and dwell?
Check the coil maker's data. If you're unsure about a coil you've got, ask us before you crank the engine.
