Ignition · wasted spark · COP
Wasted spark vs coil-on-plug wiring diagrams
Both layouts do without a distributor. Wasted spark fires two cylinders from one coil every revolution; coil-on-plug gives every cylinder its own coil. The wiring differs in the number of ECU outputs, in cam sync, and in what kind of coil you use.
Open the editor · ▶ Run the live demo
Side by side (4 cylinders)
| Wasted spark | Coil-on-plug | |
|---|---|---|
| Coils | 2 double-ended coils (or a 2-channel pack) | 4, one per plug |
| ECU ignition outputs | 2 (cylinders 1+4 and 2+3) | 4 for sequential, or 2 if paired |
| Cam sensor | Not needed | Needed for sequential |
| Spark | Every revolution, one on the exhaust stroke | Once per cycle, when needed |
Coil power and control
- All coils share switched +12 V from the ignition or the main relay, through a fuse sized for all of them.
- A plain coil (two low-voltage pins) is switched to ground by an igniter — a power transistor in the ECU or a separate module.
- A “smart” coil has the igniter built in: +12 V, ground, and a 5 V logic trigger (IGT) from the ECU.
- Driving a plain coil from a logic output does nothing; driving a smart coil from an igniter output can burn it. The ECU output type must match the coil.
COP coils in wasted-spark mode
Without a cam sensor you can still use coil-on-plug coils: the ECU fires them in pairs, two coils per output. You lose sequential timing but keep the better coils. Check that the ECU output can drive two smart-coil inputs at once.
Compare them in WireForge
- Open the “ECU fuel injection” demo or place an ECU module.
- Add Ignition Coil devices for a plain coil, or Ignition Coil with Igniter (COP) for a smart coil.
- Feed +12 V through a fuse, wire each coil’s control pin to an ECU ignition output, and set Engine speed.
- Simulate: the ECU fires the coils in turn; if the output type does not match the coil the simulator says so.
Questions
Does wasted spark wear plugs faster?
Slightly — one plug of each pair fires with reversed polarity. With modern plugs the difference is small.
Can I run a 4-cylinder COP setup with only two outputs?
Yes, in wasted-spark mode: pair the coils of cylinders 1+4 and 2+3 on one output each, if the output can drive two coils.
How do I know if my coil has an igniter?
Usually three or four pins (+12 V, ground, trigger, sometimes a feedback pin) means a built-in igniter; two low-voltage pins means a plain coil. Confirm with the part number.