What dead time is
A fuel injector is an electromagnet holding a valve shut. When the ECU energizes the coil, the magnetic field has to build and the valve has to lift before any fuel flows. That delay, from the moment the coil is switched on until fuel actually starts moving, is dead time. You'll also see it called injector latency or injector lag time.
The ECU adds dead time on top of the pulse width it calculates, so the injector is open for as long as the tune intends. If the value is too short, the engine runs lean. Too long, and it runs rich.
Why it matters most at small pulse widths
At full load the injector is open for a long time and a small dead time error barely registers. At idle and light cruise, pulses are short, and the same error becomes a big chunk of the total. That's why wrong dead time data shows up as an idle that won't settle, or fueling that goes off as battery voltage changes.
What it depends on
Every injector model has its own dead time. It changes with several things, but the two that are usually measured are:
- Battery voltage: lower voltage means the coil takes longer to pull the valve open.
- Differential fuel pressure: the pressure the valve is working against.
Where to get the numbers
Like flow rate, dead time should come from the injector manufacturer or supplier, not from guessing. Enter their data into this table as accurately as you can. It's the foundation for accurate fueling across the whole load range. Pair it with correct injector flow, and see the short pulse width adder for very small pulses. Our longer injector dead time guide goes deeper. If your injectors didn't come with data, ask us.
