O2 / Lambda Sensor¶
Measures the mixture in the exhaust so the ECU can trim fuelling toward target. In Engone it behaves like a wideband — but it reports with a delay.
What it is¶
The oxygen sensor sits in the exhaust and reports the burned mixture as a lambda value. It's the feedback signal that closes the fuel loop — the ECU's only direct measurement of whether it actually hit the mixture it aimed for.
The sensor behaves like a wideband: it reads the full range, not just near λ = 1. That's what lets you read and tune WOT mixtures, which sit well away from stoich.
It reports with a delay. The reading is the sum of a 0.12 s sensor lag and two engine cycles of exhaust transport — about 0.4 s at idle and about 0.16 s at 6000 RPM, clamped to 0.05–0.8 s. During any fuel cut it reads about 5 (no fuel), and closed loop shuts.
Background: narrowband sensors
A real narrowband sensor is accurate only right around λ = 1.0. It can tell rich from lean near stoich but can't quantify how rich or lean elsewhere. That's why tuners fit a wideband.
Why it matters¶
The O2 sensor is what makes closed-loop fuel trim possible. Without it, the ECU is flying blind on the open-loop tables. The delay has two consequences: the λ readout looks into the past, and closed loop can only trim slowly and must ignore transients.
How to tune it¶
Use the live lambda readout as your truth source: compare measured λ to the target for the current cell, and correct the VE table where they disagree. Remember the reading lags what the engine is doing now, so hold a steady operating point.
Rule of thumb
Tune VE so that measured λ matches target with closed-loop disabled — then closed-loop only has to make tiny corrections.
In the game¶
The λ DEVIATION panel in the left readouts shows the measured mixture: λ target, λ actual,
the difference Δ, and a centre-zero bar. It's your primary feedback for all fuel tuning. See
Air–Fuel Ratio & Lambda.