Warmup Enrichment¶
Sustained extra fuel held while coolant is below operating temperature, tapering to neutral as the engine warms.
What it is¶
After the brief after-start period decays, the engine is running but still cold. Warmup enrichment is the long, steady correction that stays active the whole time coolant is below operating temperature, tapering to 1.0× at around 80 °C.
Unlike cranking and after-start, warmup enrichment is governed purely by coolant temperature (CLT/ECT), not by time — it stays rich as long as the engine is cold, however long that takes.
Why it matters¶
A cold engine's intake and combustion chamber still suffer from poor fuel vaporization and ongoing wall-wetting until everything reaches operating temperature. Warmup enrichment keeps the mixture combustible and the idle stable across that whole window.
- Too little → lean, hesitant running and possible stalling while cold.
- Too much → a rich, lazy warmup that wastes fuel and can foul plugs.
How to tune it¶
Shape the curve against coolant temperature: richest where the engine is coldest, smoothly reaching neutral as it nears operating temperature. The warm end must return to 1.0× or the engine will run rich even when fully warm.
Rule of thumb
Drive a full warmup cycle watching measured lambda. Trim the curve so the mixture tracks its target the whole way up to temperature.
Watch out
If a fully warm engine runs rich at idle, check that the warmup curve actually reaches 1.0× — a curve that ends at, say, 1.1× will richen every warm idle.
In the game¶
The warmup curve is on the Fuel page, plotted against coolant temperature. Its multiplier should visibly fall to 1.0× as the coolant gauge reaches operating temperature.