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Why lean on hot restart?

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I saw this mentioned in the startup tuning webinar and have observed it myself.

Why does a heat-soaked re-start result in a temporary lean condition?

The temp sensor is reflective of the manifold/engine bay temp, not the airflow. You need some mass flow to draw the heat out of the sensor.

What if it's not temp sensor compensation?

Hot fuel is less dense (contains less energy) than cool fuel, and if you're very unlucky the fuel might be so heatsoaked that it boils and you experience 'vapor lock'. This video shows fuel boiling on an old car with a carburetor, those setups run lower fuel pressure which should be more susceptible to vapor lock than fuel injected setups [url=https://www.youtube.com/watch?v=cadNfSNi_Oc]https://www.youtube.com/watch?v=cadNfSNi_Oc Some OEM engines used vacuum solenoids to run a bit higher fuel rail pressure on hot restarts. If you have a return-style fuel system try running the fuel pump for longer before starting the engine. If not, try adding more fuel to the cranking and after-start tables, hot restarts may need longer injection pulses (which may not actually be more fuel mass) compared to a normal warm engine.