ИСПРАВЛЕНИЕ ГОРЯЧЕГО ЗАПУСКА

What is the Hot Start Fix?

The Hot Start Fix is an ECU calibration service that resolves extended cranking and difficult starting when the engine is warm or at operating temperature. This is a well-known issue on certain engine platforms where the factory ECU calibration does not adequately compensate for the different fuel vaporization characteristics and air density conditions present in a hot engine. The result is an engine that starts instantly when cold but cranks for several seconds — or requires multiple attempts — when restarted after a short stop.

This is not a mechanical fault. It is a calibration issue in the ECU software, and it can be resolved with a targeted adjustment to the hot-start fueling and cranking parameters.

What Causes Hot Start Problems?

When an engine is shut off at operating temperature, heat soak causes fuel in the injectors and fuel rail to vaporize. On direct injection engines, high fuel rail pressure can also drop during the soak period. When the driver attempts to restart the engine, the ECU applies its standard cranking fuel map — which may not deliver enough fuel, or may deliver fuel at the wrong timing, to account for the vaporized fuel and reduced rail pressure conditions.

On some platforms, the issue is compounded by inadequate cranking speed targets, insufficient priming pulse duration, or incorrect fuel pressure compensation during hot restart. The factory calibration may work acceptably in mild climates but fail in hot weather or after the engine has been run hard and heat-soaked thoroughly.

How Does the Hot Start Fix Work?

Our engineers modify the ECU calibration to improve hot-start behavior through several targeted adjustments. The cranking fuel enrichment maps are recalibrated to deliver the correct fuel quantity for hot-engine conditions. Fuel rail pressure targets during cranking may be increased to ensure adequate atomization. Cranking speed and duration parameters are optimized to ensure the engine fires reliably on the first or second revolution.

On platforms with variable valve timing, the cam phasing during cranking may also be adjusted to improve cylinder filling at hot-start conditions. The specific adjustments depend on the engine platform and the root cause of the hot-start issue on that particular ECU calibration.

Which Vehicles Are Affected?

Hot start issues are most commonly reported on certain BMW (N20, N55, B48, B58), VAG (EA888, EA211), and PSA (EP6, THP) platforms, though the problem can occur on any engine where the factory calibration has insufficient hot-start compensation. Both petrol and diesel engines can be affected, though the issue is more prevalent on direct injection petrol engines due to their sensitivity to fuel vaporization conditions.

Our Process

Send us your original ECU file and describe the hot-start symptoms you are experiencing. We will analyze the cranking calibration and apply the appropriate corrections for your platform. Files are typically delivered within 30–60 minutes, with checksum correction included.