In my last post, I detailed how the relays in the ECU system allow the system to flip to a default engine map. This lets the team keep running, even when something fails, and it decreases the chances of the ECU doing something that blows up the engine. Here’s a short explanation of what exactly an ‘engine map’ is and what it does.
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Good basic explanation. The ECU runs in either closed loop or open loop mode. In closed loop it is receiving info from all inputs (sensors) within correct parameters, and so follows the closed loop map.
If some sensors fail, or go outside the normal operational data parameters, such as a temperature, oxygen sensor, or air flow sensor (MAF) the ECU goes into open loop mode, ensuring the engine wont go way too lean or way too rich, for example, but follows a “limp home” mode for ignition timing, and injector pulse width..
There however is nothing it can do if a cam sensor or crank sensor goes bad, it will lose all timing reference for injector PW and ignition spark events and the engine will not run.
And if the TPS,( throttle position sensor) fails completely, the engine will either die or remain at idle only,, depending on the ECU programming.