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How the ECM Affects the Fuel Delivery System

A vehicle’s ECM controls the engine by receiving data from certain sensors, then sending commands to other sensors and systems, including the fuel delivery system. The PROM – the main memory chip – holds values programmed by the manufacturer. These values are used to compare data from sensors to ensure the proper operating environment, including when to light off the spark plug and how much fuel to send.

Starting the Engine

You need fuel to start the engine. The ECM reads the information from the PROM, then pulses the injectors, all in less than a second. As soon as it pulses the injectors, the ECM activates the fuel pump for two seconds to prime the fuel delivery system. If your vehicle’s fuel pump is on the loud side, this is the buzzing you hear when you first turn the key on.

After this, the ECM waits for signals from various sensors so that it can figure how much fuel the engine needs to start. It reads the position of the crankshaft from the crankshaft sensor, the temperature of the engine from the coolant temperature sensor and the amount of pressure in the intake manifold or the amount of oxygen in the air (depending on whether your vehicle has a MAP or MAF sensor).

Open Loop Run Mode

When the engine first starts, it is cold, thus it needs a richer mixture – more fuel. This is referred to as open loop. If the engine RPM is above 400 and the engine is cold, the ECM ignores the oxygen sensor values to create the air-to-fuel mixture. As soon as the engine warms up, it goes into closed loop and accepts information from the oxygen sensors to help determine the air-to-fuel mixture.


For those who are familiar with the workings of a carburetor, you know that the accelerator pump provides an extra squirt of gas upon acceleration so the engine doesn’t stumble. Just because a vehicle has fuel injection doesn’t mean that doesn’t have to happen – in fact, it must happen to keep the engine from stumbling.

The ECM checks the values from the manifold absolute pressure (MAP) sensor and the throttle position sensor. It uses the values to determine whether it should “kick on the accelerator pump,” so to speak. This is called an “accel enrich” event. Using the values from the MAP and TPS, the ECM determines how much extra fuel is needed to keep the engine from falling on its face during acceleration.

This only touches on some of the functions the ECM plays in the fuel delivery system. The part of the ECM that governs fuel injection must be working properly for the engine to work properly. All sensors must also work properly for the fuel delivery system to function properly.

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