If we compare the engine to the “heart” of a car, then the car’s “brain” should be the ECU. What is an ECU? How does it work? This article provides a detailed analysis.What is an ECU? ECU has two full names: Engine Control Unit and Electronic Control Unit. It is easy to see that the former refers to the “engine control unit” while the latter is the “electronic control unit.” These are two concepts that can be easily confused, and today we will primarily analyze the “Engine Control Unit.”
1 The Emergence of ECU
Before 1967, the fuel supply system of gasoline engines was managed by carburetors, which is completely different from today’s electronic fuel injection engines. Carburetors utilize the pressure difference before and after the throttle to draw fuel, which not only fails to accurately control the fuel supply but also restricts the improvement of vehicle performance and environmental protection. Companies like Bosch developed electronic fuel injection systems, with the earliest BOSCH electronic injection system being D-Jetronic, followed by K-Jetronic and L-Jetronic. After the introduction of electronic technology, BOSCH developed several electronic management fuel injection systems, among which KE-Jetronic is widely used today. Although the product names vary among companies, their structures are quite similar.The working characteristic of the electronic injection system is to inject fuel in a “quantitative and timed” manner. The engine requires a certain amount of fuel to be injected at a specific moment, which is directly related to the engine’s speed, air flow, and various other parameters such as water temperature and oil pressure. How are so many parameters processed and how does the injection system receive fuel injection commands? This is where the engine control unit comes into play, and thus the ECU was born.
2 Working Principle of ECU
Like a regular microcontroller, the ECU consists of a microprocessor, memory, input/output interfaces, analog-to-digital converters, and integrated circuits for shaping and driving. The role of the ECU is to calculate the vehicle’s operating conditions through various sensors, thereby controlling multiple parameters such as ignition timing, air-fuel ratio, idle speed, and exhaust gas recirculation. It operates within a temperature range of -40 to 80 degrees Celsius and can withstand significant vibrations, making the probability of ECU failure very low. Additionally, the ECU has self-diagnostic and protection functions; when a fault occurs, it can automatically record the fault code in memory and adopt protective measures by reading alternative programs from its inherent routines to maintain engine operation, allowing the vehicle to reach a repair shop.How does the ECU work? Simply put, it is a command process akin to that of a general: “thinking,” “commanding,” and ultimately “confirming.”The “reconnaissance” is completed by sensors, which are responsible for monitoring the entire engine. A single engine can have dozens of sensors, including throttle position sensors, crankshaft speed sensors, oxygen sensors, crankshaft position sensors, camshaft position sensors, intake temperature sensors, water temperature sensors, and knock sensors, which are the most basic sensors in a car engine. Sensors are ubiquitous; they collect relevant information and transmit it to the ECU in the form of electrical signals. After being converted into digital signals by the A/D converter, the ECU processes the data to determine the current operating state of the engine, which constitutes the “thinking” process of the ECU.What is the standard for this “thinking” process? Computers do not possess thoughts; they rely on programs stored in ROM. This is akin to software. When data is input into the ECU, the ROM program compares the existing data with the collected signals to derive adjustment methods. This entire program is the soul of the ECU, and its development is based on extensive experimental data, often requiring bench tests and road trials to establish. Typically, tuning shops modify the ECU program by rewriting or revising the ROM program to change the ECU’s calculation criteria.Let’s delve deeper into this process:The amount of fuel supplied is calculated based on the duration of fuel injection from the injector. The fuel computer (ECU) calculates the required fuel injection time based on air flow, engine speed, and compensation signals provided by various sensors, using the originally set fuel supply program, which can be represented graphically.The fuel injection time calculated by the ECU is the sum of the “basic injection time,” “compensation injection time,” and “ineffective injection time,” measured in microseconds (ms), where 1 ms = 0.001 seconds. The amount of gasoline injected by the injector in a unit time is determined by the size of the injector’s diameter and the injection pressure.1. Basic Injection TimeThe basic injection time is determined by the intake volume (referring to weight) and engine speed. When you press the accelerator pedal, you control the opening angle of the throttle; the larger the opening, the greater the intake volume. The fuel computer calculates the required fuel amount and corresponding injection time by comparing the intake volume measured by the air flow meter with the preset fuel supply program at the current engine speed.2. Compensation Injection TimeCompensation injection, commonly referred to as “acceleration,” is determined by various sensors that detect the engine’s current operating conditions and load. After sending the signals to the computer (ECU), it calculates the additional fuel required to maintain stable and smooth engine operation. The setting of the compensation injection program is a complex task and varies from vehicle to vehicle.Generally, the compensation injection program includes the following items: cold start compensation, warm-up compensation, idle restart compensation, high-temperature compensation, acceleration compensation, high RPM/high load compensation, theoretical air-fuel ratio feedback compensation, and fuel cut control.3. Ineffective Injection TimeThe time delay from when the injector is energized to when it fully injects fuel is called “opening delay,” while the time from when the coil is de-energized to when it completely stops injecting fuel is called “closing delay.”Since the opening delay is longer than the closing delay, the actual fuel supply will be less than required. The difference between the opening delay and closing delay is referred to as “ineffective injection time.” To obtain the correct fuel supply, the ineffective injection time must be accounted for, meaning that after calculating the fuel supply, the amount of fuel injected during the ineffective injection time must be added to match the desired amount. Therefore, ineffective injection time can also be considered a part of compensation injection.Of course, the ECU is not static; another function of the memory is akin to an airplane’s “black box,” capable of recording vehicle operation data. Many ECUs have a “learning” capability, where the memory continuously records data during driving, forming the ECU’s learning program to provide optimal control states that adapt to the driver’s habits. This program is also known as the adaptive program. However, since it is stored in memory, similar to error codes, if the battery is disconnected and power is lost, all data will be lost. The ECU can continuously learn from the recorded data to better understand the driver’s driving style, making it more user-friendly. Of course, in the event of a fault, information can also be retrieved from the memory to assist in repairs.After completing the “thinking” process, the next step for the ECU is to “command.” The components controlled by the ECU include the injectors, which adjust the fuel amount and timing, while the fuel pump is responsible for supplying fuel; the ignition controller and ignition coil are also controlled by the ECU for ignition timing, etc. After this, the ECU needs to receive data again to confirm the end of a closed-loop control.With technological advancements, the ECU has taken on more responsibilities. Technologies like i-VTEC, which involve variable valve timing, require additional camshaft position sensors and calculations by the ECU to adjust the camshaft phase. Especially in systems like BMW’s Double-VANOS, which features continuously variable valve timing, the ECU must perform precise calculations to control its phase and valve lift. Currently, in some mid to high-end vehicles, ECUs are not only applied to engines but can also be found in many other systems. For example, anti-lock braking systems, four-wheel drive systems, active suspension systems, airbag systems, and automatic transmissions all require separate control systems. The increasing number of ECUs in vehicles means that many new devices require ECU management, and the traditional “Engine Control Unit” can no longer meet the demands of modern development, becoming just one module of the overall vehicle control system. Therefore, today we prefer to refer to the ECU as the “Electrical Control Unit,” i.e., the electronic control system. As the automation and electronicization of vehicles increase, the number of ECUs will continue to rise, and the wiring will become increasingly complex. To simplify circuits and reduce costs, the information transfer between multiple ECUs in a vehicle will adopt a technology known as multiplex communication network technology, forming a network system of the vehicle’s ECUs, which is the CAN data bus.
3 ECU Upgrades
1. Feasibility of ECU ModificationECU manufacturers are all international multinational companies, such as BOSCH, SIEMENS, and MM, and their products are sold worldwide. Due to differences in gasoline quality, temperature, atmospheric pressure, humidity, and engine types in each country, the ECU program software must be set to meet the conditions of each country. Modern vehicles must adapt to various weather and environmental conditions (such as high altitudes, deserts, extreme cold, and poor-quality gasoline) and different driver requirements, while also ensuring that they can operate smoothly and meet strict emissions and fuel consumption standards. Therefore, in most cases, the original ECU program is a compromise that meets many conditions, allowing for some flexibility for modifications. Additionally, when manufacturers tune engine parameters, they generally consider that the engine should operate normally even in the most adverse conditions or when not maintained for long periods. This means that manufacturers always set engine output conservatively, so as long as the owner ensures regular maintenance, they can achieve greater output by recalibrating engine parameters for an extraordinary driving experience.For example, regarding the air-fuel ratio (AFR), the factory programmer may set the AFR to be leaner (less fuel, more air) under certain driving conditions (such as cruising) to reduce fuel consumption and pass fuel economy tests in some countries. However, during other times, the factory ECU’s AFR is generally set at 1:14.7, as this is the easiest ratio to meet emissions standards. But for most engines, the maximum power is achieved with a richer mixture (more fuel, less air). Similarly, to broaden the fuel adaptability of the vehicle (different fuel grades in different regions), the factory-set ignition advance angle is generally suitable for lower-grade fuels (the engine outputs different power at different ignition advance angles). This means that the current ignition advance angle of your engine may not be optimal for the fuel grade you are using. If the original program can be modified to favor performance, it can increase horsepower by about 5-8%, and some turbocharged vehicles can achieve up to 15% more power.2. Methods of ECU ModificationECU chip modification: When a manufacturer designs an engine, the originally set fuel supply program is burned into the ROM. This program is usually a product of compromises regarding fuel consumption, emissions, and smooth operation, and it is unchangeable. Because it is unchangeable, if you want to alter the fuel supply program, you must switch to a different mode of ROM. Typically, professional tuning shops provide modified computer chips for various vehicle models. During modification, the original chip is removed (usually the factory fuel computer’s ROM is directly soldered onto the circuit board), an IC socket is soldered on (making future replacements easier), and the modified chip is inserted. The resulting fuel supply program remains fixed; it merely corrects the original program, with one important aspect being the ability to delay or even eliminate the fuel cut control time in the compensation injection program.It is important to note that each modified chip has its set applicable conditions (i.e., the degree of modification). When modifying, you must choose a chip that closely matches your vehicle’s modification status to achieve the best results; otherwise, it may backfire. The selection of chips should only be done in consultation with experienced tuning shops. One chip corresponds to one fuel supply program, and clever readers might wonder: what if two or three chips are installed? Indeed, in the past, some tuning shops in the country installed two or three different fuel supply mode chips on the same circuit board, allowing the driver to switch between the desired fuel supply modes using an external switch, similar to switching between P, E, and S modes in an automatic transmission to meet different driver needs.ECU computer programming: This is a more specialized aspect of ECU system modification, and the most familiar in the domestic tuning community is HALTEC computers. With this computer, the owner can set the optimal fuel supply program according to the degree of modification of their engine, in conjunction with measurements from an air-fuel ratio meter, allowing for arbitrary changes to the basic injection program and various compensation injection programs using a laptop. Its greatest difference from chip modification, and its biggest advantage, is that if the engine undergoes further modifications later, and the original fuel supply program becomes incompatible, it can be immediately resolved through program adjustments. After computer programming, the original fuel supply program becomes obsolete, but higher-level computers can retain all the functions of the original sensors, meaning that various fuel compensation programs can still operate normally and be modified without sacrificing smooth operation and practicality for higher performance.The greatest difficulty in modifying a programmable ECU does not lie in installation but in the setting and optimization of the fuel supply program. This often requires experience and instruments, and through continuous testing, it can be achieved. Currently, tuning shops typically select a basic mode as a foundation and then gradually adjust it through actual operation and testing until satisfied.3. Common Issues During ECU ModificationUnlike other mechanical systems, the functions and working principles of the ECU are “invisible,” and most auto repair shops, even 4S dealerships, do not understand or cannot repair or resolve ECU-related issues, creating a sense of mystery around the ECU. Below, we will discuss several common issues during ECU flashing.1) Use the Original ECU or a Newer ECUFor general civilian modifications, I personally prefer using the original ECU for modifications. This is because the original ECU is very powerful, and its program has been developed through long-term data accumulation and countless tests by the manufacturer’s engineers. It can protect the engine under any circumstances without generating fault codes or warning lights, and it will not cause conflicts with other systems like ABS, traction control, and anti-theft systems. Additionally, it will not delete any important functions from the vehicle. On the other hand, the modification cost is relatively low.2) Degree of ECU Modification and Tuning StyleFrom a performance modification perspective, ECU modification is an indispensable step. The ECU can help the engine achieve optimal mechanical functionality, but it cannot exceed the limits originally designed. For example, when professional racing teams develop racing engines, they first design the camshaft, pistons, connecting rods, and other mechanical components, determining the engine’s compression ratio and maximum RPM before considering the ECU. Without a powerful engine, no matter how capable the ECU is, it is futile. Therefore, regarding the tuning methods for ECU programs, unless used for racing, the focus is generally not solely on maximizing horsepower at full throttle. More attention is paid to the vehicle’s acceleration capability and throttle response at low to mid RPMs, as civilian vehicles rarely operate at full throttle and maximum RPM. Thus, the emphasis is on achieving smooth and progressive horsepower and torque curves in the 2000 RPM to 4000 RPM range, ensuring that the driver feels the throttle is particularly responsive and powerful. The maximum horsepower figure may attract attention in promotional materials, but in real-world conditions, no one enjoys driving a car that accelerates unsmoothly. Therefore, it is unnecessary for modified street cars to achieve performance levels comparable to racing cars; a more accurate understanding should be whether such modified products can improve power output while ensuring vehicle safety and meeting practical needs, including smoothness during starts, mid to high RPM extension, and acceleration capability. Meanwhile, the data and trend graphs from dynamometer tests, along with the driver’s actual sensory experience, serve as important evidence for validating the quality of the product and the effectiveness of the modifications!3) Will ECU Upgrades Affect Vehicle Lifespan and Safety?Many people may have concerns about whether ECU upgrades will affect the vehicle’s lifespan and safety. In fact, there is no need to worry; flashing the ECU is merely a comprehensive optimization of the vehicle’s driving computer data, not an attempt to maximize a single performance indicator by unleashing the engine’s full capabilities. The optimization is based on ensuring longevity, economy, and safety, providing the vehicle with a safe operating margin and creating the most comfortable operating environment for the engine. However, in some cases, due to cost and technical levels, some car enthusiasts may resort to installing components commonly referred to as “secondary air intake” or “fuel addition” to increase the amount of fuel and air entering the engine. These components essentially bypass the original sensors or alter sensor voltages to “deceive” the ECU, causing it to unknowingly change the air-fuel ratio entering the engine, improving performance under certain conditions. This incomplete modification approach can lead to side effects and even safety issues, while the proper ECU modification method, although more costly, can avoid many adverse side effects.4) Differences in ECU Settings Between Street Cars and Racing CarsECU settings are generally divided into two types: street cars and racing cars. For racing cars, since the fuel, venue, and driver factors are predetermined, the computer settings focus on how to respond to changing weather, temperature, and other environmental factors. Street cars, on the other hand, are much more complex, as there are no restrictions on driving time, and fuel quality can vary, even among high-quality fuels from different gas stations. Compared to racing cars, street car modifications must consider safety factors, so the computer settings must retain some flexibility. After comprehensively considering the driver’s driving style and vehicle characteristics, the settings can be made. Moreover, even under the same conditions and with the same vehicle, variations can occur, so using the same data for settings may not yield the best results.5) Points to Note When Flashing the ECUMany car owners focus solely on horsepower without considering torque, which is a common occurrence. In fact, modifications should not be blindly aimed at maximizing horsepower; it is essential to clarify the vehicle’s intended use and the owner’s driving habits before modification.For tuning shops, when modifying the ECU, it is advisable not to focus solely on fuel injection timing but also to ensure that fuel supply is adequate. Attention should also be paid to the arrangement of ignition timing, as the ignition advance angle is crucial. Additionally, any hardware added to the vehicle must be understood in terms of its characteristics, so that the ECU can be adjusted accordingly to achieve optimal performance.Furthermore, if the engine uses a high-angle camshaft, as it alters the timing of valve openings and closings, programming adjustments become even more challenging, requiring precise calculations and tuning. The ability to fully utilize the performance of modified parts is entirely dependent on the ECU’s adjustments, but changing the engine’s characteristics through ECU data modification is a very difficult task.
(Images and text sourced from the internet)
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