Petrol Tuning Fundamentals

Petrol Tuning Fundamentals:

We'll be learning about the following subjects right now: 

• What is an injection system and how does it work?
• Electronic Control Unit in Engine Management
• Torque based engine management system
• What is the Air-Fuel Ratio, and why does it matter in petrol engines?
• What is Lambda, and how do AFR and Lambda relate to each other?
• What impact does the air-fuel ratio have on engine performance?
• What effect does the Spark advance have on engine performance?

In fact, until now learning how to tune EFI engines has been notoriously difficult. It's a unique industry as there's no formal qualification path that you can take to become a qualified and recognized EFI tuner. This makes it harder if you've got an interest in EFI tuning and want to learn more. Tuning is simply a science and it's a science you can learn and master with the help of this WinOLS Training Course and this ECM Titanium training course. The CaracalTech Petrol tuning fundamentals course teaches you the core principles behind the engine operation, how the ECU works, and how to calibrate the fuel and ignition timing, even on engines that you're tuning for the first time. You'll also learn how compensation tables work in the ECU and how to correctly configure them. Furthermore, you'll learn how interpolation works and the fuel and ignition tables and learn how to correctly configure your tables for maximum accuracy without making more work for yourself. 
First of all, we want to give you a preview of what is going on in our EFI course:

1. What is an Injection System and How Does it Work?

An appropriate fuel injection system provides an accurate AFR, which allows for great fuel economy and permits emissions control systems to operate properly. This basically involves maintaining an accurate air-fuel ratio which provides: Engine operates well even at low temperatures and the vehicle adapts well to a broad range of altitudes and environmental temperature and also Engine speed (including idle and redline speeds) is precisely regulated. There are three main components to all fuel injection systems: Injectors, ECU, and fuel pump are the three fundamental components. The engine control unit is normally in charge of fuel metering and injection valve actuation in advanced engines. As a result, the fuel injection pump only needs to provide injection pressure rather than metering the fuel. 

1.1. Electronic Control Unit in Engine Management:

The proper quantity of fuel is injected into the engine, which is one of the most important aspects of the fueling system. Because so many factors influence fueling, such as engine coolant temperature and exhaust temperature, we'd want to provide an example to explain how complex the fuel system in an ECU is. 
You will learn more about ECU fuel control as you become more acquainted with this technology. The engine's control algorithms are highly complex. The software must allow the vehicle to fulfil emissions standards for 100,000 miles, meet EPA fuel efficiency standards, and protect engines from misuse. There are also a slew of other requirements to meet. In order to determine the pulse width for specific operating conditions, the engine control unit employs a formula and a huge number of lookup tables. The equation will be made up of a number of factors multiplied by one another. Lookup tables will provide many of these factors. We'll go through how to calculate the fuel injector pulse width in a simple way. Our equation will only contain three factors in this example, although a genuine control system may have a hundred or more. 

Pulse width = (Base pulse width) x (Factor A) x (Factor B)

The ECU searches up the base pulse width in a lookup table in order to calculate the pulse width. The manifold absolute pressure is used to compute base pulse width, which is a function of engine speed and load. Assume the engine is running at 2,000 RPM with a load of 4. We find the number at the intersection of 2,000 and 4, which is 8 milliseconds. 

A and B are sensor-derived parameters in the following cases. Assume A is the coolant temperature and B is the oxygen level. The lookup tables tell us that Factor A = 0.8 and Factor B = 1.0 if the coolant temperature is 100 and the oxygen level is 3.

Because we know that base pulse width is a function of load and RPM, and we know that the pulse width = (base pulse width) x (factor A) x (factor B), the overall pulse width in our case is: 

8 x 0.8 x 1.0 = 6.4 milliseconds

1.2. Torque Based Engine Management System:

This represents a new method in the control unit world today. Now, instead we are going to analyze the main strategy for the control of turbo-petrol engines. This strategy is based on the control and monitoring of the engine torque. The torque based control strategy arrows  From the need to have more efficient and responsive engines, we are always checking their missions. This strategy directly manages engine performance by controlling air, fuel and spark advance. We have seen that no matter how accurate the MAF and MAP sensors or the MICROCONTROLLER doing the calculations are. The previous strategies do not have the ability to determine what is really going on in the engine in terms of performance. In addition, automotive groups have an increasing need to certify that the emissions produced by the performance are identical for all the mass-produced cars. Therefore, it became necessary to introduce a new parameter on which to base the entire control strategy, they would make it possible to represent engine performance by managing fuel and ignition advance to air regulation. ECU developers have identified all of these with engine torque. If you are interested in features, click here.

2. What is The Air/Fuel Ratio, and Why Does it Matter in Petrol Engines?

Internal ignition engines generate power by igniting fuel and oxygen from the air. Certain amounts of fuel and air must be delivered in the combustion chamber in order to ensure the combustion process. This means that the air-fuel ratio must be within a certain range to form the ignition in the internal combustion engine. 
The air-fuel ratio is one of the most significant tuning and remap concepts. The mixing ratio or proportion of air and fuel supplied to the engine through the fuel system is known as the air-fuel ratio, or AFR. Stoichiometric air-fuel ratio is the optimal theoretical air-fuel ratio for full ignition. The stoichiometric air-fuel ratio for a petrol engine is roughly 14.7:1. This means that 1 gram of fuel requires 14.7 grams of air to totally burn. Additionally, even if the AFR is not stoichiometric, combustion still continues. Furthermore, When all of the fuel is burned, complete combustion occurs, and there will be no unburned fuel in the exhaust gas. However, combustion will never be complete due to changing conditions and a limited combustion time. As a result, this ratio will vary depending on the engine's operating conditions. 
The air-fuel mixture is considered lean when the air-fuel ratio exceeds the stoichiometric ratio. The air-fuel mixture is described as rich when the air-fuel ratio is less than the stoichiometric ratio. For a petrol engine, an AFR of 16.5:1 is lean, whereas 13.0:1 is rich. You might be asking “Why the air-to-fuel ratio isn't a constant amount rather fluctuates?”. The variable air-to-fuel ratio refers to the fact that the engine operates under a variety of conditions, each of which requires a different AFR. Generally, lean and rich fuels have distinct qualities, and they are employed in different engine conditions based on those characteristics.
Engine performance, emissions, fuel economy, and lifetime are all affected differently by lean or rich fuel. Low fuel consumption, poor engine performance, high temperature, generation of nitrogen oxides, and rough idle are some of the characteristics of lean fuel. Rich fuel can cause excessive fuel consumption, improved engine performance, high carbon monoxide emissions, a pungent or rotten egg smell, carbon deposits on valves and pistons, and other issues. As a result, the engine's AFR must change frequently.
The lowest AFR for the combustion process in a petrol engine is roughly 6:1, while the maximum may reach up to 20:1.

There are numerous AFR ratios, which are typically as follows:

• 6      AFR - Rich Burn Limit (engine fully warm)
• 9      AFR - Black Smoke Low Power
• 11.5 AFR - Best Rich Torque at Wide Open Throttle (WOT)
• 12.2 AFR - Safe Best Power at Wide Open Throttle (WOT)
• 12.8 AFR - Lean Best Power at Wide Open Throttle (WOT)
• 13.3 AFR - Lean Best Torque
• 14.7 AFR - Stoichiometric Air/Fuel Ratio Value
• 15.5 AFR - Lean Cruise
• 16.5 AFR - Usual Best Economy
• 18    AFR - Carbureted Lean Burn Limit
• 22    AFR - EFI Lean Burn Limit

✅As you can see, an engine must get the necessary AFR in other working areas in order to perform well in different conditions. Although, these numbers are indicative and do not apply to all engines or working conditions.

2.1. What Exactly is Lambda?

The Greek letter Lambda can also be used to express the Air Fuel Ratio. Lambda is obtained by dividing the actual AFR by the stoichiometric AFR. 
Lambda =  The lambda equals one when the real AFR equals the stoichiometric AFR. That is, the lambda of AFR 1 = 14.7 / 1

Lambda = (14.7/1) ÷ (14.7/1) = 1.0

If, for example, the air-fuel ratio is 13.1, we must divide 1314.7 to find the value of lambda. The lambda value is 0.88.
If the AFR is equal to 16, the lambda is 1.088, according to what we said. Therefore, we can conclude from these calculations and relationships that:
So, a lambda more than one, such as 1.2, represents a leaner air fuel ratio, whereas a lambda less than one, such as 0.88, represents a richer air fuel ratio.
In other words, when we say AFR 14.7/1, we're talking about 14.7 units of air and one unit of fuel (lambda 1).
Now, if this ratio is 13.1, it means that there is less air in the mixture, implying that the fuel is richer.

2.2. What Impact Does The Air/Fuel Ratio Have on Engine Performance?

According to our explanations, the engine maximum power can be achieved at AFR 12.6 or lambda 0.86 in the air-fuel ratio graph. If you look closely, you'll notice that the lambda is 0.86 less than one,  which is in the rich area. You can see that the engine power has reduced on the right side of the diagram.
We want to teach you about the relationship between AFR and different pollutants. In this case, we can say that if AFR is in the rich range, i.e. The lambda value is smaller than 1,  where the maximum engine power is obtained in this area, the amount of CO and HC has increased. However, NOX decreases. The low combustion chamber temperature and rich air-fuel ratio reduce NOX emissions. But when the AFR is adjusted to stoichiometric, HC and CO fall to their lowest levels, while NOX increases to its maximum. The higher temperature of the combustion chamber is the cause of the increase in NOX.
Now, CO and NOX are lowered, but HC is raised, at AFR 15.5 or 16. which are the best values to obtain the optimum fuel consumption.

3: What is Requested Engine Load?

Requested Engine Load (often called driver requested load) is a target value set by the ECU based on the driver’s input (mainly the accelerator pedal position) and various other factors like vehicle speed, gear, and environmental conditions.

It represents the desired engine output, expressed as a percentage of full engine load (airflow or torque).

The ECU uses this value as a reference to calculate how much air and fuel to supply, and how to adjust boost, ignition timing, and cam phasing accordingly.

3.1: Role of Requested Engine Load in ECU Remapping:

When tuning an ECU, the Requested Engine Load Map plays a foundational role in how much torque the engine is allowed or asked to produce.

Here's why it's important:

• It defines how aggressive or conservative the throttle response is.
• It sets the upper bound for actual engine load (i.e., air mass and torque output).
• It's the first step in the torque request chain, which ultimately leads to actuator control: throttle, boost, fuel, ignition, etc.

In a remap, you might:

• Increase the requested load at WOT to unlock more performance.
• Flatten or smooth the curve for better drivability.
• Match it to new hardware (like a bigger turbo) that can deliver more air (Stage 2 and Stage 3 tuning).

3.2: Requested Engine Load Maps:

This is an example for requested engine load map:

Requested Load Maps are typically 2D or 3D:

X-axis: Pedal Position (0–100%)

Y-axis: Engine Speed (RPM)

Z-value: Requested Load (%)

3.3: When tune the Requested Load Map, you control:

1. How responsive the throttle feels
2. How much boost or air mass the engine aims for
3. The starting point for all other torque modeling and control strategies

3.4: Tuning this map wrong can cause:

1. Throttle lag or over-response
2. Fueling/boost mismatches
3. ECU limiting torque elsewhere (torque monitoring/ limp mode)

📍For more information and probable problems feel free to contact us: support@caracaltech.com