This article is a note after learning about AF/Trim and some related knowledge. As a non-vehicle engineering related person, some of the article content may not be correct and is for reference only.
Many times we may replace our car with an air intake kit that is different from the original air intake kit for performance improvement or the need to show off. For example, I replaced my FK7 with an Injen EVOLUTION some time ago. Cold Air Intake System – The intake system of the EVO1500 is the same intake system as the one in this video. It is an intake system with a bellows that uses a dry filter element.
But after replacing the air intake assembly, I have been wondering whether this new air intake assembly is really compatible with the original car, how do I know it is working properly?
Datalog
Since I happened to have the Hondata program in hand, soon after installing the air intake, I plugged in the Hondata and drove outside to record the data stream for a period of time and took it home for analysis.
Although we can see on the official website that Injen’s description of this air intake is “Dyno Proven gains of up to 13 hp and 12 lb-ft. of torque” and “Designed to work with the stock calibration”, but it is measured with Hondata (The corresponding program is the original version of “Canada 2018 MT – Civic Turbo MT 2017, +6 psi high octane”).
If you don’t check the “Injen CAI/SRI” option in the Mod, KC will be around 68% all the year round, and there will be 6-7 Knocks after driving for 10 minutes. At this time, the car will feel more fleshy when driving.
If the “Injen CAI/SRI” option in the Mod is checked, KC will recover to about 56%, and Knock is not easy to appear. Compared with unchecked, the 0-100km/h acceleration score can be 0.5 faster s or so.
So from this point of view, even if you use this air intake with bellows, using “Injen CAI/SRI” is still a better choice than the original program. If you use this air intake, please don’t blindly believe what some people say There is no need to adjust the program or the like, otherwise your car may have been working under a high KC.
KC and Knock
In the above, I used a word called KC. The full name is Knock Control. The Chinese translation is Knock Index. It is explained as follows in the articleWhat is Knock Count and Knock Control (defined) :
“Knock Control” = This parameter is the ECU’s determination of fuel quality. Movement here indicates the knock sensor hears what it thinks is knock activity, and reports to the ECU to apply a steeper ignition retard to avoid continued knock activity. This value is dynamic , and WILL move from time to time.
On Civic Si models, there doesn’t seem to be a forced rise at play at WOT like the non-Si 1.5T ECU’s (which naturally rise above 5,200-5,400rpm regardless of sensor input). Movement that goes up and up and up and never comes down is more concerned than movement alone. Knock control can typically be manipulated down by driving the car in a higher gear at lower engine speeds and targeting atmospheric pressure on the MAP sensor reading.
In another post ( Has anyone used the Hondata +6 PSI tune on CVT with Regular Fuel ), some netizens said
I really hate when people claim these cars don’t knock. The computer will do what it can to prevent it based on estimate algorithms combined with knock sensor activity but it surely isn’t ideal to have any knock control higher than the 49% or 54% depending on which tuning software your running. Period. Even stock.
From the above posts, we can conclude the following conclusions:
- The level of Knock Control mainly depends on: oil quality, whether WOT (full throttle, which can be understood as full throttle), some sensor data, and data obtained through the knock sensor (for example, the knock sensor sees some Knock , it will raise this value)
- The original program of the 1.5T non-Si Civic will increase the value of Knock Control (that is, Artificial Knock) at 5000-5400rpm and above
- Knock Control will become higher after intense driving
- Ideally the value of KC should be 54% (or 0.54)
In the above, we saw that if the “Injen CAI/SRI” option is not checked, the KC will be high, but after it is checked, the KC will come down. Here we need to understand what this option has changed.
AFR and Closed Loop
After consulting the information, we can know that “Injen CAI/SRI” mainly changed AFM, so what is AFM, and why its modification will affect KC, here we need to involve two preliminary concepts, which are called : Closed Loop (closed loop control) and AFR (air-fuel ratio).
Regarding what closed-loop control is, I intend to directly copy the explanation in the article P0171/P0174 Fuel System Too Lean (System too lean) Fault Diagnosis Process :
Each bank of the engine has two oxygen sensors. The front oxygen sensor is located downstream of the exhaust manifold and upstream of the three-way catalytic converter, and is responsible for feeding back the oxygen content data in the exhaust to the computer. The rear oxygen sensor is located downstream of the three-way catalytic converter, and its data does not affect the behavior of the engine, and is only used to monitor the performance of the three-way catalytic converter. The oxygen sensor data will be used to detect the combustion status. If the oxygen sensor data shows that the system is too lean (lean condition), the computer will command the injector to inject more fuel (rich command); otherwise (rich condition) will inject less fuel (lean command).
When the engine is just started, it will be in open loop control, because the oxygen sensor cannot read the data when the temperature is not enough. After both the oxygen sensor and the water temperature reach the operating temperature, the system turns into closed-loop control. In some special cases, such as when the engine is just started (even if it has reached the operating temperature), the throttle is wide open (Wide Open Throttle), the computer will force open-loop control.
As for the air-fuel ratio, the introduction on Wiki is:
Air-fuel ratio (AFR for short) refers to the mass ratio of air to fuel in an internal combustion engine. If it is exactly equal to the stoichiometric ratio that allows complete combustion of the fuel, it is called the stoichiometric air-fuel ratio. The air-fuel ratio is a very important parameter for reducing emissions and improving the performance of internal combustion engines.
That is, the mass ratio of air to fuel at the time of combustion. Gasoline has a stoichiometric air-fuel ratio of about 14.7 and diesel about 14.3.
Here we will come to a conclusion that the engine’s control of fuel injection and combustion under non-WOT (full throttle) conditions requires multiple sensors to monitor. In an ideal state, the engine needs to control the intake and fuel injection. (to achieve the optimal air-fuel ratio of 14.7), but to know the air-fuel ratio we need to know two data – the fuel injection volume and the intake air volume. The fuel injection volume is easy to calculate. It is sprayed, and the calculation of the intake air volume requires the intake air flow sensor.
The intake air flow sensor is called MAF——Mass Air Flow sensor. It is usually inserted on the pipeline of the intake assembly. I found a web map of the tenth generation Civic. The one in the white circle is MAF.
For non-Si Civics (such as our ordinary tenth-generation Civic), the data read by MAF is a voltage between 0 and 5V (not the actual flow rate in g/s ), in order for the engine to understand There will be an AFM setting according to the actual flow rate of the intake air under the corresponding voltage. The original AFM curve is calibrated according to the original intake bellows. This calibration is a table, which looks like this:
But after modifying the air intake, for example, in my scene, the actual air intake will be much larger than the original one. If you continue to inquire according to the original table, the computer will get a higher than the actual one according to the curve under the same voltage. The value of the air intake is low (for example, the voltage is 3V, the computer checks the table and thinks it is 40g/s of intake air, and then injects fuel according to this amount, but in fact 50g/s of air has been sucked in), at this time The engine will determine the fuel injection amount based on the wrong intake air volume. The actual effect is that the AFR (air-fuel ratio) is wrong, and the actual intake air is more, resulting in higher AF (lower fuel injection concentration), which leads to easy Knock and KC are higher.
How does the computer know that the AFR is wrong? We mentioned above that under most working conditions, the ECU of the car operates under closed-loop control. When the exhaust end of the engine has not reached the three-way catalysis, there is a front oxygen sensor. This sensor will know the residual combustion Oxygen content, if it is less than a certain value, then there is too much fuel injection, if it is greater than a certain value, then it must be that there is less fuel injection. In the above working condition, the front oxygen sensor found that there is more in the exhaust gas. Soon the computer knew that it had injected too much oil. In order to ensure that the mixture is fully burned, the engine needs to be corrected with S Trim and L Trim.
This is what Brother Yoyo said in a certain program: If the program does not make corrections after you change the air intake, the computer will feel very strange.
Fuel Trim
In order for readers to understand the working principle of Trim more intuitively, here is a screenshot of the data I recorded:
It can be seen that at the selected point:
- AF is 15.81:1
- AF CMD is 14.97:1
- S Trim is 4%
- L Trim is 0%
Here we can get the following information: Under this working condition, the engine expects the air-fuel ratio of in-cylinder combustion to be 14.97:1, but the actual air-fuel ratio calculated according to the front oxygen sensor is 15.81:1. It is thinner. In line with the principle of adding noodles when there is too much water, and adding water when there is too much noodles, the engine is given a 4% S Trim (short-term fuel trim), allowing the engine to inject more oil to alleviate this situation.
On Hondata’s website we can see:
Normally short term fuel trim should be within the range of -10% to +10%,
Normally the long term fuel trim should range from -5% to +5%.
Generally speaking, the short-term fuel correction is more reasonable between plus and minus 10%, and the long-term fuel correction is more reasonable between plus and minus 5%, but this value is not necessarily as close to 0 as possible. In the post My 0 knock count, constant 54 In the % knock control cal experience , we can see that when the owner is in a country that is very hot all year round, the S Trim is the most stable between -5% and -15%. If you want to deliberately adjust it to close to 0, it will easily cause explosion shock.
AFM
After having the above knowledge, we need to judge whether our AFM is correct or not. Here is a little trick for judging. After we record data such as 20 minutes and import it into Hondata, we can find the XY Graph in the Advanced Graphs above. .
Then select AFM.v for the X axis, select S Trim for the Y axis, and only tick the Closed Loop operating condition data, so that we can see the fuel correction under different AFM.v conditions in the Log data.
If you understand the above, the guiding principle here is clear. Since AFM is a curve, if your actual air intake in a certain area is inconsistent with AFM, it will inevitably cause the average line under the corresponding area to seriously deviate from the center. For example, if there is a section of your curve that is particularly low (indicating that a large number of high short-term corrections have occurred), then you need to find the corresponding range of voltage values for that section, and increase the value in the corresponding interval in the AFM. ,vice versa.
The above, as a little fun in the era of internal combustion engines, I hope to give some help and reference to readers who read here~
This article is transferred from https://nova.moe/honda-afm-intake/
This site is only for collection, and the copyright belongs to the original author.