Knock and Knock Retard (KR) – Knock is an event which occurs when a sudden and violent rise in cylinder pressure tries to make the piston travel backwards. This event can range from almost harmless to “my engine blew up”. There are many causes. The mixture could be too lean. The spark could be too far advanced. The engine temperature could be too high. The load on the vehicle could be too high. Many, many reasons. Diagnosing knock is no trivial task. In the mean time, the car has a built-in failsafe to protect you from this. It’s called KR and it is a computer driven correction to your spark tables that removes timing (lowers the degrees) until the knock goes away. The knock itself is detected by a small piezoelectric microphone that analyzes the engine’s vibration. When it detects a knock pattern, it starts to trim timing until the knock goes away and then it slowly adds it back again, keeping the car in the safest condition possible, given the default values.
O2 – The oxygen level in your exhaust pipe is monitored by the O2 sensors and by the computer. It is a voltage divider that returns a low or high voltage indicating an excess or an absence of oxygen respectively. This tells the computer how to adjust the AFR described above. It is a closed loop system. In other words, the computer attempts to guess a good value for car key maker the mixture based on the MAF (below) and tries it out. The O2 sensors figure out whether the chosen mix was rich or lean based on oxygen content and FEED BACK the data to the computer, which adjusts the future AFR to compensate and so on and so forth.
Fuel Trim – Fuel Trim comes in 2 flavours, long term and short term. One is long lasting, the other is fast acting, kind of like allergy pills. The fuel trim is a numerical representation of how much the computer needs to compensate for a given fuel mixture. If the mixture is really rich for example, you’ll see a big negative number like -15. This means “Take away 15 units of gas... there’s too damn much!”. First this will show up in the short term trim and then you’ll see the long term trim lag behind and catch up, provided the short term trim stays where it is. AutoCom Thus the long term trim “learns” from the short term one and the computer has a limited memory for this. The trims are in place to make day to day adjustments to the fuel tables because of things like the properties of the air (winter vs summer for example). It’s also noteworthy that the O2 sensors play a part scanner for car in setting the trims.
MAF (Mass Air Flow) – The intake plumbing in your car (where the airbox is) contains a MAF sensor, which detects the MASS of air entering the car at any time. This is extremely important because it tells the car how much gas to inject. It’s usually measured in hertz (Hz) and is non-linear… and confusing. You have to find a conversion table to convert these values into something meaningful like grams/sec.
MAP (Manifold Absolute Pressure) – A “somewhat” redundant sensor, this is still quite important and it measures the absolute (above 0) pressure of air in the manifold, where the air gets split up into each cylinder. It is analogous to engine load, since more pressure usually means higher throttle and more acceleration.
PE (Power Enrichment) Mode – Remember AFR? Keeping it at stoich is great for fuel economy but when you floor it, this ratio is no good anymore. Why? First, the engine is under high load and this makes it hot. Hot engines are not good. They cause pre-ignition of the fuel and knock. To counter this, you need a coolant. Excess gas is actually a decent coolant because it cannot burn (for lack of oxygen) so it’s just extra liquid soaking up heat in the chamber, keeping the temps down. Chemists will tell you that anything other than stoich produces less power of combustion. This is true when you look at both air and fuel as changing quantities. However in an engine, you don’t have less air and more fuel. You have the SAME air and more Famous OBD2 OBDii Brand Launch fuel. A little extra gas doesn’t lose you anything and in fact you get more power up until a point. Tweaking the ratio used in PE mode is key when you modify anything related to the engine or fuel system. The other thing is that flooring the car makes the RPMs shoot up. High engine speeds mean everything has to occur much faster. The atomization of fuel through the fuel injectors is somewhat inefficient and proper atomization becomes more of an issue when there’s less time for it to occur. Adding more gas in PE mode ensures an excess of gas droplet surface area exposed to the air so more of it will get ignited. This compensates for the inefficiency of running under load.
AE (Acceleration Enrichment) – This is a table that commands extra fuel instantly when you press the accelerator. The idea is to rapidly anticipate a greater demand for gas. When you hit the accelerator quickly (as opposed to slowly) it changes the airflow into the engine very suddenly. This could cause a brief lean condition, which could damage the engine. The AE table takes sensor data from the accelerator to figure out how fast you pressed it (not how much) and to add extra gas right away for a short time, to meet up with the sudden burst of air about to enter the cylinders.
Injector Pulse Width – Fuel injectors are on/off devices. They have a constant pressure driving them and open for a variable amount of time during each pulse, depending on demand. This is also known as the duty cycle of the injector. When you start modding your car you may increase the capacity of the engine to take in air. Adding a supercharger will do this for example. The problem is that the duty cycle of an injector can only go to 100%, which means it’s always on (called “running static”) and never turns off during each pulse. Beyond that you don’t get any more gas, your engine leans out and you have an expensive explosion. You need to keep this in mind because some mods require you to get bigger injectors (which can flow more gas) and a fuel pressure regulator, which will supply greater pressure to those larger injectors so that their flow reaches maximum potential.
VE (Volumetric Efficiency) – This is tricky to explain. It’s another 2 dimensional table consisting of manifold pressure and RPM, similar to the spark tables. This time though, the cell values are not angles. They are efficiencies represented as decimals (1 being 100% efficiency). Imagine a cylinder cut in half. As the piston goes from top to bottom, the volume of air it sweeps out is the theoretical capacity of the cylinder. For most engines, most of the time, you don’t get all of the air that space could hold because the engine has to suck the air in and that creates a bit of a vacuum. Thus the air that enters the cylinder represents a slightly smaller volume than the geometry would suggest. This produces a volumetric efficiency of less than 1. Sometimes however, when you have a tuned induction/exhaust system or a forced induction system (supercharger, etc.), more air will enter the cylinder than it should normally hold and you get a VE greater than 1. This table is used as a sanity check, especially when the car is under high load, so that the computer knows how to adjust fuel and spark values to respond to anticipated cylinder pressures.
Open/Closed Loop – As stated earlier, the car is usually running at stoich due to a feedback loop involving the O2 sensors. This is called closed loop mode. Because of how fast things occur when you floor the engine, it’s hard to maintain closed loop so the computer shuts that off and relies more on lookup tables and the knock sensors. This is called open loop. Open loop is also triggered when PE mode is enabled. When you tune your car you can choose when this occurs, usually as a function of throttle response (ie. The pedal’s position is measured as a % of being fully floored)
Torque Management – I hate this garbage. It’s a set of computer algorithms that detect when you’ve overstressed the drivetrain. It’s meant mostly to protect the transmission... which is good, don’t get me wrong. It’s one of those things that promotes durability of the vehicle, which is to say you can usually tone it down or remove it without causing damage, in the short term. Before messing with this Xhorse I highly recommend checking all of the specifications of your hardware to be sure that your car can handle it. The effects of torque management are to augment the fuel and spark settings, to intentionally rob the vehicle of power, when it thinks there’s too much.
Limiters – The car places limits on how fast you can go and how high you can rev (among other things). As long as you don’t intend to abuse these for illegal purposes, you can remove them for use on the track. The limiters turn off the fuel injectors as a way of shutting down the engine at certain speeds and RPMs. If you disable that feature, the car will go as fast as it can and rev to whatever speed you set it to. WARNING: Setting the RPM limit too high will cause valve float (where the valves don’t have time to close) and harmonic mechanical strain that will cause performance to drop and possibly wreck your car.
Fan On Temps – Your car’s radiator is equipped with fans that remove heat from your engine coolant. You need this or your rad will blow and your engine will seize. Setting the temperature thresholds to turn the fans on and off obd2 code reader will help you regulate the coolant temperature at different times of the year or keep the temps lower auto accessory for racing purposes. However, the thermostat cannot be controlled by tuning and it is what controls the actual fluid flow so ultimately you can’t hope to lower coolant temps very much unless you install a lower temperature thermostat. This will allow coolant flow to the rad at a lower temp than stock.
Transmission Shift Time – This is the commanded time it takes to shift an automatic transmission from one gear to another. It’s just a command though and the transmission itself will try to obey but might not be able to if there’s too much load on the car. See below for an explanation.
Transmission Shift Pressure – If your car has an automatic transmission, the shifts take place by moving hydraulic fluid around through different channels, causing bands, plates and clutches to engage/disengage. The fluid pressure controls how aggressive these events are. Upping the pressure can prevent your transmission from slipping when engine torque is high. This becomes increasingly desirable as you add more power to your car or start reducing shift time, as it allows the tranny to “bite” into the next gear better.
Transmission Slip – Whether you have an auto or a manual transmission, there are friction components that make shifts occur. These are called clutches (bands and clutches in autos). When you try to shift gears, the clutches press against each other at different speeds and try to reach the same speed through frictional braking. If the clutches are not rated for the power of the car or they are worn, they will slip. All clutches slip actually but we’re talking excessive slip. Excessive slip causes slow, whining shifts and generates heat and debris in the transmission oil. This wears out the transmission, makes the car run terribly and could lead to failure. Make sure you have the right transmission components for the job.
EGR (Exhaust Gas Recirculation) – This is a part of your emissions system. It reduces NOX production AutoCom by lowering cylinder temperatures necessary to produce these nitrogen species. It works by injecting exhaust back into the engine again. Heh.. hehe… hehehe. I turn it off at the track because I don’t want exhaust going back into my engine again. Honestly, it does not have a big impact on performance because it shuts itself off automatically when you floor it. However I still believe that response time is everything so I turn it off.
Torque Converter – This resembles a turbine inside and works by transferring power from the engine to the transmission by pumping a viscous fluid from one set of blades to a nearby set of blades. The viscosity of the fluid transfers shear force between the blades and makes the output side move in response to the input torque. In this way, you get torque transfer without any physical contact. That’s why autos are so smooth feeling. Most contain a clutch though that can lock to produce a mechanical coupling.
Torque Converter Clutch – In automatics, this thing removes the fluid coupling of an auto and locks the input and output together, essentially making it behave like a manual transmission. It only happens when you’re cruising at a stable speed and it improves fuel economy. It’s important to know about because when you’re cruising (and it’s locked) and you suddenly floor it, the computer has to tell the clutch to unlock because the clutch isn’t made to handle that much stress. This process is slow and may take a second. During that time the car bogs and then kicks in all at once. If you try to pass someone on the highway you’ll know what I mean. For performance applications it’s best to tune the torque converter to be off the whole time. This eliminates any bogging effect but your mileage will decrease so change the tables again when you hit the road home. If you feel like risking damage to your car you can intelligently enable it during full throttle, at the end of a gear, to extend the range of that gear for some extra torque at the top end but I wouldn’t recommend it.
WOT – Wide Open Throttle. This means the pedal is 100% down. Some special things happen in a car’s computer when this is detected.
PCM – Powertrain Control Module. It has some other names too but it’s basically a chunky, heavy, dirty, metal box containing a computer processor from the 80s. It’s crude but very reliable. It contains some limited memory and runs 512 Kb files that contain the entire operating system needed to operate the car as well as a user block that contains all of the tables and settings that can be modified. It generates all your trouble codes, interfaces with all your powertrain sensors and can turn into a paperweight if you don’t know what you’re doing when you try to program it. The OBDII port is normally somewhere under the steering column on the driver’s side. This port allows read and write functionality between the PCM and a computer (Serial/USB/Bluetooth), provided you buy the appropriate interface module.
Well, we’ve certainly covered a lot of material. Stay tuned for more and remember, I can’t guarantee 100% accuracy of the above material and I’m not responsible for anything you do, whether it was your own idea or influenced by this article. Be careful and have fun with your ride :)
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