Engine ECU tuning whats going on.

[Pinkfluffybunnys]

One of the most important and basic engine tuning aspects is dialing in the AFR or air-fuel ratio. This is the proportion of fuel-to-air in the combustion chamber at the time of ignition. Even slight changes in the AFR can have a dramatic effect on power output, drivability and emissions. An AFR of 13:1 means that there is approximately 13 times more oxygen going into the engine than fuel; hence the "thirteen-to-one" ratio. For a given amount of fuel, you need a set amount of air to burn it completely. When the two are present in a ratio that burns both completely, it's called a stoichiometric mixture, or stoich (14.7:1). This is why a stoich mixture is considered "ideal" AFR for gasoline engines.

Unfortunately, 14.7:1 is no magical AFR that will net maximum power. Ideally, an engine should be tuned to have different AFRs under different engine loads and RPM.

Chances are, you've heard the terms "rich" and "lean" before, but do you really know what they mean? It's pretty simple, actually. A higher AFR is a lean mixture, a low AFR a rich mixture.

A rich mixture is one in which there is more fuel present than there is oxygen needed to completely burn the mixture. Slightly rich mixtures leave extra fuel in the chamber and can be good for cooling the intake charge and warding of detonation, but on the downside, rich mixtures can cost us horsepower, decrease mileage, increase harmful emissions, and leave carbon deposits on the valves and combustion chamber. In extremely rich mixtures, the excess fuel can even run past the cylinders and rings to contaminate the oil and possibly damage the cylinder walls and rings.

A lean AFR, on the other hand, is one in which there is more air present than needed to completely burn all the fuel, leaving extra oxygen in the charge. This increases the likelihood of all the fuel being burned and is why mileage increases and emissions are generally lower. On the downside, lean mixtures burn more slowly and at higher temps, which can cause burned valves, detonation and other problems, especially under high load conditions (wide-open throttle).

Tuning the fuel boils down to setting some targets for your AFRs and doing your best to hit those targets. For naturally-aspirated cars, AFR's should usually range from 14.7:1 at idle and very light throttle, 14:1 to 13:1 at part throttle, and around 12.5:1 at wide-open throttle.

The AFR targets for a forced-induction car are a little different. Normally, the off-boost targets will be the same as naturally aspirated engines, but under boost they usually are tuned to run rich, which leaves extra fuel in the chamber for cooling and reduces the chances of detonation. On crappy pump gas (91 octane), most tuners we know tune using conservative AFR targets under boost (around 11:1 to 12:1).

There are different methods for tuning fuel delivery, but all work in one of several ways: increasing the fuel pressure (which increases flow), increasing injector size, modifying the signal to the injector or adding injectors. The first is normally done via a rising-rate fuel pressure regulator, the second is obvious and the third is done electronically by magical boxes that cost a small fortune and the fourth is a no-brainer. We've listed them along with a few terms and parts that are essential to tuning fuel.

Fuel MAP
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This is a grid with engine speed on one side and engine load on the other. The MAP or MAF sensor signal tells us engine load and, based on this and the engine speed, the ECU looks up the two coordinates on the fuel map and injects the correct amount of fuel. Programmable ECUs allow you to change these values and change the AFRs throughout the operating range on the engine.

Oxygen Sensor
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This one's a biggie. This sensor is the device that tells us the AFR. Without it, you can't effectively tune. Mounted in the exhaust stream, it measures the amount of oxygen leaving the combustion chambers and is used by the computer to calculate the AFR. There are two types of O2 sensors: narrow and wideband. Unless you live in the third-world or you like inaccurate data and crappy tunes, get the wideband. It's faster and has a useable AFR range (10:1 to 20:10), while the narrowband works well only around stoich (14:1 to 15:1). If $200 is still too much for the cheapest of ya'll, there's always the DIY wideband O2.

Rising Rate Fuel Pressure Regulator
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Used primarily with low-dollar and smog-legal forced induction kits, this device does nothing under manifold vacuum conditions, but once the engine sees boost, it increases the fuel pressure proportionally with boost pressure. The increased pressure at the fuel injectors means that more fuel gets into the engine. It only works with return-type fuel systems and since it does not change the signal to the injector, you can't fine-tune it.

Injector Signal Modifiers/Generators
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For simplicity, we've grouped together all the electronic devices that change or replace the signal to the fuel injectors; including ECUs, AFCs, piggybacks, re-flashes, etc. What these devices do is control how much fuel is delivered to the engine. They typically have their own displays or link to a laptop computer to allow the user to add or subtract fuel according to the wideband in order to hit their AFR targets in all the different "zones" on the fuel map. The fancier ones have features that allow it to communicate with the oxygen sensor and self-tune the AFR for all the different engine loads and speed all by themselves--while you drive.

Extra Injector(s)
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Just what it sounds like. Mounted somewhere in the intake tract (usually near the throttle body), the extra injectors are controlled by an extra computer. A downside to these units is that fuel can only be added, not subtracted from the base map.

MAP/MAF Sensor
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Most fuel-injected cars have either one of these sensors. This is the signal that will tell you the engine load. Learning to interpret this signal is the key to getting a good tune. Depending on the load, you need to vary the AFR. The MAP (manifold-absolute-pressure) sensor is mounted on the intake manifold and tells the computer how much pressure or vacuum is in the manifold. Based on engine speed and load (MAP), the total airflow can be calculated. MAF (mass-air-flow) sensors measure airflow directly.

Spark Tuning
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Unfortunately for the backyard tuner, developing a good spark map isn't as straightforward as tuning the fuel with a wideband oxygen sensor. Ideally, a spark map should be developed on a chassis-loading dyno (Mustang). The car is run on the dyno and for every RPM and load bin (the spot on the spark map), the ignition timing is advanced until torque starts to drop off. The point right before the torque drops off is called MBT or mean best torque.

There are a couple of problems with this method. One is the cost of renting a dyno for hours on end. It could easily cost a fortune to get it nailed. But the biggest problem with this method is that many engines (especially high-compression and forced-induction) will encounter knock before reaching MBT. Most engines will ping before reaching MBT.


Because of this, we must keep an ear out for knock while tuning. While knock can be heard, it's much safer to rely on a knock sensor to serve this duty. It's safest to make only changes where needed to the spark map. Typically, the low-load ignition timing that the engine uses stock is best. It's really only under high load and with higher-compression pistons, etc. that other areas in the spark map might need to have some ignition advance removed.

When tuning ignition timing with a knock sensor, you simply reduce the timing advance under those conditions that you encounter knock. There are numerous to control ignition advance. We've listed a few ways and some other terms that will help you.

IAT Sensor
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The intake air temperature sensor tells us the how hot the air is as it enters the engine. The higher the temp, the higher the chances of knock. If intake temps can be lowered, more ignition-timing advance can be added, which adds power (unless you've hit MBT, which is unlikely under a high load). This ability to add advance when temps are lowered are part of the reason why cold-air intakes and intercoolers can add power.

Detonation
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Detonation, or knock, is when the air/fuel mixture ignites before the cylinder reaches maximum pressure. The result is a supersonic and out of control explosion in the chamber that puts stress on the engine that it wasn't designed for. Low-octane fuel, high compression ratios, advanced ignition timing, high intake temps, and a number of other things can cause detonation. Detonation breaks pistons and bends rods.

Preignition
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This is when the mixture ignites before the spark plug fires. It is caused when isolated spots in the combustion chamber glow red-hot and ignite the mixture before it's supposed to. These hotspots can be caused by carbon build up, poor design, or other factors. Preignition isn't the same as detonation or knock. Anyone who's been in a junker that keeps running after it's been shut off knows what preignition is.

Knock Sensor
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A knock sensor is a device that measures engine noise and sends a signal to the computer when there is detonation. Most sensors have some "background" noise in their signals, but real knock events are easily distinguished because they are so violent and register big values when it happens.




Thanks Import tuner

[rat]

thx for the info, has helped me understand a bit

[Draco]

Here is a link to a car dyna program.....maybe someone can use it...desktopdyna....

http://carprogrammer.com/Z28/PCM/Tools/

[Riekert]

Here is a link to a car dyna program.....maybe someone can use it...desktopdyna....

http://carprogrammer.com/Z28/PCM/Tools/

thats a awesome little program man!

[Pinkfluffybunnys]

kick ass program