lsflame

This is all thanks to KIP SIPMANN

This on a sentra but the same basic theory applies across the board:



The S-AFC intercepts the signal from the airflow meter before it gets to the ECU (Engine Control Unit) and adjusts it to trick the ECU into thinking it's getting more or less air in order to increase or decrease the fuel it adds. It gives you direct control over the amount of fuel going into your engine. Of course, you then have the potential to damage your engine if you try and tune it without an air/fuel meter hooked up.



If you know your car is running rich or lean at certain rev ranges and throttle positions, then you are not getting the full power potential from your engine. After having our stock intake manifold Extrude Honed, Project QG18DE was running a very unfavorable air/fuel ratio. It was so unsafe we didn't even want to dyno the car for fear of causing major damage to the motor under high RPM. Therefore, the need for an air/fuel controller was evident.

The air/fuel ratio is a very common source of confusion to many people. It is the ratio of air to fuel exiting from the engine and a good measure of engine tune. The air/fuel ratio is commonly represented as a single numeral as in 14.7. This actually represents the number of air particles exiting per single fuel molecule (ie.,14.7:1). The 14.7:1 just mentioned is actually what is called stoichiometric, or the ideal air/fuel ratio at which temperatures are controlled and fuel economy is optimized. The air/fuel ratio affects the heat generated during the combustion phase of the engine cycle. Fuel acts as a cooling agent for the cycle. Having a numerically lower air/fuel ratio (less than stoichiometric) is considered to be a RICH condition (ie., richer in the amount of gas exiting) and will result in lower exhaust gas temperatures (EGTs). Conversely, leaning out the mixture by injecting less gasoline causes the overall exhaust gas temperatures to rise. A change from a lean to a rich mixture can cool the exhaust charge by as much as 400 degrees Fahrenheit. The air/fuel ratio can be monitored by an air/fuel gauge or an exhaust gas temperature gauge. An A/F gauge shows the instantaneous mixture while an EGT gauge shows the actual temperatures in the engine to check its condition.

Some common air/fuel ratio misconceptions:

1) Running an extremely rich air/fuel ratio creates more power:
This is a good one for novices who think that you need to consume every last bit of air going into an engine. Actually an engine spits out most of the air it ingests as the ignition cycle for a particular cylinder is far too small and short to effectively utilize the entire air mixture. When high-powered turbo cars or N/A (naturally aspirated) cars run extremely rich mixtures, it is to keep cylinder temperatures down. Frequently cars gain power as they run more optimized air/fuel ratios, typically slightly richer than stoichiometric. In addition, rich mixtures can wear out sensors, waste gas, and clog your catalytic converter. If it were true that more gas always equaled more power, racecars would simply dump fuel directly into the ports instead of worrying about metering. Tuning is the key!

2) Going lean creates an 'instant detonation' condition:
In the case of street engines, this just isn't true. Manufacturers try to keep engines running as lean as possible as often as they can in order to improve emissions, mileage and power. Thus they build in significant safety margins. Detonation isn't actually caused by a lean condition; it is a result of a lean condition. Gasoline actually acts as a suppressor to the ignition event. Leaning out under hard throttle causes temperatures to rise which cause lean mixtures to pre-ignite, but the temperatures are the cause of pre-ignition.

The S-AFC is a fuel computer that adjusts fuel/air ratio by modifying the airflow meter/MAP sensor signal. The S-AFC features a user-definable, eight-point, adjustable fuel curve that can be set in 500-RPM increments. The range of fuel adjustment is +/- 50% at each of the user-defined setting points. On hot-wire vehicles, the Deceleration Air Flow Correction function is capable of curing the erratic idle and stall problems associated with open atmosphere blow-off valves on hot-wire airflow meter systems. The S-AFC is capable of monitoring and replaying the following data channels in Numerical, Analog Meter and Graph displays: Intake Manifold Vacuum/Boost Pressure, Air Flow Capacity, Intake Manifold Pressure, Karmann Frequency, Engine RPM, Throttle Position, and Air Flow Correction %.



"The Apexi S-AFC is a highly versatile fuel computer which allows remapping of the fuel using the airflow /air pressure sensor fitted to most vehicles." - Apexi

Monitor Mode: Allows monitoring of up to 4 channels at one time. Also it allows tracing of AVC-R monitor function.



Setting Mode: Allows user to adjust air/fuel ratio through Hi and Lo Throttle maps. Other features like throttle percentage settings, rpm point settings, and deceleration airflow corrections are adjustable through the setting menu.

Etc. Mode: The etcetera menu is for adjusting the variables that are required for the S-AFC to properly adjust fuel (i.e. # of cylinders, throttle position sensor type, sensor type, etc.)



Monitor Mode: 1,2,3,4 Channels

Up to four data channels can be selected for monitoring:
1. Air Flow
2. Throttle Position
3. Intake Manifold Pressure
4. Engine RPM

Up to four of these parameters can be monitored in three different ways:

Numerical
Analog Meter
Graph Display

If monitored numerically, the user can see a peak hold value for the chosen parameter by pressing the up key.

If monitored in analog meter mode, up to two meters can be displayed at one time. By pressing the up key, the analog meters will hold the peak value.
If under 3 or 4 channel mode, only the first two channels will be displayed. If monitored in graphic display mode, the S-AFC can start "sampling" or memorizing data channels by pressing the up key.

The memorized graph can then be replayed by pressing the right key. Anytime during replay by pressing the right key again, the display can be paused. To review any part of the memorized graph, the user can push the left key during replaying. Anytime during backwards replay, the left key can be pressed to pause the display. If monitoring one channel, then the last 60 seconds can be replayed. If monitoring two channels, then the last 30 seconds can be replayed. If monitoring three channels, then the last 20 seconds can be replayed. If monitoring four channels, then the last 15 seconds can be replayed.

Monitor Mode (2D Trace Mode)

Up to five parameters can be monitored, but only one at a time:
1. Air Flow Usage
2. Intake Manifold Pressure
3. Karmann Frequency
4. Throttle Percentage %
5. Air Flow Correction

The 2D Trace Mode displays one user-selected parameter versus engine RPM. The horizontal scale being engine RPM and the vertical scale being the user-selected parameter. There are three ways to view the 2D Trace. One way is a simple cursor that floats around the screen showing what the user-selected value is. The second way to view the graph is with a 10 point floating trail to show the trend of the user-selected value. The third way is to view with a "Ghost Map" trace. The "Ghost Map" shows wherever the cursor has been and does not clear until the user clears the screen.

lsflame

Setting Mode:

Setting Mode (Hi-Thrtl) (Lo-Thrtl)
The Hi and Lo Throttle setting maps can be adjusted at eight different RPM points that are user adjustable. The range of fuel adjustment is +/- 50% which can be done in 1% increments. During tuning, the Hi Throttle map should be set first, and then the Lo Throttle map. All values between the predetermined RPM points will be interpolated. Only a professional using engine monitoring equipment should be tuning the S-AFC.

Setting Mode (Th-Point)
On this screen there are two values, Lo and Hi. Each value determines whether the Lo-Thrtl or Hi-Thrtl map will be used by the S-AFC for correction. If the Lo value is at 10% and the Hi value is at 50%, then the settings on the Lo-Throtl map will occur between 0 and 10% throttle position and the settings on the Hi-Throtl map will occur between 50 and 100%. If the throttle is between 10 and 50%, then the S-AFC will interrupt between the two values set on the Lo-Throttle and Hi-Throttle maps.



Generally, on turbo vehicles the TH-Point setting can be left close to default or the values can closer together (i.e. Lo-Thrtl: 10 and Hi-Thrtl: 50). On normally aspirated vehicles where airflow and therefore horsepower is strictly dependent on throttle angle, these values can be set further apart (i.e. Lo-Thrtl: 15 and Hi-Thrtl: 80).

Setting Mode (Ne-Point)
This menu allows adjustment of engine RPM points to control fuel. The user can define eight points between 1000 and 9000 rpm in 500-rpm increments. These eight points will appear on the Lo-Thrtl and Hi-Thrtl setting maps.



Setting Mode (Dec.-Air)
Some vehicles equipped with hot-wire airflow meters with forced induction units may experience engine stalling when the throttle is let off. This can be caused by a blow off valve releasing into the atmosphere, lack of a blow off valve, or the use of a very large turbocharger. By using the Deceleration Air Flow Correction function, the S-AFC can prevent the engine from stalling. Please note that this function can ONLY be used on vehicles with hot wire type airflow meters. Please also note that if this value reads **** then this parameter is not functional.

Etc. Mode (Sensor Type)
This menu allows the user to select which type of sensor the S-AFC will be correcting. Look in the instruction booklet between pages 28 and 36 to find out what kind of sensor your vehicle uses. Whatever your sensor type, BOTH the In and Out values should be exactly the same. The sens. Calibration should be left as is. DO NOT CHANGE THE CALBRATION VALUES.

Etc. Mode (Car Select)
This screen allows the user to set the number of cylinders the engine has and what type of throttle position sensor the engine uses. Most Japanese vehicles use an ascending type (arrow pointing to the upper right hand corner) throttle position sensor. If you are unsure of what type of throttle position sensor your vehicle has, you can check the Etc. Mode (sensor check) screen. If your throttle sensor voltage goes from 0-5V when going from closed to open, then your throttle position sensor is an ascending type. If your throttle sensor voltage goes from 5-0V when going from closed to open, then your throttle position sensor is a descending type. If your vehicle does not use a throttle position sensor, then use the "**" selection.

Etc. Mode (Grph Scale)
This mode allows the setting of the maximum and minimum values to be displayed under the Monitor Mode's graph display mode, analog meter mode, and 2D Trace mode. The user can select the following scales:

Etc. Mode (Sensor Check)
This mode will check the voltage of the pressure sensor, air flow meter, or hot wire meter. In-1 is the voltage of the first sensor, while In-2 is the voltage of the second sensor. In-2 will only be used on the Skyline GT-R and will almost never be used in the United States. If your vehicle has a Karmann type sensor, this sensor check screen will not be applicable to your vehicle. This function is to check if all connections have been properly connected after installation. Also if there is improper operation, this screen can be viewed to determine if any connections or sensors are bad.




Etc. Mode (VFD bright)
This mode allows brightness adjustment of the VFD (Vacuum Florescent Display).

Etc. Mode (Initialize)
This mode will restore all data to factory default settings. All previously saved data will be lost. To initialize data, select YES and push the [NEXT] key. Then turn the ignition switch OFF and then ON again. All data will be initialized.
RESULTS

The dyno results proved that the S-AFC corrected the air/fuel ratio and added considerably more power, making it a very useful item. The car went to Streetflight Dyno running pretty lean, above 16.1:1 AFR @ 5900rpm. After the installation, it was operating closer to stoichiometric at approximately 14.1:1 AFR @ 5900rpm on. Again the settings were set somewhat conservatively during our initial testing just to make sure all was working correctly.

Before the S-AFC installation, Project QG18DE use to fall flat on its face at about 5900rpm. This was especially noticeable when pushing into higher rpm. It was as if the parking brake was engaged slightly. After installing the Apexi SAFC, the car now pulls all the way to the rev limiter. We gained 6.23 peak horsepower in the process including substantial gains of a 12-13hp and 11-12 lbs of torque between 5900rpm-6400rpm.

:::NOTE::: We recommend that you have a professional shop install this unit. We had the guys at Streetflight Dyno install our unit and dyno tune the car to make sure all was running well. Settings were set conservatively for testing reasons; there is a lot more room for improvement according to the dyno charts. Because we implore you to have a shop do the installation, this won't be a step-by-step installation article. This is more of an overview and "what to expect" write-up.


http://www.nissanperformancemag.com/...roject_qg18de/

JspecSC3

iTrader: (4)

Wow great write up. I'll definetly add this thread to my favorites folder for future use with my future SAFC2.

duckworth

not sure if you mentioned it, but since it manipulates voltage signals to the map/vam/etc they'll usually die MUCH sooner on you......if you set it and leave it you're usually fine, but i learned the expensive way that if you adjust the a/f ratio often it will destroy the airflow metering sensor........honda maps are pretty tough, but the safc/vafc will destroy one in a month's time if you mess with it.......i knew better but would "street tune" it +/- 1-3% here and there and it cost me.....the time and money to get to a dyno is well worth it if you don't wanna invest in a wideband

setting it and leaving it alone is the best plan

as for installation, anyone who can wire up a radio can wire up an safc/vafc.........just pull the power to the car or a grounded hot wire can eat up an ECU.............i'm SEVERELY colorblind, and i could handle it with apexi's instructions

SPORTcoupe

iTrader: (2)

I didn't feel like reading 2 pages on a gadget I no longer use, but I scanned it over, and it looks like a pretty nice write-up.
Whoever wrote it seems to know what they're talking about, not only with regard to the SAFC, but with tuning in general.

Duckworth: The SAFC can't possibly destroy the MAF unless it's wired up incorrectly.
Reason being: The SAFC (or any such piggyback for that matter) does not modify any voltages going TO the MAF. It read the voltage coming OUT of the MAF, and then produces a lesser/greater voltage(using the supplied 12V) to send to the ECU.

~Alan

EDIT: One more thing I haven't seen mentioned in this write-up or ANY other for that matter...
The MAF produces a 0-5V+ signal.....in actuality it's more like 0.1-4.6V+
Any voltage above 4.6V+ is ignored by the ECU, so if at 5,000 RPM you're flowing enough air to max out the MAF reading (4.6V) and your car is running a bit lean, the SAFC can't help you. Even if you dial +50% on your SAFC, there will not be a change in the AFR because the ECU discards any voltage above max.

duckworth

but it creates a resistance that isn't normally there for the maf/map and i've heard this before and "seemed" to experience that same thing........i used to know the value of that resistance and i'll see if i can dig it up, but it DOES give the map/maf something that it doesn't have under normal circumstances, and an apexi rep was part of a discussion once saying that same thing and how it wasn't covered by their company...........

SPORTcoupe

iTrader: (2)

Hmmmm....that's interesting. I only changed the values in the SAFC-II twice so I can't say much from first hand experience, but it's still weird.
I guess try to stay away from changing the fuel correction curve frequently.

~Alan

Dx3

iTrader: (13)

Awesome write up man

jonny

96sc3

iTrader: (1)

Would changing the lo map affect the car on obd1 or obd2? I mean is it bad to +/- fuel on the lo map? Or just keep the lo map at 0 and only play with the high map.