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Old 07-17-2002, 05:53 PM   #1
Scooby Newbie
Member#: 707
Join Date: Jan 2000
Location: cottage grove, mn, usa
99 Legacy GT
Quick silver

Question SAFC questions

after doing much research i am more confused then when i started, so now i post these questions to all of you into the legacy forum to get information from those that know it.

i am not looking for opinions, there are lots of peole in this forum that are very knowledgable, and also many that have lots of experience, and lots with both. so i am looking for personal experience, and facts.

maybe if we get some good info on here we can make a sticky out of it...

Questions to be answered.

1. How do MAF and MAP cars differ when it comes to A/F ratios? is one type rich the other lean?

2. Does the SAFC work with MAF? i have just read that these cars(like my 99) are able to continue to adjust to different airflow sufficiently to regulate fuel without the SAFC.

3. How do you tune the SAFC with a A/F gauge? some people say balance it, others say a little lean, others a little rich. what is correct? We need some specific directions on tunning. ex. how do you put a load on your car at 4000rpm to see if it is lean or rich, and at every other rpm you are going to adjust.

4. do these settings need to be change often? cold vs warm, when you get a new mod? ex if i get shop to setup the SAFC now, then in the winter, will it still be working well, or after i get headers?

5. What settings have worked for you, and what car with what mods are you running?

i hope this all makes sense, and hope we get some real good info.

let my start with a link for some of you to do some reading about SAFC and MAP cars

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Old 07-18-2002, 01:54 PM   #2
MY99 2.5GT
Scooby Specialist
Member#: 5030
Join Date: Mar 2001
Chapter/Region: MAIC
Location: Martinsburg, WV, USA
1999 Legacy 2.5GT
12 Legacy GT 13 Armada



As you probably already know MAF or MAP sensors don't really determine whether the car is normally rich or lean. This is determined by the preset maps stored in the ecu. It is known that 2000+ models characteristicly run rich. While the 98-99s characteristically run lean. I have heard the reason they run rich is because of a less sensative knock sensor. From my understanding MAF sensors are a little more accurate then speed density systems with MAP sensors.

Yes the SAFC will absolutely work with a MAF sensor and will also work with a MAP sensor.

" i have just read that these cars(like my 99) are able to continue to adjust to different airflow sufficiently to regulate fuel without the SAFC."

The above statement is absolutely correct. As said above we are not worried about the sensors ability to determine differences in airflow what we are worried about are those darn fuel maps in the ECU that cause our engines to run too rich or too lean for optimal performance. Every aspect of the ECU is set up to provide you with the best fuel economy and the most protection against failure for your engine in its stock form. However when you mod the car with performance parts that cause more air to enter and exit the engine you will also want to tune the fuel curve very basically based on the above premise that really rich = power loss and really lean = engine damage.

I'll let someone else share their expertise for question 3.

I like question number 4 because it partially addresses an aspect of tuning this unit that not many people think about. Yes you are tuning air fuel ratios but you need to tune based upon what reactions you get from the car. In order to precisely tune the safc you need an air fuel metering device that will measure and log numbers not just a gauge with lights bouncing back and forth. You will also need to keep a very close eye on what your exhaust temperatures are doing. I have heard a 14:1 mixture is the magic number. You now need to find out what the magic exhaust temperature is and tune to keep both fuel mixture and exhaust temps as close to those magic numbers.

By far the best way to tune is on the dyno. That way you can see exactly how the modifications you are making to the mixture affect power at the wheels.

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Old 07-18-2002, 02:39 PM   #3
Scooby Newbie
Member#: 707
Join Date: Jan 2000
Location: cottage grove, mn, usa
99 Legacy GT
Quick silver


good information brad. here is some more good stuff i found while searching the tons of info online. i like this because it is specific based on personal information but is prettys specific.

kevin drives or at least drove a 1989 XT6 FWD when he wrote this

anyone else have some good information to share?

Originally posted by Kevin Thomas
This is why we need some type of FAQ section somewhere on tuning our Subarus. These questions should've been answered a long time ago. I never knew at what voltage point was considered stoic until I read this post. Here is some information that may help that I 'think' is correct from reading (and tuning) over and over again here:
[list][*]Try to connect to the O2 sensor closest to your header/exhaust manifold. This O2 sensor will give you a more accurate reading since it's closer to the actual exhaust ports in your cylinder head.[*]In voltage, I personally feel you should shoot between .80-.85. Turbocharged .89-.91. EGT's usually will run close to stock if you try and shoot for air/fuel ratio voltage in this range, generally.[*].55 voltage is the point where your air/fuel ratio meters will change from lean to rich since in voltage there is no transition stage. [*]Your air/fuel mixture is supposed to fluctuate back and forth from lean to rich over and over again while idle. If the O2 voltage is stabilized at the middle of (0.45-0.55) or if the O2 sensor fluctuates very slowly (crossing .55 volts less than 5 times in 10 seconds), the O2 sensor may be faulty. *Haynes manual and personal experience*[*]If you do run into lean (below .55) conditions during WOT runs, do the following:
  1. Don't go WOT! It seems obvious but it has to be said.
  2. Richen your air/fuel mixture until you get to .80 or slightly above.
  3. Purchase higher octane fuel. This helps prevent detonation just in case you have to run WOT (Merging into traffic).
  4. If you have lots of N/A modifications and you've gained 50hp or more, purchase colder (by 1 degree) spark plugs.[/list=A]
  5. If all else fails, purchase a new O2 sensor. You will be surprised at how often O2 sensors fail and is the culprit of your problems.

I don't know what to say for those with non-voltage reading air/fuel ratio meters (those than just read rich or lean). I need to know how rich or lean something is. Your air/fuel ratio meter can read rich when you are actually running in the .55-.60 range, which is really, really borderline lean. In this case you'd have to rely on your EGT's but that's another discussion. There is a lot more info about O2 sensor tuning or what not but I'm no expert. Just keep asking around for more info.

My suggestion for a good voltage O2 sensor is the Jumptronix Air/Fuel Ratio meter (www.jumptronix.com). It reads in voltage and mounts on your steering wheel column. Really clear day or night and is easy to read while driving. Also, you get an volt meter reading too, simply by hitting a switch/lever in back of the unit. It's been very useful for me and I plan on getting one (or a unit like it) in all of my future vehicles. Take Care!
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Old 07-18-2002, 02:47 PM   #4
Scooby Guru
Member#: 15543
Join Date: Feb 2002
Location: san francisco, ca
90BJ Legacy LS ABS
AWD 946 Rio Red Jpn built


Maybe its just me but really Id say that tuning an A/F guage to air fuel mixture is probably a waste of time. Of course it could be a good start but I wouldnt leave it that way. The price of an A/F mixture modifier should be considered to include tuning. Its not wise to think "I can spend 300 and get x hp from this apexi." More like 300 + some dyno time.

Im planning on spending the money to put the car on the dyno so that it will log HP/TQ and air fuel mixture. Then Ill tune it to flatten that third reading out and retest, do it again and so on.

Just to get the car running decently I will attach mine, then tune it as you say so that the WOT fuel mix is just slightly rich. Dont try tuning the normal throttle stuff, your ECU will just compensate. Let the Air flow meter do its job at low throttle, getting good gas mileage. Focus the attention at 90%+ throttle.
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