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Old 06-25-2001, 12:47 PM   #1
skywalker
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Join Date: Jul 2000
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Question Air/Fuel Ratio

I installed a Air/Fuel Ratio Guage in this weekend and I am trying figure out what are the correct settings on my setup.

[bold]Other items of interest.[/bold]
99 RS (both O2 sensors range from (0.0v - 1.0v)
Apex-i S-AFC
Apex-i S-ITC (set to all 0's currently, trying to figure out AFC)
EGT
Amsoil Drop in Filter
Using the 2nd O2 sensor for Air/Fuel Guage

[bold]What I have things set at right now.[/bold]
AFC is set as:
RPMs (for low throttle, below 35%)
1000, 2000, 3000, 3500, 4000, 4500, 5000, 5500, 6000
-1% -3% -5% -5% -5% -3% 0% 0% 0%

It seems to be running well but my Air/Fuel Ratio Guage is always running into the rich area on the 2nd O2 sensor. The number that is being displayed on the AFC when idle is ranging from 0.5 -> 0.7. When I go to WOT it is getting up around 0.875. At cruising speed on the highway in 5th at about 3200 RPM's it is at about 0.500.

Are these sounding good, bad? Anyone with a lot of experience in this? What are some numbers I should be seeing at different points? Should I be using the 1st O2 sensor?
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Old 06-25-2001, 12:52 PM   #2
jeffg
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Just to point out and idea. I would use the first O2 sensor, not the second. The second O2 sensor will be behind the cat, and therefore inaccurate. The cat is changing the AF ratio and removing fuel. If both of your O2 sensors are truely 0-1V, then use the front. I have heard stories of people using an AFC to remove a lot more fuel than you are and still running rich. Make sure the guage is accurate, then start tuning.
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Old 06-25-2001, 12:54 PM   #3
Santo Domingo 2.5 RS
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you should use thge first O2 sensor
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Old 06-25-2001, 04:35 PM   #4
skywalker
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Question

Well i tried it on the first O2 sensor and it seemed like I am having the same issue as everyone else. My car is running way to rich. I really don't want to lean it out to much because I really don't want to damage the engine. But the reading is saying it is running to rich.

Also isn't the first O2 sensor in back of the first Cat? The second sensor is in back of both of them so really niether will give you a real good reading.

Just a quick question what numbers are most RS's trying to get for a reading? 0.875 NA and what about Turbo?
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Old 06-25-2001, 04:57 PM   #5
jeffg
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The frist O2 sensor is mounted into the first Cat housing, but in front of the actual Cat material plate. This will be a much more accurate reading of your true AF ratio. The EJ25 runs very rich from what I hear. This may be an extreme case, but I have heard of some cars needing as much as 47% fuel cut to reach near 14.7:1 ratios.

Please do not run out and do this. Fuel tuning is an art and needs to be carefully monitored in order to protect the engine.

Jeff
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Old 06-25-2001, 05:52 PM   #6
skywalker
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Thumbs up

jeffg,

Well that is why I am posting here first. I also did a search on yahoo and on this message board to see what other people are running.

I will slowly work my way to some point and see what happens along the way. I try to stay away from major changes right off.

Thanks for the info, I will change the sensors tonight and see what happens.
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Old 06-26-2001, 12:18 AM   #7
Captain Ding
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I certainly can't claim to be a tuner or anything, but I believe anything above .85V means you are running rich. Also, it looks like you posted your low throttle settings, but are concerned about WOT air/fuel mixture. Did I just misread it? What's your hi-throt setting? BTW - I have a 99 RS and have to RICHEN it by as much as +18% at 5500 RPM hi-throt. I'm right around .8V (+/- .01V) from 3000 - redline reading from the 2nd O2.
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Old 06-26-2001, 02:59 AM   #8
skywalker
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Captain Ding,

That sounds like to me you might be running it to rich. I could be totally wrong. I am going to switch O2 sensors and go with the first one.

For high throttle above 70% I have it set to nothing right now. For me it seems to be running at a consistent 0.875 at WOT or near that from 3000 RPM'S and up on the 2nd O2 sensor. If I am getting that kind of reading on the 2nd O2 sensors I would lean out the mixture. Well that si what I plan on doing.

Right now I am having problems tellign what the readings are at idle, they fluctuate all over the place. I tnever seems to sit at any one point. UGH

I'll see what i come up with after moving to the 1st sensor.
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Old 06-26-2001, 07:31 AM   #9
Captain Ding
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skywalker,

The idle O2 fluctuation is normal. Mine constantly jumps around from 0 to .7V. The SAFC doesn't help until your throttle position matches that of your lo-throt position, but I check it at idle every morning just to make sure my O2 is working. BTW - I had mine set up by Rallispec. They said that .8V (might have been .82V) means the engine is running stoic, so that's what I've been shooting for. It's strange that I've had to go way rich on the SAFC to get there, and you're at the opposite end even though it's the same model year. I have a rallispec intake, borla headers and a rallispec cat-back.
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Old 06-26-2001, 12:33 PM   #10
skywalker
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The only possible issue might be that you are running it on the 2nd O2 sensor. Hmmmmm, still odd though... This is a something I heard, but aren't you suppose to add 2 bars to the final A?F Ratio for every cat the exhaust has to go through? I coudl be totally wrong...

I still need to move the wire to the 1st O2 sensor to see what I get there.
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Old 06-26-2001, 06:39 PM   #11
STiTuner
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You know what really looks cool?

an A/F ratio gauge bouncing all over the place when a car with big ass cams is just trying to idle... especially at nite.

Brad

I guess this doesn't realyl help anyone... sorry
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Old 06-27-2001, 01:32 AM   #12
Jonathan_Yi
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I thought you couldn't use the first O2 sensor because it's not wideband (or something along that line).
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Old 06-27-2001, 10:33 AM   #13
Kevin Thomas
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Default Wow! Where are the FAQs?

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!

Last edited by Kevin Thomas; 06-27-2001 at 10:36 AM.
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Old 06-27-2001, 12:44 PM   #14
jeffg
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On the MY00-MY01 RS the front O2 sensor is a wideband type Bosch. The voltage range is from .2-4.9 volts. Does anyone know what the Stoic. voltage is on this type of sensor? I tried sending an email to bosch, but got no reply yet. This would greatly help out a lot of people that are tuning their cars wrong.

Ask your friends, neighbors, everyone you know.

Jeff
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