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Old 11-06-2001, 10:20 AM   #1
pdlindor
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Question Do I need a fuel computer?

Right now my only performance mods are a GanzFlow intake + a K&N filter. I plan on adding a Stromung muffler in the next 3 or 4 months.

At what point do I need to consider a fuel computer (TCII, S-AFC) to ensure that I'm not running too rich/lean on my 2002 RS?

Is there a danger in running dangerously lean if I don't get one? Is this something that is required after a certain amount of modification?

Thanks,
~Paul
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Old 11-06-2001, 10:55 AM   #2
Iowannaski
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First of all, a TCII isn't really a fuel computer, but it probably would help some lean conditions. Not that you really need help avoiding lean conditions. Unless the 02 differs significantly from the 00-01 setups, you really shouldn't expect any problems when adding just intake and exhaust.
Everybody and their sister has upgraded the intake and exhaust on their 00 and 01 RS's without problem (excluding CELs).
If anyone knows something important about the 02 RS that I am missing, please let us know.
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Old 11-06-2001, 11:42 AM   #3
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The SAFC would do you no good anyway, except at WOT.

However, you should be fine without one. I was running an intake and exhaust on mine, and had no issues with running rich or lean
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Old 11-06-2001, 03:29 PM   #4
Blindeye_03
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Quote:
Originally posted by Impreza Rider
The SAFC would do you no good anyway, except at WOT.

I dont understand what that means...

So if I add more fuel at low rpms, even if my fuel computer says I am getting extra fuel I am not really getting that fuel?



-justin
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Old 11-06-2001, 04:02 PM   #5
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RS's tend to run rich, even more so with and intake and exhaust.

So don't worry too much about running lean.

Tats.
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Old 11-06-2001, 04:10 PM   #6
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The ECU's in the MY00+ RS's tend to learn around the corrections, and get back to the stock parameters. Once the ECU switches modes from closed loop (low throttle) to open loop (high throttle), then the AFC benefits you by allowing you to change the fuel curve.

Make sense now?
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Old 11-06-2001, 06:25 PM   #7
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Quote:
The ECU's in the MY00+ RS's tend to learn around the corrections, and get back to the stock parameters.
How can that be possible? When you wire up the SAFC you cut the wires and splice in-line so the unit can alter the readings sent to the ECU from the sensors.

So if the ECU learns anything, it is learnig what you want it to because it is adjusting to the "false" reading that you are sending it.


Tats.
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Old 11-06-2001, 06:46 PM   #8
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The MAP sensor is not the only thing used by the ECU to calculate fueling, but it is the only sensor manipulated by the S-AFC.


Ben
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Old 11-06-2001, 07:22 PM   #9
yamarocket630
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It's really quite simple. The TCII or AFC are going to modify the voltage inputs from the Coolant temp sensor, and maybe MAP sensor to fool the pcm into adding more fuel. BUT then the pcm will receive voltage signals from the oxygen sensor that tell it the car is running too rich (according to the factory programming), and the pcm will then learn (very quickly ) to not add as much fuel, so that the O2 sensor will give readings that indicate the air fuel ratio is as close to 14.7 to 1 as possible. The pcm always wants the A/F to be 14.7 to 1, as that is where the lowest emissions occur, and emissions are why you have fuel injectiion and a pcm in the first place. At WOT (wide open throttle) the pcm ignores the O2 sensor, and runs completely off of its own internal programmed fuel curve. At that point, modified siganls from the TCII or whatever will cause the pcm to add more fuel than it normally would, which SHOULD net more power. However, too much fuel is also a bad thing. Simple huh?

I've only really scratched the surface of how feedback fuel injection works, and I've tried to simplify this as much as I can, so please don't take this to be all there is to it. There are, for the sake of clarity, some slight inaccuracies in my post, but trying to make it 100% correect would take forever, and get VERY complicated.
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Old 11-07-2001, 05:35 PM   #10
DustinR
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Default Curiosity??

I'm just having a random thought on this so deal with me please. The AFC seems, to me at least, to be a very lose patch on a problem that should be solved elsewhere. Is there an aftermarket ECU out there that would let us set things the way we want them to be?? Seems like that would make more sense than patching around the problem. Also something like that would allow you to make other changes to fix problems that might present themselves through modding your car. If that sounds like a coherent thought to anyone. Go you cause I don't think it makes sense to me.

Sorry
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Old 11-07-2001, 06:14 PM   #11
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Dustin-

Yep...it's called a TEC-II. About $2200 IIRC, but you get COMPLETE control over your engine.
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Old 11-07-2001, 06:16 PM   #12
yamarocket630
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Yes there is one calle dthe Link ECU, which a few people have tried, it is a complete stand alone ecu, but not too many people from I have heard likje it, it is very hard to tune. There is also the TEC II, (go to the products page and look for it) from what I hear, it is much better, tuned through a laptop, and fairly easy to use. I don't have first hand experience with either one, so I don't really know for sure. BTW, both are Kaching!!$$$$
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Old 11-07-2001, 06:56 PM   #13
Keiho
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There isn't a plug and play unit from Link for the EJ25 as far as I know. No baseline maps, nothing.

I strongly suggest against getting a Link for the EJ25. I know they work wonders for the EJ20, but our EJ25s...that's entirely different. That's not to say you could probably get it running well, but it'll take lots and lots and lots of tuning. It'll run, but if you want it close to stock, I haven't had luck with it last time while helping a friend tune.

If you're going to spend the money for a complete standalone, get a Tec-II or Haltech.
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Old 11-07-2001, 07:47 PM   #14
DustinR
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Unhappy

good lordy dat a lotta money!!

So i guess i can scratch that thought right out of my head
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Old 11-08-2001, 06:16 PM   #15
yamarocket630
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Geez, I just read my own reply, I need to lay off the cough syrup, I musta been drunk to make that many typos!
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Old 11-08-2001, 08:53 PM   #16
JulianH
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Or you could get yourself a Unichip. Costs a hell of a lot less than a stand-alone ECU, but gives you almost as much tunability, epecially if you are staying N/A. I think they run somewhere around $600. Talk to Shiv, Cobb Tuning, or TurboXS.

JulianH
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