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Old 04-08-2002, 11:47 AM   #1
phucvtec
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Member#: 16261
Join Date: Mar 2002
Location: Buffalo, NY
Vehicle:
2000 Impreza 2.5RS
Blue Ridge Pearl

Unhappy S-AFC trouble

I have just completed the instalation of a S-AFC in my model year 2000 impreza rs. I also have the following mods:

Cobb tuning CAI
Borla Headers
Random Tech high flow cat
Stromung 2.25" intermediate pipe
Stromung dual tip muffler

Here is my problem. There are no problems opporating the vehicle, however as soon as I started up the vehicle, I got a CEL (I had one for a long time before as well, and Im told it is because of the wide band O2 sensor - emmisions sensor). Also, I immediately noticed that the pressure signal was reading improperly. The readings I got ranged between -755 torr and -745 torr. Obviously, these readings do not make sence. I also used the sensor imput moniter function to see if the 1st imput chanel was working, and i saw readings between .5V and 4.5V as the throttle was toggled. For the record, I set the S-AFC to the following settings PRIOR to starting the vehicle for the first time:

sensor type: 5 in, 5 out
throtle type: increasing
cylindars: 4 (obviously)

Instalation went quite easily, and I had help from someone well skilled in electrical assemble, so I highly doubt that there is a wiring problem. What type of pressure signal should I suspect? I really need to figure this out before I attempt to tune, so any insite would be greatly appreciated. Thanks!!!
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Old 04-08-2002, 11:58 AM   #2
tmat3
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I can't answer your question fully until you get the CE code scanned, but here is what you can do to possibly eliminating the CE light.

Initialize the SAFC.
Take the - terminal out for a few hours to reset the ECU.
Reconnect the battery.
Set the SAFC again (your setting is good : Pressure, 5 in/5 out, Ascending throttle, 4 cylinder)
Start the engine.

If it doesn't solve the problem, check the MAP reading. It should be reading somewhere around 650mmHg during idle. Then, check all wires for any loose connections. You didn't mix up the white wire and yellow wire, did you?
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Old 04-08-2002, 01:36 PM   #3
phucvtec
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Thanks for the advise. During instalation, I had the batary cable disconnected for about 2 hours, so I figured that was enough time for the ecu to reset. I'll try again. As for the CEL, I do not know how to get the vehicle to display the code, and I suppose I would not know what it meant anyway. Perhaps I will visit the dealership. The CEL started when I purchased the header and high flow cat from Cobb Tuning. They told me it was because of errant readings comming from the second O2 sensor, however I do not know how having the CEL will effect vehicle opporation. Will it force the ecu to run in open loop mode?

Oh, and Im am pretty darn sure that I hooked up the wires correctly, however, it would make sence that they were connected in reverse, since the pressure signal im reading looks like the opposit of what I would expect. I will have to rip it apart again

Thanks for you help!!
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Old 04-08-2002, 04:57 PM   #4
Poppa smurf
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IIRC the CEL on the MY00 was because of the random tech cat. Itís called catalyst inefficiency or something should be the code youíre getting. There have been a couple threads about it and I think a fix was wrapping your headers. I have a MY99 running the same set-up but maybe someone with a MY00-01 can chime in and fill you in a little better. BugBomb perhaps anyone?
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Old 04-08-2002, 05:28 PM   #5
phucvtec
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I just checked, and I did hook up the presure sensor wires correctly. I think I may have had one of the settings incorrect however. I must have accidentally changed it when I was fooling around Anyway, I have removed the batery cable again, and I will try to set it up again after I let the computer reset. Thanks for the help!
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Old 04-09-2002, 12:05 AM   #6
Daveish
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Um, just a theory...

When the engine is throttled, the cylinders need to suck air from the outside into the engine. Hence one would expect to see a pressure gauge returning a negative pressure.

By the same token, the only time you would see a positive pressure is when air is being forced from the outside into the cylinders (e.g. with forced induction, turbo or SC).

Of course, I could be totally wrong, but it's a possible explanation to your negative pressure readings.
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Old 04-09-2002, 12:45 AM   #7
phucvtec
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Smile

I agree 100%. It seems that I am seing the opposit signal that I expected, or in other words, I am seing
(what I would expect) X -1
For instance, sorta along the lines of what you had said, I would expect to see the pressure move from around ambiant (760 torr) to a value lower than that as the throttle is depressed and a vacuum is extablished. However I see the pressure reading on the S-AFC change from -760 torr at idle to around -50 under throttle. I guess the take home message is that I should just know more about the product before I attempt to diagnose a reading that I did not expect to see

Thanks for the help
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Old 04-09-2002, 09:42 PM   #8
munkis
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My 2 cents is the high flow cat is what is causing your CEL and not the safc.

I have an safc on my 2000 RS no problems...

IIRC..did you hook up the brown wire closer to the ECU like it said in the directions.

I still would say its the cat. the paramaters in the ecu, are set for the amount of flow the stock cats should produce at any given time...

It will recognize the higher flow through the cat as the cat not doing its job correcttly...it sees it as 'too much flow' = malfunctioning cat...

thats the easiest way I can explain it without getting all technical.

a code would really help us here .

you dont have any low throttle corrections do you? it does nothing on MY00 - 01 cept throw ce lights. You should be sticking with high throttle correction only.

oh and technically air is not 'sucked' into the engine. It is and it isnt.

the vacuum created by the pistons moving creats a lower pressure inside the engine hence neg pressure...its like weather, high pressure always moves into lower pressure, so in a sence air is actually 'pushed' into the engine...make sence? I think I got that correct...

Jay McDade
Auto Tech -- Lincoln/Mercury/Jaguar
www.hometown.aol.com/impreza25rs2000
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Old 04-10-2002, 09:58 AM   #9
phucvtec
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Blue Ridge Pearl

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hmmm... yeah, I have double checked the wiring connections, and they are all correct. One interresting observation I have made comes from "checking the sensors" with the S-AFC. I only have imput channal 1 hooked up obviously, however imput channel 2 shows about .5V. Inductance perhaps? I really don't think it mattters anyway. As for the CEL code, I will have to go to the dealership in the near future. Also, I have not begun to try to tune the vehicle, since I am not 100% comfident that the S-AFC is working correctly. Thanks for the heads up on the "low throttle settings". I am also in the process of installing an EGT guage for tuning. I figure I need some sort of data output before I start modifying opporating parameters. Thanks again, and I will likely post again when I get the CEL code.
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Old 04-10-2002, 12:24 PM   #10
munkis
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rallyarmor.com

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good deal with the EGT, its a must for proper tuning of the s-afc.

ill do the sensor check thingie with my safc and see what it reads for you.

I have never played with it though.. lol.

Jay McDade
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Old 04-15-2002, 10:19 AM   #11
phucvtec
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Blue Ridge Pearl

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Thanks alot! I have a feeling that the S-AFC is actually working properly, now that I have reset the ecu (again) and properly set the settings. I think that I am just having trouble interpreting the pressure readings. *negative pressures just don't make a lot of sence to me In any case, I would appreciate it if you could post after you have checked your sensors. Thanks!
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Old 04-15-2002, 06:10 PM   #12
Daveish
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Quote:
oh and technically air is not 'sucked' into the engine. It is and it isnt.

the vacuum created by the pistons moving creats a lower pressure inside the engine hence neg pressure...its like weather, high pressure always moves into lower pressure, so in a sence air is actually 'pushed' into the engine...make sence? I think I got that correct...
FWIW...

I've always learned that air is pushed or pulled depending on the object that causes the pressure imbalance; e.g. a supercharger is an external device pushing air into the engine -- the engine has no need for the volume of air being forced into it, hence it is being pushed in -- whereas the movement of the pistons induces a need for air from the vacuum it creates, and so air is pulled into the engine. It just matters where your point of reference is -- in my case, it was the engine. Of course, if your reference point were the outside ambient air, then I'd believe you would be correct. Then again, it's been awhile since I've taken my fair dose of physics.

Well, same end effect, however you describe it.
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Old 04-15-2002, 08:39 PM   #13
munkis
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crap i knew I forgot something, Ill do it 2morrow morning.



jay
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