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Old 01-05-2009, 04:55 AM   #1
02CWRX
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Default Mystery Wires Under My Hood... Ideas?

I have an 02 WRX with an Invidia EL header (integrated up-pipe), and catless turbo back exhaust. These were installed by the previous owner.

I was poking around under the hood the other day, and I found a single wire coming out of the firewall near the cruise control motor thats about 2" long with no plug on the end. Its definately OEM wiring, but I see nowhere it should go. It looks like it might be ripped off, or cut. What Im trying to figure out, is if it was the stock EGT probe I keep reading about? Maybe its the reason I get such poor gas mileage. No matter what I do, I cant seem to break 16 MPG city in the car... Then again, Its not fully tuned yet and runs rich.

Anyway, I know it has a couple O2 sensors installed at least, and theyre not just bypassed, but this mystery wire has me intrigued. Even if its not the EGT, or the reason for my crappy mileage, Id like to know what its for so I can take care of it properly if its no longer needed. Everything else on the car is installed neatly and professionally, so Im just a little curious of this wire. Oh, and yes, the cruise control works correctly. The only thing that doesnt work in the CC system, is the fact the light in the switch doesnt light up when its on. But, I kind of doubt this wire is responsible for that.

So, is the EGT probe a single wire or multiple like an O2 sensor? Does anyone have a picture that shows the EGT probe, or the wire(s) that used to go to theirs? Any idea what the single wire might be?

~T.J.

EDIT: Also meant to say that everything else on the car works perfectly with no problems, so whatever it is, it isnt making itself obvious. The only thing the car has a "problem" with, is the fuel mileage, which hopefully will be taken care of once the AccessPort gets here. For now, its running 10 PSI of boost, which could justify the rich running.

EDIT X2: Heres a picture. It seems the wire doesnt actually come out of the firewall. Instead, its "doubled back" along the harness back towards the firewall from where it branches off the main harness, around the BCS area. This leads me to believe its supposed to go to something more in the cylinder head/engine block area. The wire looks to be red with a yellow stripe.
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Last edited by 02CWRX; 01-05-2009 at 06:41 PM.
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Old 01-05-2009, 07:50 AM   #2
StupidFastWagon
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The stock o2, EGT wires are cliped on a metal post near the stock BCS. The wire might before something aftermarket... I would look under the dash to see what it goes to.
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Old 01-05-2009, 08:40 AM   #3
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It's not your EGT probe. That probe threads into your Up-pipe, near the turbo, then has a short (~8in), two-wire run to a small, grey, square connector, which plugs into the main harness in the engine bay, right next to the other 2 connectors under that little plastic cover plate. It's right above the boost control solenoid. If you look, there will be three connectors there. One is large, and one of 2 main harness connectors, and the other 2, in decreasing size, are the front O2 sensor, and the EGT sensor.
Unfortunately, I don't have a clue what that wire is, but I wouldn't rule out that it might be related to the light not coming on. Sorry.
-Mateo
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Old 01-05-2009, 06:34 PM   #4
02CWRX
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I went and snapped a picture today. It looks like the wire is actually much longer than I suspected. It appears as if it branches out of the main harness about where the BCS is on the inner fender, but its been doubled back along the stock harness it comes out of, (back toward the firewall) and zip tied down. The wire appears to be red with a yellow stripe.

Also, how many O2 sensors do these cars have stock? Two, right? Front and rear, and then the EGT probe? I just got to looking, and I have one new OEM Denso sensor as the PO told me, but the other one which I THOUGHT was an O2 sensor, doesnt look like an O2 sensor at all. Maybe thats the stock EGT probe? If thats the case, where is the plug for any other O2 sensors the car might have? Its it really far up front? The plastic cover for my BCS is missing and the only plugs in that area are the one big main harness plug, and two smaller ones, one for each of the two sensors I just described. Ive included a picture of my up-pipe area as well. Remember, its an Invidia EL header with an integrated up-pipe. The way the picture is taken, is from the firewall forward, so the turbo would be at the top of the picture.

I also included and overall shot of the engine bay and the car, just for fun

Thanks for any help!

~T.J.

Mystery wire:


O2 & EGT Probe?


Underhood:


Car:

Last edited by 02CWRX; 01-05-2009 at 06:43 PM.
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Old 01-05-2009, 06:43 PM   #5
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those are egt and o2... the one with 4 visible wires on it is the o2, the other is the egt... no clue what that wire is, but I would check anything that has sensors - tgvs, etc...
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Old 01-05-2009, 06:47 PM   #6
02CWRX
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Strange that they would go so out of their way to not hook it back up, whatever it was (zip ties)... Im not too familar with these engines yet, what sensors are on the passenger side of the engine in the cylinder head area? Oil pan even maybe?

I know for my Toyota, I have a diagram of the engine as a plain outline, with all the sensor locations pointed out in more detail. Anything like that for the WRX floating around online?

~T.J.
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Old 01-05-2009, 06:54 PM   #7
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somebody was a REAL idiot there

you need a 2.2k ohm resistor in the egt circuit
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Old 01-05-2009, 07:07 PM   #8
02CWRX
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Whats the point of that if the sensor is still in place? I could see doing that if there was no place to install it...

Oh, and I found a copy of the service manual, so Im poking through that for sensor locations.

~T.J.

EDIT: Well, I went out and looked for the only sensors I thought it could be, and after some MORE looking, Im starting to wonder if maybe its routed the way it was from the factory. Its taped down to the harness in the same places the cruise control solenoid is taped, and after thinking about it, the zip ties were only to keep the O2 sensor wires from moving into the downpipe. So, Im back to square one. I wish I knew anyone with another WRX so I could just look to see what else is in that area since I know exactly what I would be looking for.

Last edited by 02CWRX; 01-05-2009 at 07:38 PM.
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Old 01-05-2009, 08:37 PM   #9
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Thats a different uppipe, looks like they crappily welded the egt bung there and its not even in the stream. The o2 sensor goes down in the manifold, so Im asumming theres an ebay special down there. As for the wires..who knows.
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Old 01-05-2009, 08:45 PM   #10
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It goes to an unused connector. I have the same thing but it still has the connector on the end. It's taped to the factory harness. Probably for an option we don't have.
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Old 01-05-2009, 08:57 PM   #11
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The red wire with no end on it looks like the one that goes to the extra horn some had. It would have been bolted to the top of the strut. It gets removed a lot when adding a strut tower bar. At least I did anyway.

The upipe is a little scary looking, but as long as it doesn't leak...
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Old 01-05-2009, 10:09 PM   #12
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Quote:
Originally Posted by 02CWRX View Post
Car:

Not trying to thread jack, but are you running 2 different color wheels for those FN01R's or is that just the lighting?
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Old 01-05-2009, 10:17 PM   #13
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Quote:
Originally Posted by BluScubi View Post
It goes to an unused connector. I have the same thing but it still has the connector on the end. It's taped to the factory harness. Probably for an option we don't have.
Quote:
Originally Posted by 69subaru360 View Post
The red wire with no end on it looks like the one that goes to the extra horn some had. It would have been bolted to the top of the strut. It gets removed a lot when adding a strut tower bar. At least I did anyway.

The upipe is a little scary looking, but as long as it doesn't leak...
OK....thats right...the oem alarm had the horn attached in that area

but still.....anybody that put the egt sensor in that setup just didnt know what they were doing as there is no need for it at all
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Old 01-06-2009, 02:31 AM   #14
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That is for the horn that is bolted to two of the strut mount bolts. I still have mine and the wires wrapped in the plastic coat look just like that! Why would they just not uplug the clip?
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Old 01-06-2009, 09:19 AM   #15
02CWRX
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Quote:
Originally Posted by scby rex View Post
Thats a different uppipe, looks like they crappily welded the egt bung there and its not even in the stream. The o2 sensor goes down in the manifold, so Im asumming theres an ebay special down there. As for the wires..who knows.
No eBay special. The EGT port is stock on the equal length header (which has a built in up-pipe, all one piece. See picture). It looks like the probe is welded to an adapter which is then threaded into the header. The pictures dont show it well. Either way, I know it looks hokey, but there are no leaks. I guess the welds are just there to keep it from backing out.




Quote:
Originally Posted by flukewrx View Post
Not trying to thread jack, but are you running 2 different color wheels for those FN01R's or is that just the lighting?
Lighting, theyre all silver.
Quote:
Originally Posted by SUBIEWRX03 View Post
That is for the horn that is bolted to two of the strut mount bolts. I still have mine and the wires wrapped in the plastic coat look just like that! Why would they just not uplug the clip?
After I got off here last night I found a very helpful section in the manual that also said the single wire was for a "security horn". Im just a little confused however because I have the factory alarm, and it works. Im guessing there was an additional horn to the stock one that used to go there and would sound as well when the alarm was activated? Someone mentioned its commonly removed when a strut bar is installed, and that would make sense seeing as I have one. My VW had a horn in almost the same spot in addition to the stock one, and both would sound when the alarm was going off.

Well, sounds like another mystery solved. Thanks for the input. I will be cutting the exposed wire off and heat shrinking to prevent "shorts" and clean it up. I also found I have the rear O2 sensor is in fact further back in the exhaust. So, the "front" sensor is in the up-pipe, and the "rear" is after the downpipe.

What would the benefits be to the resistor in the EGT probe area? Anything?

~T.J.
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