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Old 05-30-2000, 11:37 AM   #1
RSRacer
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Cool ZEX Nitrous Kit for Impreza

Okay, I ordered my ZEX kit today, will be receiving it Friday if all goes well. So now I have a question... The ZEX kit is supposed to be for a Honda. However, I own a 99 2.5RS. I know that installation will be a breeze, but my concern is with two things:

1.) Will the TPS voltage be compatible with that of a Honda? The TPS voltage is used to trigger nitrous flow with this kit. Obviously, the voltage at WOT must be very similar for the Honda engine for this to work on my Subaru.

2.) What about the vacuum line to bump up fuel pressure? The ZEX controller raises fuel pressure while injecting nitrous. It does so using a vacuum line, I believe. Will the vacuum hookup for a Honda be compatible with my Subaru engine? I mean, will I be able to just hook up the controller to my fuel injection system without any problems?

Has anybody on this board installed a ZEX kit on a 2.5RS before, or even heard of it being done? I am willing to be the guinea pig here, but I sure don't wanna blow my engine!!!
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Old 05-30-2000, 01:02 PM   #2
Memnoch
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Maybe someone in the Technical Forum can help.
 
Old 05-30-2000, 01:36 PM   #3
rao
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The TPS signal at wide open thtottle is 4.2-4.7 volts for a 2000 Impreza RS, it is likely the same for 99's and 98 RS' as well. I have no idea what a honda's TSP voltage is. The fuel pressure riser should work the same way that a Honda does.

You need to find out the answers to these querstions for sure befoe you install the nitrous system or you will just be buying trouble.
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Old 05-30-2000, 01:56 PM   #4
RSRacer
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Smile

Thanks rao! Hmmm, I have the S-AFC, I don't know why I didn't think of the TPS reading under "Sensor Check"! Yes, mine reads about 4.2 at WOT. Come to think of it, the AFC may answer the question about TPS voltage. The S-AFC works for Honda's and Subaru's, and considers the reading of 4.2 volts from the TPS to be WOT (100% thr). So I guess that's standard? The only configuration option for the S-AFC regarding the throttle sensor is whether it is an ascending or descending throttle setup (ascending in both Honda's and Subaru's). So maybe I have answered my own question about the TPS.

Anybody know where I can find the info on the fuel pressure riser? I would need to know where I tee in that vacuum line. I have no idea where to start looking...
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Old 05-30-2000, 02:02 PM   #5
rao
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It is pretty easy to find, just look for the fuel pressure regulator - it is on the passenger side just to the rear of the head. It is fairly small and has a fuel line and a vacuum line running from it - just follow the line from the injectors and you'll see it.
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Old 05-31-2000, 12:53 AM   #6
RSRacer
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Keeping this near the top. Please, somebody answer!
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Old 05-31-2000, 08:29 AM   #7
RSRacer
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Hmmm, am having a little trouble finding the fuel pressure regulator. What does it look like? Is it that brass-colored thing that is right next to the fuel rail on the passenger side? rao, you had mentioned that it is behind the passenger-side head? I guess that brass thing is kinda behind the head... I am confused.
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Old 05-31-2000, 09:17 AM   #8
rao
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Well I don't have a picture, and I am going from memory, but it is brass colored and about 1 1/2" in diameter and it a fuel line running into it, a fuel line running out of it and a vacuum line running out of the top. I believe that it is on the passenger side of the engine just above and behind the cylinder head. If you follow the fuel line exit at the back of teh head, ther is a hose that leads to it and the hose from it is the return line that runs back to the tank.
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Old 05-31-2000, 09:28 AM   #9
RSRacer
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Talking

Ahh yes, I found it! Thanks for the info rao! I talked to ZEX this morning again, and got some detailed info. They said that the ZEX controller has two vacuum line hookups, which put the controller in between the vacuum source (the intake on the Honda for which the kit was designed) and the fuel pressure regulator. This way, it can bump up the pressure while injecting. And the TPS signal triggers injection at exactly 4.3V.
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Old 05-31-2000, 10:33 AM   #10
RSRacer
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Hey rao! I got another question you might be able to answer... My TPS is only sending 3.9V at WOT. The ZEX kit engages at 4.3V! So this will not allow me to actually run the nitrous! Could it be that I need to adjust my TPS? If so, would I also need to adjust idle? Does our engine have an idle adjustment screw? Sorry for all the questions!
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Old 05-31-2000, 11:27 AM   #11
rao
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That's ok, though I will only be around here for another day or so so get 'em in quick!

The spec for 2000's TPS is 4.3-4.7 volts at WOT. If you have less it should be adjused to be within spec, but that is not a task you can just easily do yourself without the manual. I would take it to a dealer or find someone with a manual locally.

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Old 06-01-2000, 12:27 AM   #12
RSRacer
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I am taking it to my dealership tomorrow. One of the mechanics said he'll adjust it for me. He has a SelectMonitor! Wish I had one...
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Old 06-01-2000, 11:31 AM   #13
skidplatez
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Cool

please keep posting your progress or email me your results I am very interested in the zex system but had thought it was for honda only. I think that non-turbo mods are the way to go because this car came non-turbo and it is kind of cool to have one of the only non-turbo performance imprezas around (north america vs. other localities) and it is way cheaper.
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Old 06-01-2000, 11:41 AM   #14
RSRacer
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Well, the TPS is sending 4.13V at WOT. It needs adjustment. My mechanic is going to do the adjustment for me. The voltage needs to be at least 4.3V at WOT to trigger the nitrous. So I will get this adjusted and let you know how it works.
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