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Old 01-13-2009, 03:32 AM   #1
Scooby Newbie
Member#: 195779
Join Date: Nov 2008
Chapter/Region: NWIC
Location: PNW
1999 Legacy 2.5GT

Default '97 Legacy Intake Issues

Recently me and my friend attempted to make a DIY intake for my 97 Legacy (automatic). Being young and impulsive, we dove in head first without doing any serious research beforehand - believing that the resonators along the intake were purely for acoustics. I have now read through Williaty's thread on MAF's and Heimholtz resonators used to prevent errors in reading multiple times, as well as numerous other threads on NASIOC and other Subaru boards.

I believe that I understand the problem Williaty has discovered well enough, and assume that is it the problem that I discovered with my car simply because I do not know what else it could be. However (at least according to my butt dyno) it does not seem to match exactly what Williaty described.

First I want to say sorry for how long this post will end up being and thank you to anyone willing to read through it all. Second, in order to describe the problem thoroughly, I will use a timeline of sorts.

When my friend and I first modified my intake, we simply removed the snorkus - believing it to be purely for acoustics - and had a pipe sticking a short distance down into the fender from the filter box. With this very small change the car seemed to run just as well as stock, and it even gave me a sense of a small improvement (although I would guess it was simply a placebo effect). No apparent problems with idling, WOT, anything.

Encouraged by this, we decided to remove the remaining two resonators on the accordion pipe and torque box (we replaced the torque box with the box from my friend's 2001 2.5rs, which had no apparent resonators). After we hooked all of this up (it looked quite nice ), I attempted to start my car only to have it idle for about 2 seconds and then start dying. I'm not sure how to describe it perfectly, but the tachometer was swaying wildly and the car was bucking pretty hard before the car would die shortly thereafter.

The first thing we tried was to reset the ECU by disconnecting the negative battery terminal and pump the brakes to drain all the power from the system. We let it sit like this for about an hour before reconnecting the battery and starting it up. This time the car would idle, although poorly (the tach was still swaying quite a bit and you could hear the engine struggling some), and just to test it we tried to drive down his driveway. The car seemed like it could die at any second but kept running as i backed out of his garage. Then as I started to drive forward it seemed down on power and I gave it nearly full throttle. It picked up RPM's until about 3k at which point the car bucked a couple times and died. I was able to start the car immediately back up and drive it carefully back into the garage.

After much contemplation and being unable to come up with any answers, we began scouring the Internet for answers. This is how I first found NASIOC and Williaty's thread on MAF resonance issues. This seemed to be the only answer as far as we could tell, and being stubborn in admitting defeat to the resonators we attempted to build the cai down into the fender and place a cone filter there instead of using the stock one inside the filter box. This attempt to manipulate the resonance seemed to payoff to the point of the car no longer dying at any point. We drove the car around for a while but there was still obviously something wrong as it the car would be noticeable down on power between 3k and 4k rpms and would the tach would still drop quite severely at some points.

At this point we decided to admit defeat and put the accordion and my torque box back on along with their resonators. When we did this, we chose to leave the piping in the fender on along with the cone filter. The car seemed to be back to the way it was before all of this for the most part, but on the 30+ minute drive back to my house I could tell that it still wasnt quite right - it still seemed to not be running quite as well and slightly down on power (of course this was all according to my very inaccurate butt dyno once again). Once I returned home i proceeded to take off the cone filter and replace it with the stock panel filter back inside the filter box. This is the way it sits as I type this post, and it seems to be running perfectly well to my untrained butt dyno.

While I still have not come up with any answers to this problem besides MAF errors due to resonance, I am also not wholly convinced that is the problem. This is because in Williaty's thread, he explains that the snorkus is the crucial resonator throughout the intake tract and to leave it be - while removing the accordion and torque box are part of his hybrid intake design. However in my car, the snorkus was the first part we removed and I have yet to put it back in my car to this day. Nonetheless my car, as far as I can tell, is running just as well as it did without the snorkus (but with the accordion and torque box resonators still present). Another issue I see is that Williaty described MAF errors which occurred below 2k rpm and at or near WOT, which I have seen none of (I realize that doesn't mean they aren't there, though). All of the issues which I experienced occurred during idle and at roughly 3k rpm.

At this point I am looking for an answer almost purely for knowledge's sake, as I have been humbled by the hidden complexity of even the most modified parts of a car as well as the extensive knowledge of so many here at NASIOC.

Thanks to anyone who has actually put up with my rambling and read through this enormous post - sorry to have taken up so much of your life, hahah.
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Old 01-14-2009, 03:53 AM   #2
Scooby Newbie
Member#: 195779
Join Date: Nov 2008
Chapter/Region: NWIC
Location: PNW
1999 Legacy 2.5GT


bump? (read the forum rules and I think I'm allowed to bump? within reason of course)

no one?
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Old 01-14-2009, 07:34 PM   #3
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Chapter/Region: South East
Location: Central Floriderp

when i originally installed my SRI, i noticed no loss of low end power but i never really looked for it. And then after williaty's theory and later writeup about the hybrid intake, i tested my SRI. sure enough, the MAFv error was there. So without doing a proper test, simply going by feel doesn't mean there isnt a MAFv error and a resulting change in fueling. weather its bad enough to do damage in your case is unknown until a MAFv test is done. Unfortunately, i dont know of any way to log a pre 02 ECU, so you may not even be able to do such a test.
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Old 01-15-2009, 02:03 PM   #4
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Join Date: Jan 2008
Chapter/Region: NESIC
Location: Portland Maine
2007 ej253n/a 5speed
Red Sox Nation Lifer


i run an sri right now but have many other mods and have not run the test conclusively yet maybe i will today , but, when i installed my intake i had major issues.

you have to rescale the maf if you want to drive our car without bucking and what not
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