I apologize if this has been covered before but I tried searching everywhere (i-club, nasioc, scoobymods, google) and couldn't find an answer that fit what I'm currently experiencing.

Last week I got a catback exhaust (Borla Hush dual tip) for my 02 wagon and have been experiencing a weird chirp/flutter/high pitched "psssh" noise along with an engine stutter (almost like fuel cutting out--not that I've knowingly experienced that-- but basically it feels like a momentary hesitation). It sort of sounds/feels similar to when you turn on your AC while driving under load... if you know what I'm saying. Anyway, this happens momentarily (like a second) and then all is well afterwards. The noise sounds like its coming from directly underneath the driver's seat.

The noise/stutter only seems to happen when I'm off boost and/or under light throttle (such as while cruising or slowly decelerating) and happens several seconds following my last gear change and/or acceleration . The noise is noticeably different than what I experience when letting off the gas under load to shift (i.e. the BOV "psssssh"). Also, I've come to the conclusion that this is not wastegate flutter since that seems to occur only while boosting (according to what I read).

My engine is stock except for the catback exhaust and snorkelectomy (which occured years ago, so I familiar with the noises associated with that mod).

Anyone know what is causing this noise/stutter? Is it considered normal and has it only become noticeably due to the catback? Or is it related to a possibly exhaust leak?

 

No CELs? If you have a boost gauge, do the boost and vacuum readings appear normal as you drive?

A minor exhaust leak after the downpipe would not cause this much of a problem.

Have you checked underhood for obvious cracked hoses or loose fittings?

--
0==WW==0
"…axles of evil…" - george w. bush

 

No recent CELs (past ones were for cylinders misfiring over a year ago). Turbo gauge activity appears to be normal.

I just checked under the hood and all seems pretty normal (at least to my untrained eyes). I did recently bring my car in for 60k service at the dealer... in fact it was the day before I got the Borla installed. I don't recall noticing this problem prior to getting the Borla.

 

hmmmm, that sounds very familiar to me.....My car does something similar to this on occasion, particularily when I am accelerating (from a stop, or just speeding up)...I get a moment of hesitation, then some fluttering, then it all smoothes out, when under decent load. However, my problem is caused by the boost lines that control the wastegate. They are all chapped from the heat generated by the turbo, the rubber dried out and the hoses cracked, causing a vacuum leak between the Boost control solenoid (BCS) and the wastegate actuator. I temporarily fixed the hoses (with duct tape, yes it fixes everything) so I can still drive the car, but it still acts like that every now and then.

See, whats happening, is when the BCS tries to open/close the wastegate the vacuum/boost pressure in those chapped lines is leaking out and the wastegate cannot react properly to the input from the BCS. So you get that momentary hesitation/fluttering until the boost pressure builds enough to work properly. Like I said, I temporarily fixed the problem by wrapping the chapped areas of the boost lines with duct tape to seal them, but I will be eventually installing the Perrin Electronic Boost Control Solenoid (Tuning required with the install of the EBCS), so I will be replacing all of those lines with Silicon ones anyways, and the problem should disappear alltogether.

Hope this helps you out..... Here's a link to WRXF where I posted a picture of the Boost lines I am talking about, so you can see where they are located. http://www.wrxfanatics.com/index.php...ic=30805&st=15

You'll notice the part that "T's" off from the Turbo is the line that connects to the Factory BCS.....Check ALL of these lines for cracks, holes, tears, or any form of leaks. They are Boost/Vacuum lines, so you wont see any "drips" or anything, you have to physically inspect each line visually for cracks.

-Ted

EDIT: BTW, this did NOT throw any CELs on my car either.

 

Thanks for the info, Ted. I'll check the lines when I get home tonight. Based on your diagnosis, would this problem occur only during acceleration, and/or only while boosting? My problem seems to occur only under vacuum conditions, and not while accelerating (i.e. I get it while maintaing speed or decelerating)

 

Hmm, maybe my car doesn't exhibit those issues because I replaced my boost control vacuum hoses with silicone lines last year. I know that as underhood heat increases as with a turbo engine, the hoses are more prone to failure.

Besides the Perrin solenoid, EQ Tuning also markets a solenoid with faster response. This item also requires tuning. I do not know how it compares with the Perrin piece.

--
0==WW==0
"…axles of evil…" - george w. bush

 

Burndtjamb - mine does it mainly while maintaining a constant speed, or accelerating.....but the holes in my lines are very minimal (after my McGyver patch job).....a line with a bigger hole or may cause the wastegate to act weird while decelerating as well. I'd atleast check it out....because the stock lines get all hard and brittle from the heat of the turbo, and can easily crack.

Wingless - Yes, you are correct, EQ Tuning is marketing the GM Boost control solenoid that was from the Cyclone and Typhoon trucks. It is essentially the same thing as the Perrin Piece.....but I think its costs quite a bit less. IIRC the Perrin EBCS is = $80-$100 and the GM Piece is like $25-50.

-Ted

 

So I wasn't able to find any obvious holes or cracks in the rubber hoses, however they do appear to be brittle and hard.

When you guys hear the chirp/whistle/flutter noise while driving, where does the sound appear to be coming from? Does normal wastegate flutter noise originate from the front passenger side, close to where the turbo is?