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losing boost at revs 4th/5th
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Old 21 Jan 2014, 05:49 PM   #1 (permalink)
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losing boost at revs 4th/5th

Hi

just bought a 1996 GC8 impreza WRX which seems to lose/wastegate out boost on revs, mainly in 4th and 5th, (well thats when its noticeable)

With WOT, it starts to boost, then eases off, then reboosts, then eases off. accelerating all the time.

i have a video of it but cant seem to find out where to upload it.

Engine is stock apart from a dump valve and a decat front pipe.

Engine runs smooth at all other times

From research so far, and general knowledge (im a mechanic,but not had too much experience with scoobys) Im thinking its got to be just opening the wastegate, but why. Faulty solenoid maybe?

cheers for any help

Wayne
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Old 21 Jan 2014, 06:52 PM   #2 (permalink)
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Re: losing boost at revs 4th/5th

try stock Dump valve, has it got a decat downpipe ?
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Old 21 Jan 2014, 08:09 PM   #3 (permalink)
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Re: losing boost at revs 4th/5th

Hi bob, I don't have the stock valve, but I do have another one I could try. I can't hear it releasing when the surging happens though.

Is there a way I can upload a video?

Edit - yes has decay downpipe

It's a forge dump valve btw

Last edited by pikey; 21 Jan 2014 at 08:18 PM.
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Old 21 Jan 2014, 08:25 PM   #4 (permalink)
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Re: losing boost at revs 4th/5th

Quote:
Originally Posted by bugeye_bob View Post
try stock Dump valve, has it got a decat downpipe ?
Just in the process of fitting one.

Something we did notice though when we took the old down pipe off, there was a large hole in it near the centre pipe joint end.

Last edited by pikey; 21 Jan 2014 at 08:39 PM.
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Old 21 Jan 2014, 08:49 PM   #5 (permalink)
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Re: losing boost at revs 4th/5th

if it has a decat you could be getting boost spikes, the ecu is seeing too much boost and pulling it, then allowing it back again,
Or if your hitting too much boost you could hit fuel cut, but thats more a brick wall hitting feeling so Id guess it isnt that.
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Old 21 Jan 2014, 09:09 PM   #6 (permalink)
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Re: losing boost at revs 4th/5th

Quote:
Originally Posted by bugeye_bob View Post
if it has a decat you could be getting boost spikes, the ecu is seeing too much boost and pulling it, then allowing it back again,
Or if your hitting too much boost you could hit fuel cut, but thats more a brick wall hitting feeling so Id guess it isnt that.
So is that a mapping job to cure it?
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Old 22 Jan 2014, 09:28 AM   #7 (permalink)
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Re: losing boost at revs 4th/5th

nah normally a fiddle with the boost pill will sort it for spikes, or if your hitting fuel cut fit a Fuel cut defender,
Boost as a word means very little so I cant tell you what you need to do until we know what "your boost" is doing.
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Old 22 Jan 2014, 02:59 PM   #8 (permalink)
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Re: losing boost at revs 4th/5th

i couldnt find the boost pill, but there was a plastic cylinder type unit in the line. pic attached.

also a couple of other pics


after a bit more research, is the pill in the bottom hose on the BCS? the lower pipe visible in pic2?
Attached Images
File Type: jpg IMAG1314.jpg (57.1 KB, 3 views)
File Type: jpg IMAG1315.jpg (76.0 KB, 4 views)
File Type: jpg IMAG1313.jpg (47.6 KB, 3 views)

Last edited by pikey; 22 Jan 2014 at 03:11 PM.
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Old 22 Jan 2014, 03:28 PM   #9 (permalink)
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Re: losing boost at revs 4th/5th

you want to hook a boost gauge up and see what is actually happening, then whip up the carpet and see what ECU it has fitted,
we then compare what boost it should have and when compared to what is happening.
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Old 22 Jan 2014, 05:17 PM   #10 (permalink)
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Re: losing boost at revs 4th/5th

will do
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