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Old 06-05-2007, 02:35 AM   #1
twizzstyle
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Default Boost oscillation problem

I've come across a few threads dealing with what seemed to be a similar situation, but no solutions.... I'm completely stumped myself.

So the story...

I put an STi intercooler in my car. When doing so, it broke the hose on the wastegate that had become hard and brittle over time from the heat from the turbo. I noticed it the next day when my boost spiked to like 20psi I went to a local auto parts store, and got the closest hose I could get to the stock stuff, it was slightly smaller in diameter. I replaced all of the hoses except the long one from the boost solenoid, I forgot to put the restrictor pill in.

I think the smaller hose acted as a restrictor, so without the pill I was still getting about 13-14psi (was on the Cobb OTS stage 2 map, so should be more like 16 psi)... no worries, I drove it like that for a few months.

Finally I got around to getting the correct hoses from the dealer. I replaced all of the hoses, including the one going from the T to the solenoid, with a new restrictor pill, and the 1/8" coupler between the long hose and the short hose on the T.

Now the problem.... Boost will fluctuate up and down. It doesn't really happen in the lower gears, but is very noticable in 4th and 5th gear. It will do it under full throttle, and partial throttle. If under full throttle, it will peak to slightly over target boost (about 17-18psi) then back down to say 12psi, then up again. It is relatively slow (maybe 1 cycle per second) and the amplitude gets smaller with each cycle such that it settles on target boost.

I thought, well maybe the car just needs to relearn itself now that it has the correct hoses....

This past weekend I got a protune. The problem did not show itself on the dyno, but on the drive home from the shop, it was still there. So I know its not the map.

From my conclusion it points to something mechanical... but I can't figure out what. I've double checked the hoses 1000x, and its not like there's much to screw up there. There is a hose coming out of the compressor side, with the pill in it to a T, which also has a hose coming from the wastegate. The middle of the T goes to a 1/8" coupler, and then off to the boost solenoid.

I keep thinking... maybe my solenoid has gone bad... but why would it suddenly go bad when I replaced the hoses? And if it was bad, I'd imagine it just wouldn't work at all.

I'm stumped, anybody have any ideas?


CN: Boost goes up and down, why?
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Old 06-05-2007, 02:39 AM   #2
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Here is a short data log I did the other day... You can see throttle was constant, while boost was fluctuating (this only shows about 1.5 cycles as there was quite a bit of traffic so I didn't have much room to really get on it).

You can see the wastegate duty is also going with the boost, so its not a boost leak necessarily...

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Old 06-05-2007, 02:43 AM   #3
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Boost goes up and down because in the boost map you are exceeding those values. Its an active system. If it spikes or goes up the ecu will pull it down. The code has to match the pill size and line size. If it does not it will oscilate. Its can be very difficult to learn how to tune this out. It honestly took me several years to be able to do this effeciently. Its one thing to do this on the dyno. Its another thing to have it work right on the road in different temps ect.

Another thing I will tell you is that even though you got the hoses at the dealer there are several restrictor sizes. You dont always get the one you think you are getting. This has stumped me more then once and when measured I realized that cars had the Td04 restrictor on the VF39 or the other way around. If this happens you must get the right restrictor or tune the map. If you have access to your map you can zip it and send it to me and I would be happy to have a look. If its a protune they are locked by the tuner and can only be accessed by them unless they unlock them. However. You can download it with the Open source cable and access it that way. Let me know if there is someway I can help. THis problem can be very frusterating.

Clark
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Old 06-05-2007, 02:46 AM   #4
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When I typed my post and the forum refreshed your second post and graph apeared.

Your problem is:

A. You have the wrong restrictor
or
B. Your tuner did not realize this or made a mistake in the maps.

From the log it is clearly showing you are overshooting the boost targets in the ECUs map. Then you can clearly see the ecu responding by yanking the duty away. Finaly you see the ecu fade back up to the programed duty.

Either get the pill your tuner that you had, have the tuner remap the boost target and duty maps, or send me the file and I will adjust it for you.

Clark
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Old 06-05-2007, 02:47 AM   #5
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I'm working with my tuner and they're being very helpful with it, but thanks anyways!

I would hope the restrictor is the correct size. I got the part number direct from a diagram I got from Jamie (SubaruGenuineParts) for a WRX, so it should be the one for the TD04...

Thanks for the info Clark!
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Old 06-05-2007, 02:48 AM   #6
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Quote:
Originally Posted by AZScoobie View Post
When I typed my post and the forum refreshed your second post and graph apeared.

Your problem is:

A. You have the wrong restrictor
or
B. Your tuner did not realize this or made a mistake in the maps.

From the log it is clearly showing you are overshooting the boost targets in the ECUs map. Then you can clearly see the ecu responding by yanking the duty away. Finaly you see the ecu fade back up to the programed duty.

Either get the pill your tuner that you had, have the tuner remap the boost target and duty maps, or send me the file and I will adjust it for you.

Clark
And then I refreshed, and your second post was there! Thanks again, very good info!
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Old 06-05-2007, 02:52 AM   #7
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IF they cant figure it out have them contact me. I can explain how to fix this.

Clark
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Old 08-13-2007, 01:03 AM   #8
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My car is doing the same up(14-15ish) and down(10) boost dance. I did do the little "3/16" mod, but that was 5 years ago and I have had zero issues untill now. I don't think there are any leaks because when I turn on the MBC, it is rock solid. I have done nothing to the car that should/could affect this, other than a ridiculously hot track day. It is ungodly hot down here. I will take a log tomorrow and see if it looks like the above chart.

I did take the factory ebc apart and it was "gunky", so I cleaned it out. still no change, not even slightly better. I will try to borrow one to see if it fixes it. I'll let you know what happens with that.

FYI, stock turbo, STI TMIC, no tune. I can't imagine that all of a sudden it is compensating for "over boost" as Clark suggests. My car has been untouched for the last 20K miles. Any thoughts?

Last edited by Wheeler Bement; 08-13-2007 at 01:09 AM.
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Old 08-17-2007, 04:20 PM   #9
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Ok, I logged my stuff. Should I be worried if my wastegate duty cycle never goes above 70%? I even have a graph where it goes to 70% and then flat lines for a bit.
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Old 08-17-2007, 06:09 PM   #10
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If your max WGDC map does not allow the WGDC to go past 70% you'll never see numbers higher than that.

As AZScoobie said, it's a tuning issue, not a mechanical one unless the pill has been swapped.

He's right that it's a pain in the ass to sort out, but it can be done.
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Old 08-17-2007, 06:21 PM   #11
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Quote:
Originally Posted by Robertob View Post
As AZScoobie said, it's a tuning issue, not a mechanical one unless the pill has been swapped.
It is NOT necessarily a tuning issue. It very well could be, mine was not. I had the oscillation before getting my tune (on the Cobb OTS map). After the protune, it was still there, nothing changed. Wasn't until I did the solenoid thing that mine went away.
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Old 08-17-2007, 06:48 PM   #12
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THis sounds like a tuning issue to me. If you can email me the maps somehow I would love to just fix it and put this to rest.

Clark
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Old 08-18-2007, 12:35 AM   #13
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Quote:
Originally Posted by Robertob View Post
If your max WGDC map does not allow the WGDC to go past 70% you'll never see numbers higher than that.

As AZScoobie said, it's a tuning issue, not a mechanical one unless the pill has been swapped.

He's right that it's a pain in the ass to sort out, but it can be done.
but my cars ECU is bone stock and I'm just short a tune to go to stage 2. the car has been this way for the last 20K and no issues. today on the way home it appears to have fixed itself. I will have to check tomorrow, as well as all my hoses again just to make sure...but I didn't touch anything to do this.
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Old 08-18-2007, 01:36 AM   #14
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Check the vacuum lines from the t-fitting to the wastegate and compressor. Also, test your boost solenoid by running 12V through it off the battery and spray non-chlorinated brake cleaner through it. I'm having issues or surging and after I did both those things it's now rock solid at 17lbs. I then blew my solenoid right after, but at least I know what the problem was.
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Old 08-18-2007, 02:04 AM   #15
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Sorry my misunderstanding. If it's a bone stock car I don't know what to say - I'd start with checking all the vac lines.
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Old 08-18-2007, 02:41 PM   #16
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I had the same thing for a while, switched to a GM solenoid, got a tune, and boost is rock solid, and no waiver.
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Old 09-23-2007, 06:52 PM   #17
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well, whatever the problem was it went away. I think it was a piece of trash in my Grainger override solenoid. I never bothered to clean it the first time around, but after it fixed itself, I had that though so I checked the lines. they were gunky(oil blowby).
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Old 02-18-2008, 04:50 PM   #18
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So I thought I had fixed this problem. Then lately I've been noticing the car is getting way too much boost, like 21psi. So I tried a low-boost map, should be wastegate boost, no, still 21psi. Crap. So I took the solenoid apart to find the little rubber seal had broken off and was just floating around.

I super glued it back in place, and now I'm back to the oscillating problem.

It only does it sometimes too, which is annoying. Sometimes its perfect, other times it oscillates.
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Old 02-18-2008, 09:11 PM   #19
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I have been having the same problem with my car. I completely replaced all of my vacuum lines and got a pill from the dealer. I now have oscillating boost and I'm overboosting to 20 psi. The best part is that when I take the pill out and replace it with another piece of tubing, I boost .05 MPa (stock gage) and it gradually makes it to .06-.07 MPa (8.7-10.2 psi) at redline when it should only see 8 psi. I think that I'm going to get some drill bits and start playing with the restrictor pill until I get the correct boost for stage 2.
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Old 02-23-2008, 03:15 PM   #20
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Default Oscillation

I was running the cobb vf39 map for a 2.0 wrx and hit boost targets all day long with no fluctuations. I went a couple days ago for a protune. I added a prodrive boost solenoid before they tuned. This was on a dyno which I don't feel was set up correctly no fans for top mount. In third the boost hits target 20psi drops a hair to like 18.5-19psi and sits holding til redline. In fouth however it seems to shoot target of 20 to about 21-22psi then drops to 17psi back to 20psi and so forth until redline. They keep telling me it is mechanical but I never had this problem before. They did the tune in 3rd gear I believe. Plus now I have flutter especially in fourth when this oscillation is occuring. This all seems familiar to your problems. Clark if you see this please send me a tell. I will see if I can get some logs and email them too you.

Thanks a million
-Jason
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Old 02-23-2008, 11:33 PM   #21
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Mine was doing this last year after a track day. Stock turbo, Cobb turbo-back and up-pipe and AP. I was hitting 16-17 steady, then after my track day at WOT I would see it oscillate from 19 to 15, back and forth. I saw a lot of oil and crud on the intercooler hoses, so I replaced them with Samco's and noted that my turbo may be going. The boost problem went away, I think before I even put in the Samco's. Now it's at least 6 months later and now my boost is all out of whack. I have Defi Link gauges and the boost is flicking when I take my foot off the gas. It bounces rapidly. When I go WOT, it oscillates MUCH faster than before and I've recorded 23 psi. Is this even possible on a TD04?? The car feels fine, but does feel like it might be pulling harder as it would with more boost. I saw oil again at the T by the wastegate. I pulled the tube to the gauge sensor thinking maybe it got oil mist in it and was just reading erradically. It looked dry there. I pulled the tube by the pill and found oil.

Has anyone had problems such as these before? Is my turbo letting too much oil by and causing all of my problems? I would love to get a VF34, but not really interested in spending that kind of coin on the car right now. What are cheaper turbo options with standard AP maps? I don't like the idea of farting around with engine management. I just want to drive to work and back. Am I likely going to need a new boost controller if/when I do my turbo since it's seen so much oil?

Thanks for any help.
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Old 02-28-2008, 11:29 AM   #22
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So I ordered a new factory boost solenoid. I found that the one I had, when I blew into it when closed, would still allow a small amount of air through. I figured perfect, thats it. Its leaking, allowing the car to overboost, so its then pulling wastegate duty to lower it, and it causes the oscillation.

I installed the new solenoid last night (tried blowing into it, and I couldn't get ANY air through, so I was pretty excited). Went for a drive, and the problem is still there exactly as it was I'm at a complete loss now.
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Old 02-28-2008, 05:54 PM   #23
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same problem here, I cant seem to hold my full 16 psi anymore. I will floor it and it will hit spike to 19 ish then drop to 5 and below. I cleaned my MAF, replaced all upipe gaskets, boost leak tested.reflashed the ecu.changed out to a new BCS. Im stumped.Still not fixed. I also checked the turbo for shaft play and its fine nothing, although i do hear a funny noise almost like an exhuast leak when driving except louder. i dunno i need help guys. Any input is appreciated.
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Old 02-28-2008, 06:29 PM   #24
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Quote:
Originally Posted by 97subi View Post
same problem here, I cant seem to hold my full 16 psi anymore. I will floor it and it will hit spike to 19 ish then drop to 5 and below. I cleaned my MAF, replaced all upipe gaskets, boost leak tested.reflashed the ecu.changed out to a new BCS. Im stumped.Still not fixed. I also checked the turbo for shaft play and its fine nothing, although i do hear a funny noise almost like an exhuast leak when driving except louder. i dunno i need help guys. Any input is appreciated.
Our problem is similar, but a little different. Mine goes to 19psi, then back down to like 12 then back up, then back down, etc.
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Old 02-28-2008, 07:00 PM   #25
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yea i have no clue man, im gona change the wastegate...
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