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Old 11-16-2003, 01:04 PM   #1
O2-GGA
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Default Boost surging in 5th

I have a stealthback tbe. I've had it on for 2 weeks. Now while on the highway in 5th gear I get surging at WOT. If I'm cruising @ 3,000rpms and WOT, it's boosts for a second than stops, boosts than stops and so on. Before that happened I did tighten the acutator to get rid of wastegate flutter(2 1/2 turns). Should I loosen it back to stock??




Steve
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Old 11-16-2003, 07:06 PM   #2
BlackEye
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Default Hmmm ....

I have seen the same thing with either trying to run the restrictor or do the wastegate actuator mod (I have done both) to my COBB stage 2.

Yes, IMHO it is the actuator mod, I had mine set at two turns shorter and had the same type of yoyo boost occasionally. I turned it back a half a turn and it RARELY happens now.

I would lengthen your actuator like 1 full turn. That will get you back to 1.5 turns.

They way I understand it both the restrictor and the wastegate preload inhibit the responce time of the factory wastegate actuation. When you come on boost quickly in high load situations the wastegate does bleed the boost off quick enough, then prolly the computer cuts it back, then it attempts to let it build again. The same thing often starts happening, boost gauge starts looking like a yoyo.

A small test that might help diagnose...

Try gently comming to full boost and if it does not do the yoyo deal then yeah it is the actuator... (IMHO)

Russ
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Old 11-17-2003, 08:39 PM   #3
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I did lengthen the actuator one full turn(on Saturday) and still getting it. I just did the 3/16th mod uninstall today. I think that had something to with it also. I'll tell you if that worked.
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Old 11-18-2003, 10:28 AM   #4
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A bit off topic but wot in 5th is about the best thing i can think of to bring on knock.

If you have a boost gauge, ,my guess is that you are overshooting target by an arse-load and the stock ebc is yanking boost for a moment, giving it back and when it over shoots again it yanks again.

But like i was saying....5th is no gear for the heavy foot. Downshift.
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Old 11-18-2003, 11:17 AM   #5
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Default What....

I run full boost in fifth all the time, I motor at like 90-95 all the way to work every morning and I have never had any issues.

I could see maybe a concern if you run a MBC or something that will not accomodate much change but with a full OBDII working for you, I think your safe. IMHO (don't take this wrong but where did you here that)

Is it because of the inefficientcy of the scoop at speed, I heard stuff about that a while back. (I run an STI)

Anyway, I love to torque around in fifth all day long...I can out excellerate most cars with out downshifting, fifth has balls....

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Old 11-18-2003, 11:58 AM   #6
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my car does the same thing in every gear though.i have fully catless stage 2 with the greddy e-01 boost controller and it surges bad.i thought the bov was leaking so i shimmed it and still does the same thing.i havent messed with the actuater i will try that this weekend.i dont drive the car during the week.weekend warrior
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Old 11-18-2003, 12:18 PM   #7
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Default Re: What....

Quote:
Originally posted by BlackEye
I run full boost in fifth all the time, I motor at like 90-95 all the way to work every morning and I have never had any issues.

What do yo mean "full boost" ?

I usually cruise at 80mph to work (30 miles each way) and I'm in vacuum 90% of the time.
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Old 11-18-2003, 04:09 PM   #8
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Quote:
Originally posted by shields102
A bit off topic but wot in 5th is about the best thing i can think of to bring on knock.

If you have a boost gauge, ,my guess is that you are overshooting target by an arse-load and the stock ebc is yanking boost for a moment, giving it back and when it over shoots again it yanks again.
That's exactly how it feels. I was just testing it out on the highway. I wasn't racing anyone, just wanted to see how it pulled in 5th. It does it alittle in 4th too
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Old 11-18-2003, 11:20 PM   #9
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Is it best to set boost in third or fourth gear? I tried a search but turned up only minimal info. Also, should I avoid setting boost during high humidity?

The last time I set my "hi. boost" (which was a while ago) I think I did it third gear.

Oh yeah, I am setting boost with a Profec-B (spec 1).
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Old 11-19-2003, 12:25 PM   #10
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5th is an overdriven crusing gear. It puts a ton of load on the engine vs. lower acceleration gears......thats one reason why larger turbos have lower boost thresholds in higher gears...there is that much more load.

And as far as having functional obd-2 on your side....try asking all of those folks with #4 ring failures what obd-2 did for them....that happens without a check engine light most of the time.
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Old 11-19-2003, 06:53 PM   #11
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Default 5th question...

Quote:
What do yo mean "full boost" ?

I usually cruise at 80mph to work (30 miles each way) and I'm in vacuum 90% of the time.
If I am just cruising yes, you would be correct. In actuality though I am seeing like 2-5psi of boost most of the time on the freeway. That is because of constant passing.

What I meant by full boost is PTFB I pass almost continually at o'dark thirty... in the morning when I go into work. During my passing I almost alway hit like 1 + bar boost and the engine just seems to love it. On the dyno I was putting down 220 + fttq to the wheels from 3K rpm all the way to about 5300 rpm with a peak of 230. It is the torque that I love so much about this car. Exceleration is effortless.

Anyway, I understand what is being said about load, but what about wear? I don't really think you are applying to much load with a factory turbo set at 15.8 psi, run at 3K at PTFB. I do believe however that you are applying more wear at higher rpm.

But I think this is splitting hairs.... I really do both, It just sounded like it was being said that driving around at 3k pushing 1 bar +- was damaging the engine. IMHO I don't think so...But inform me if I am wrong before I do real damage please...

"If there is one thing I know it is that I know nothing"

BlackEye...
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Old 11-19-2003, 07:33 PM   #12
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The 3/16" mod and TBE don't mix well with the stock ECU. I suggest putting the stock restrictor back in, shortening the wastegate actuator just enough to get rid of most of the flutter, and THEN reset the ECU. It will take the ECU a day or two to learn to boost properly but it really smooths out. I did this with my catless stealthback and now the stock ECU boosts just fine.

-- Ed
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Old 04-07-2004, 04:04 PM   #13
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needed to bring this post back to life.

i need to find out if i should lengthen the acutator or shorten it to help out with this ghey surging? if so how many turns
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