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Old 07-20-2007, 07:51 AM   #1 (permalink)
The Flying Dutchman

 
Join Date: Oct 2006
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Not holding boost; Bad T25 wastegate?

Hi guys,

I found some topics on this forum that came close, but I would like some 2nd opinions:

I have a stock U12 bb det with 3" exhaust, JWT ECU and a Turbosmart MBC set to 10/11 psi. Drove it for some weeks with a big smile on my face

But last week suddenly the boost was spiking to this set 11 psi and then dropped till about 7 (stock psi setting right?!). I did a preasure test from intake all the way down, then fixed some leaks but the problem is still there. Then I replaced my MBC with one I know for sure thats working... Still the same problem.

Vacuum lines are still on the same place as before and checked for leaks...None.

So:
No leaks (IC and vacuum)
MBC is ok

Did my (crappy T25 as said on this forum) wastegate die on me? or can there be another problem?

Thanx guys,

Daniel
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Old 07-20-2007, 08:21 AM   #2 (permalink)
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questions,

1. did the boost controller spike to anything when it was set at 11 psi previously, or did it stay at 11psi all the way through the band? If it spiked before higher than 11, you probably just need to play with the settings again.

2. Now that it spikes and falls off, what rpm does it spike at, what rpm's is it trailing off? I'm willing to bet it hits at 4k and trails to 7psi after 5.5-7k or so.

See if you can drive it w/o the mbc in series and see what the boost gauge does. (or turn it all the way down)... if it drifts below stock boost then you know your wastgate is the culprit.

Seems to me its more likely the mbc... they tend to spike, peak at full boost (3.5-4.5k) and slowly drift back down at higher rpm. And you were probably enjoying yourself so much you concentrated on keeping your hands on the wheel rather than stare at the boost gauge to notice until now .

I think that weather can affect it a little bit as well... from what I've seen, but I'm not Confusious.
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Last edited by XxToKeSxX; 07-20-2007 at 08:24 AM.
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Old 07-20-2007, 09:08 AM   #3 (permalink)
The Flying Dutchman

 
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1.I setted the MBC to 11 psi. So it spiked to about 13/14 psi and then dropped till 11 psi and stayed there pretty steady.
2.When the problem began, the boost still spiked to 13/14 psi but dropped to 7 psi. I turned off the MBC and it ran stock boost (7 psi).
3.I changed my MBC for another one but the problem is still the same, so I donít think the MBC is the problem ?

So short: With MBC off I run 6/7 psi. With MBC on it spikes to about 13 psi and then drops to the same 6/7 psi.

Havenít checked the exact RPMís
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Old 07-20-2007, 09:27 AM   #4 (permalink)
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Since you have access to a pressure tester try this... hook up compressed air to a gauge, to the wastegate actuator line with your car off... listen for sounds and watch the pressure.

If it drops you either have a leak in the line, or the diaphram on your actuator might be chalked.

If the arm moves w/ no problems and no leaking, then it has to be either the mbc or the wastegate is cracked.

If the line takes more pressure than normal and then pops open, then there is something causing the wastegate to stick.


Lastly, what gear are setting your mbc? I did mine in 4th gear...

Hopefully someone else can chip in because I don't know a lot about these things, just trying to put my head to use... it would seem to me that if its holding stock boost then its alright. I only usually hear from people having problems with the stock wastegate when they set it higher like 17 and 18 psi or so...

Last edited by XxToKeSxX; 07-20-2007 at 09:30 AM.
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Old 07-20-2007, 09:36 AM   #5 (permalink)
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Definitely pressure test the IC piping. That would be my first suggestion. With running higher psi you could have unknowingly caused a leak.

As for the wastegate going bad I highly doubt that is the case. Those thing will last forever really. Your probably looking at a boost leak (check the bov if you haven't already) or the turbo is sh*tting the bed on you.

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Old 07-20-2007, 12:01 PM   #6 (permalink)
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The wastegate springs get soft in them over time, i had the same problem. So i did the same as a fellow old timer MI member did. Went to home depot and got a spring, tested it, held roughly 10psi of boost untill it started to move and just put it on the end of the WG rod and the wastegate itself, issue solved! Ran 13-14psi steady without any fluctuation.
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Old 07-20-2007, 12:19 PM   #7 (permalink)
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I had a similar problem way back. I thought the same as you, but when really it was my bov. My bov was never really closing thus the boost I made was recirculating all the time. It would spike and then come crashing down over and over. Anyway, just something to check.

I had a vaccum line going to bov that I shouldnt have. That was my fix.
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Old 07-22-2007, 05:35 PM   #8 (permalink)
The Flying Dutchman

 
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Checked the BOV today and works fine.
Gonna check the wastegate this week. If its bad, i have 2 choices:

1. Getting new wastegate
2. ... spend some more bucks and get a T28 turbo

Anyway, thanx for the response guys. We're gonna do some checks this week
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