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Old 09-07-2019, 01:39 PM   #1
thelostartof
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Default Lower than Expected boost External WG

My 744 has a Tial MV-S that I have been running for 6+ years, unit was new when installed and has been flawless eversince I put it on. I am running a Greddy Profec B Spec EBC that has also been flawless for even longer.

So as of last week all of a sudden my peak boost dropped for each setting, the EBC has High, Low and off which give me 3 boost settings. The Off settings which went off WG spring was running around 11psi and is now at 8psi, low was 16psi and is now 13psi, High was 26psi and is now 21psi. This issue came on very sudden, I was out on a tuning drive to get more e85 and things were going great at 26psi until about 20 min into the drive when i left a stoplight and noticed that the boost was all of a sudden lower and the power just wasnt there.

I have swapped out the Greddy unit for another known working unit along with a combination of control unit and soleniod and both units produce the same results of boost.

I have pressure tested the car pre-turbo to 30psi and found no boost leaks, none of the WG hoses or lines leak, nothing at the intake manifold or any place else. So because of this I am fairly sure that there are no boost leaks.

That leaves me to think the issue has to be the WG, being that the External unit Dumps to atomosphere everything sounds 100% normal, the peak boost is just lower.

So any idea's of what I should check next? This engine has around 1500 miles on it since I rebuilt it and otherwise everything has been perfect including boost control up until last week when all of a sudden I lost a bit of power and boost.

Thank you for the time to read and any help you can offer, the car has been running great and I wanted to finally take it back to the strip to finally go for proper 11's on MS but with this boost control issue it makes it harder to tune without boost being where it should be.

Mike
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Old 09-07-2019, 03:02 PM   #2
RvolvoR
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check the fire ring on the bottom of the gate, check the valve itself to make sure it isnt sticking partially open, swap in a known good spring.
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Old 09-07-2019, 04:31 PM   #3
JohnLane
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Mike measure pressure required to get the WG off of it's seat.

May be related to the spring.

If boost threshold is same as before the WG is not leaking badly.
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Old 09-07-2019, 07:42 PM   #4
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I tested my gate with an air compressor, regulator, manual boost control and apparently every adapter fitting I could find in the tool box

https://youtu.be/l-UmC6YKimE
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Old 09-08-2019, 12:04 AM   #5
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I know this will sound stupid, but voice of experience here and from Doug as well. Are you sure your gauge didn't go haywire?
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Old 09-08-2019, 01:07 AM   #6
thelostartof
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Boost guage is not just reading low, the lack of the extra 5psi on that holset is very very noticable (something like 50+whp), nevermind that the dash guage also shows the drop in boost. Oh I should mention that the MS datalog also shows the lack of boost also. This is how I validated when it went wrong on the test drive as I happened to be datalogging at the time.
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Old 09-08-2019, 10:25 AM   #7
VB242
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Exhaust leak at the manifold-head?
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Old 09-08-2019, 02:01 PM   #8
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Check your turbine wheel & compressor wheel for damage...
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Old 09-09-2019, 07:41 AM   #9
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If it does the same thing with multiple gates I would suspect a boost leak or exhaust leak causing the turbo to not build boost like it should.
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