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Old 09-09-2020, 05:56 AM   #1
AfroSlyStone
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Question Low boost on 92 740 turbo

Hello all I have been trying to find a solution to this problem. I have posted on Facebook and discord and got suggestions but no good outcome. I was told that I have a vacuum leak basked on the video people. My speedo doesn't work so I am going by rpm. I did a pressure test and a fuel injector o ring was bad so I replaced it but still the same outcome. Does anyone have any other suggestion?

Here is a link to the video
https://photos.app.goo.gl/CjCS7LnpLoSDffQs7
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Old 09-09-2020, 08:24 AM   #2
Janspeed
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i watched your vid and your turbo does seem to create boost. When you let go of the gas pedal you can hear the CBV dump the boost. If the car has no aftermarket boost controler then it all seems pretty normal to me.

Maybe spool-up could be a bit better? You could try to dial in some more pre-load on the wastegate actuator rod. That way boost will build a bit faster.
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Old 09-09-2020, 09:14 AM   #3
AfroSlyStone
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I do have a boost controller
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Old 09-09-2020, 10:12 AM   #4
iHateVolvoPeople
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Quote:
Originally Posted by AfroSlyStone View Post
I do have a boost controller
I wasn't able to load your video, but assuming you don't have boost leaks and your wastegate puck isn't leaking, then you likely have a bad turbo. We went through 2 'known good' 13c turbos on my buddy's 245+T. Both took forever to spool and I was almost positive his car had underlying issues.

Then we found a NOS 13c turbo for $300 and it fixed all our problems.
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Old 09-09-2020, 12:29 PM   #5
ZVOLV
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I bet cracked turbine housing. Take off the downpipe and look in there with a mirror.
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Old 09-09-2020, 12:42 PM   #6
iHateVolvoPeople
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I bet cracked turbine housing. Take off the downpipe and look in there with a mirror.
Ah yes, this too. Though I would think the crack would need to be a significant size to make a difference, as I've run a handful of cracked turbos without issue.
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Old 09-09-2020, 02:11 PM   #7
Fa182
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The vacuum on the boost gauge in idle seems quite low from what I can tell?
The needle is much more to the left on mine - I have a numerical boost gauge on mine as well and it shows about 0.65 during idle and 0.85bar vacuum during cruise (if I remember correctly).
Are you sure you don't have any vacuum or boost leaks?

Under boost it doesn't seem to be far off than what it should be I guess?
The stock boost pressure is 0,55bar (I think - about 8psi) and by the looks of the gauge it seems to be there +/- I'd say.

Last time I saw a post from you on the Facebook group the wastegate actuator was disconnected or something, is everything alright on that end?
As said above, does the actuator arm have enough preload? Without any preload on it, the wastegate flapper thing inside the turbo isn't fully closed and is creating a boost leak.
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Old 09-10-2020, 01:30 PM   #8
AfroSlyStone
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The Facebook group the wastegate actuator was disconnected or something, is everything alright on that end?
As said above, does the actuator arm have enough preload? Without any preload on it, the wastegate flapper thing inside the turbo isn't fully closed and is creating a boost leak.
The wastegate actuator is on. How can I check the preload? I will check the wastegate flapper to see if it isn't fully closed. I have to ask but can you tell me what the wastgate flapper is?
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Old 09-10-2020, 01:49 PM   #9
ZVOLV
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Take the downpipe off. Inspect for a MELTED turbine housing near the flapper/puck inside there.
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Old 09-10-2020, 02:15 PM   #10
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Quote:
Originally Posted by AfroSlyStone View Post
The wastegate actuator is on. How can I check the preload? I will check the wastegate flapper to see if it isn't fully closed. I have to ask but can you tell me what the wastgate flapper is?
Here is a picture of the wastegate flapper.
https://images.app.goo.gl/ofgMTJpCJhWnjYJs7
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Old 09-10-2020, 04:17 PM   #11
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Quote:
Originally Posted by AfroSlyStone View Post
How can I check the preload?
You just make sure the flapper is closed and then connect the actuator arm by pulling it out a little bit from the actuator housing.
The preload needs to be just enough so that the flap is staying closed. The arm has a thread on it on the front part where it connects so you can adjust the preload.
If it's too loose, turn the front part clockwise so the whole arm gets shorter.

Basically just like shown here:
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Old 09-10-2020, 07:01 PM   #12
dl242gt
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A clogged converter can reduce boost response and performance.
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