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Old 10-31-2017, 02:25 PM   #1 (permalink)
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How do I test a waste gate on a turbo?

Need help for the turbo experts. Upgraded the downpipe and bumped up the tune on my gti. I am having a huge surge problem. For example in 2nd gear as it builds boost it suddenly loses the boost momentarily then suddenly bites hard. It makes it undrivable as you get thrown back in your seat, then lurch forward, then thrown back again.

I suspected a boost leak so I did a pressure test. Everything looked good. I now suspect a failing waste gate (won't stay closed under boost). Does this symptom fit a bad waste gate and how to I check it properly?

2005 VW GTI
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5 Speed
Spikes 21 pounds of boost and runs 18-20

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Old 10-31-2017, 08:53 PM   #2 (permalink)
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Check the vacuum line going to the wastegate actuator. If it is cut or leaking it could cause inconsistent boost or overboost.

Edit: Could also be the tune. I had a similar problem recently that caused an idle issue but reverting to a previous tune cleared it. Maybe try reflashing back to a previous setup and see if it goes away.

Not really sure of an easy way to test the wastegate without just taking it apart and looking for something that is toast.
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Old 10-31-2017, 11:38 PM   #3 (permalink)
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Originally Posted by No Have MSG View Post
Check the vacuum line going to the wastegate actuator. If it is cut or leaking it could cause inconsistent boost or overboost.

Edit: Could also be the tune. I had a similar problem recently that caused an idle issue but reverting to a previous tune cleared it. Maybe try reflashing back to a previous setup and see if it goes away.

Not really sure of an easy way to test the wastegate without just taking it apart and looking for something that is toast.
You know it's funny that you say it might be the tune because I was thinking that might be what it felt like. It's almost like the throttle cuts out

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Old 11-01-2017, 12:20 PM   #4 (permalink)
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Is this the same boost level you ran before? If you drive it easy and don't get the boost up too high does the issue go away? If you ease into it in second and run it up to RL is there a point you see it consistently cuts out? I am assuming you are maf tuned and not speed density. If you have Upgraded the boost you may have gotten to the point your maf can't read it.
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Old 11-01-2017, 12:35 PM   #5 (permalink)
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I would have thought a fuel cut if it is a hard lurch.

Do you have the ability to monitor your injector duty cycle?

Another thought, do you have appropriate spark plugs and gap for this level of boost?
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Old 11-01-2017, 02:49 PM   #6 (permalink)
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If its a VW from the mid 90's to the mid 2000's I could randomly guess coil packs and probably be right. If it misses then dumps raw gas past the turbo it's going to have a similar effect, but you'll hear a distinct popping sound.

Do you have a boost guage hooked up that's telling you it's losing boost or do you just feel/hear it?

Generally a waste gate or bad bypass valve isn't going to shudder like that, it just won't hold boost past a certain low psi. But it could be possible on the waste gate side.

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Old 11-02-2017, 05:52 PM   #7 (permalink)
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Originally Posted by theangrydragon View Post
If its a VW from the mid 90's to the mid 2000's I could randomly guess coil packs and probably be right. If it misses then dumps raw gas past the turbo it's going to have a similar effect, but you'll hear a distinct popping sound.

Do you have a boost guage hooked up that's telling you it's losing boost or do you just feel/hear it?

Generally a waste gate or bad bypass valve isn't going to shudder like that, it just won't hold boost past a certain low psi. But it could be possible on the waste gate side.
Yes I have a boost gauge and can see it cut. I have properly gapped and heat ranged plugs.

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Old 11-02-2017, 05:54 PM   #8 (permalink)
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Originally Posted by No Have MSG View Post
Is this the same boost level you ran before? If you drive it easy and don't get the boost up too high does the issue go away? If you ease into it in second and run it up to RL is there a point you see it consistently cuts out? I am assuming you are maf tuned and not speed density. If you have Upgraded the boost you may have gotten to the point your maf can't read it.
If I ease into it it will not do the surge. 2nd gear is where I feel it most, 3rd and 4th too. If I'm going slow and put it in 3rd gear and floor it I can watch the boost build slowly (wrong gear for speed) until it hits around 20 without surging.

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Old 11-03-2017, 08:54 AM   #9 (permalink)
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Yeah it is just kind of hard to say without being there. It sounds like fuel cut from overboost but even if you are set at 18psi, a short duration spike at 21 is not that severe that it should fuel cut that hard.

Without knowing that car well it almost sounds like you are kind of at the limit of the factory parts. I quick search says that they are 7-8psi stock. I wonder if you are at the point that the factory wastegate actuator is at it's outer limit of what it can handle. It might need ported to handle the boost levels you are running.

Am kind of impressed that guys say that motor will handle upwards of 23psi stock. That's pretty good.
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Old 11-03-2017, 09:36 AM   #10 (permalink)
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Originally Posted by No Have MSG View Post
Yeah it is just kind of hard to say without being there. It sounds like fuel cut from overboost but even if you are set at 18psi, a short duration spike at 21 is not that severe that it should fuel cut that hard.

Without knowing that car well it almost sounds like you are kind of at the limit of the factory parts. I quick search says that they are 7-8psi stock. I wonder if you are at the point that the factory wastegate actuator is at it's outer limit of what it can handle. It might need ported to handle the boost levels you are running.

Am kind of impressed that guys say that motor will handle upwards of 23psi stock. That's pretty good.
Yeah the boost level should be fine for the car. Many many people run the exact setup. Unitronic is a very popular tune and the down pipe is 42dd which is a major brand. I put the right plugs, and even upgraded coil packs in and still nothing. Maybe I'll pull the turbo and look at it

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