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Normal Boost few seconds then drops?

XuperXero

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#1
Having the most peculiar problem since I got my car back from head gasket swap.

Car is normal in the first few seconds of getting on throttle hitting 20~21 psi, after a few seconds it drops to 11~10psi. Drive normally then get on it again and the same thing happens. If I'm always on the gas without normal driving, it's always 11-9 psi. Does not seem to be affected by rpm. As long as it takes a break, it'll go back to full boost.

It feels like as if something heated up during higher boost causing lost in boost pressure and goes back to normal when it cools. Checked all clamps, they're tight... Any clue?
 


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#4
Mine does the same thing no matter the rpm. Even at part throttle, say 2psi, and then it'll drop down to 0 or into vacuum.

Sent from my Nexus 6P using Tapatalk
 


OP
XuperXero

XuperXero

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Thread Starter #5
Did a throttle and idle learn reset, cleared all cam learned positions and throttle positions. Problem still persists. I forgot to mention that I'm also getting fluctuating idle.
 


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#6
Isn't that just overboost kicking in? I could be wrong, but isn't it like 10 seconds of full boost or something then it drops off?
 


OP
XuperXero

XuperXero

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Thread Starter #7
Just checked diverter valve and all the vacuum lines yesterday. All nice and snug. Tightened down all the intercooler hose clamps just for precaution. Issue still persists...

Driven hard, the car will only boost to 10psi. Anybody got any ideas? Getting tired of GTI's smoking me.
 


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#8
Did you actually remove the bumper to check the boost hoses connected at the intercooler? Mine completely came off the hotside, looked as if it was connected. Next day took the bumper off and guess what... The stock silicone was sitting basically lip to lip.

Sent from my XT1650 using Tapatalk
 


Sekred

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#9
Strange how this problem started after removing/replacing cylinder head and gasket. Have you anyway of running a data log to look at WGDC and throttle angle?
 


OP
XuperXero

XuperXero

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Thread Starter #10
Did you actually remove the bumper to check the boost hoses connected at the intercooler? Mine completely came off the hotside, looked as if it was connected. Next day took the bumper off and guess what... The stock silicone was sitting basically lip to lip.

Sent from my XT1650 using Tapatalk
No, I yanked and twisted it as hard as I could under the car, didn't budge.

Strange how this problem started after removing/replacing cylinder head and gasket. Have you anyway of running a data log to look at WGDC and throttle angle?
Here's a Vdyno from before and after comparison. 174hp vs 228hp. You can see boost curve differences between the two.


Here's datazap of my logs... I have no idea if it's a mechanical issue or the ECU is limiting the boost? WGDC seems to be different.
https://datazap.me/u/xuperxero/revo-stage-1?log=0&data=10-13 - Good condition
https://datazap.me/u/xuperxero/low-boost-issue?log=0&data=7-12 - low boost condition
 


Sekred

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#11
Looking at the two Datazaps, the lower boost on the second graph also shows lower duty cycle. It looks like it may be ECU related. The first graph shows about 16 lbs @ 6000 rpm, 94% duty cycle, the second graph shows 10 lbs @ 6000 rpm, 54% duty cycle. The second Datazap almost looks like what you might see with a stock tune and boost restriction in 2nd gear. Sure the dealer did not do a sneaky re-flash when they did the head gasket?.

Just looking again at that 2nd datazap and your manifold vacuum looks very low too when your off the throttle, that's strange. Maybe its sucking air/ pushing boost there.
Hows the intake hose between the air filter and turbo?, sucking air pass the MAF causes all kinds of unusual problems. You need to look at everything the dealer has touched when they change out the cyl head.
 


OP
XuperXero

XuperXero

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Thread Starter #12
Long story short: I went for engine swap first with a short block, but motor was a dud and then decided to do head gasket swap on original motor. So all the parts have been swapped on twice... So it could be anything. I have no methods for doing a leak test either.

If they did do the reflash, then how am I still hitting 24 psi? Also, boost level across the board is below stock tune. It feels slower than stock.

Intake tube from filter leading to turbo looks good. The cross pipe is still stock with mountune intake hose.
 


Quisp

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#13
Just checked diverter valve and all the vacuum lines yesterday. All nice and snug. Tightened down all the intercooler hose clamps just for precaution. Issue still persists...

Driven hard, the car will only boost to 10psi. Anybody got any ideas? Getting tired of GTI's smoking me.
Stock diverter? Mine was tight and all but o ring on tip was gone ( DV+). Never got over 16lbs.
 


Sekred

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#14
Long story short: I went for engine swap first with a short block, but motor was a dud and then decided to do head gasket swap on original motor. So all the parts have been swapped on twice... So it could be anything. I have no methods for doing a leak test either.

If they did do the reflash, then how am I still hitting 24 psi? Also, boost level across the board is below stock tune. It feels slower than stock.

Intake tube from filter leading to turbo looks good. The cross pipe is still stock with mountune intake hose.
I don't really think you have a boost leak because your hitting 24psi (briefly) and then it falls away. I would still check the DV as Quisp suggested though, it maybe popping open.

Go back to the basics and clean your MAF sensor, check your plugs, measure IM vacuum at idle. Any CELS?. Can you reflash back to the stock tune?. I don't believe in coincidence so it is probably something the dealer techs have done. Something left in the intake system, don't laugh I have seen anything from rags to plastic left jammed in the intake system.
 


Last edited:
OP
XuperXero

XuperXero

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Thread Starter #15
Stock diverter? Mine was tight and all but o ring on tip was gone ( DV+). Never got over 16lbs.
I don't think the diverter valve was ever taken off the turbo.

I don't really think you have a boost leak because your hitting 24psi (briefly) and then it falls away. I would still check the DV as Quisp suggested though, it maybe popping open.

Go back to the basics and clean your MAF sensor, check your plugs, measure IM vacuum at idle. Any CELS?. Can you reflash back to the stock tune?. I don't believe in coincidence so it is probably something the dealer techs have done. Something left in the intake system, don't laugh I have seen anything from rags to plastic left jammed in the intake system.
How does one check the operation of the DV? Boost solenoid is still clicking and whirring at shut down, so I'm assuming it works. The forged BOV adapter is still there making the bov noises on lift off. But I'm now concerned if the vacuum lines on it are correctly connected, anybody have a picture or diagram on which nipples the vacuum lines connect to?

I've already checked the MAFS, plugs are new after the gasket swap. I've taken off intake hoses and checked inside no issues (with exception of checking inside intercooler). I have the RevoSelect so yes, I can choose stock, 95 octane and 98 octane. I'll give a shot at stock tune today. Keep the ideas coming!
 


Sekred

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#16
To check the DV you would need to remove it from the turbo and inspect any O rings and seals. Remove the Forge adaptor and check the seals on that at the same time. The OEM DV is control by the ECU and connected electrically, no vacuum lines.
Check the hoses on the boost solenoid at the same time.

KP 39 Wastegate Plumbing.jpg
 


OP
XuperXero

XuperXero

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Thread Starter #17
Stock diverter? Mine was tight and all but o ring on tip was gone ( DV+). Never got over 16lbs.
I don't really think you have a boost leak because your hitting 24psi (briefly) and then it falls away. I would still check the DV as Quisp suggested though, it maybe popping open.

Go back to the basics and clean your MAF sensor, check your plugs, measure IM vacuum at idle. Any CELS?. Can you reflash back to the stock tune?. I don't believe in coincidence so it is probably something the dealer techs have done. Something left in the intake system, don't laugh I have seen anything from rags to plastic left jammed in the intake system.
To check the DV you would need to remove it from the turbo and inspect any O rings and seals. Remove the Forge adaptor and check the seals on that at the same time. The OEM DV is control by the ECU and connected electrically, no vacuum lines.
Check the hoses on the boost solenoid at the same time.

View attachment 15722
Yes I meant the hoses on the solenoid. I felt them and I couldn't make sense of the routing. That pic is perfect. Thanks!

FYI Problem persists on stock tune and also today is 10 degrees C cooler than yesterday at 20C. Boost holds longer and recovers faster than yesterday. So it seems temperature related. Something overheating and causing boost drop.

But will need to find time to check the hoses and DV first.
 


OP
XuperXero

XuperXero

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Thread Starter #18
DV and Wastegate checked by mechanic. No problems. Hoses are lined up too according to picture.

Getting sick of this... Actually debating if I should get rid of this car.
 


OP
XuperXero

XuperXero

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Thread Starter #19
Boost solenoid changed at suggestion of mechanic. Issue still persists.

But new observations:
1. Cold starts. During warm up, it used to gently drop from 1500 to 1100. Now it drops sharply below that and will shake the whole car before going back up again to 1100.
2. Commanded and Actual AFR are completely off from each other in most cases. I don't recall it behaving in such way in the past.

Any tuner have a look at my logs and point me in the right direction? [MENTION=4300]Alex@Stratified[/MENTION] [MENTION=3805]Tune+[/MENTION] [MENTION=930]dyn085[/MENTION] @razerlab [MENTION=688]Sourskittle[/MENTION]s or anyone else? I'll paypal you coupe of beers for pointing in the right direction.

https://datazap.me/u/xuperxero/revo-...g=0&data=10-13 - Good condition
https://datazap.me/u/xuperxero/low-b...og=0&data=7-12 - low boost

Getting very desperate here...
 


OP
XuperXero

XuperXero

Active member
Messages
587
Likes
124
Location
Wuxi
Thread Starter #20
Boost solenoid changed at suggestion of mechanic. Issue still persists.

But new observations:
1. Cold starts. During warm up, it used to gently drop from 1500 to 1100. Now it drops sharply below that and will shake the whole car before going back up again to 1100.
2. Commanded and Actual AFR are completely off from each other in most cases. I don't recall it behaving in such way in the past.

Any tuner have a look at my logs and point me in the right direction? [MENTION=4300]Alex@Stratified[/MENTION] [MENTION=3805]Tune+[/MENTION] [MENTION=930]dyn085[/MENTION] @razerlab [MENTION=688]Sourskittle[/MENTION]s or anyone else? I'll paypal you coupe of beers for pointing in the right direction.

https://datazap.me/u/xuperxero/revo-...g=0&data=10-13 - Good condition
https://datazap.me/u/xuperxero/low-b...og=0&data=7-12 - low boost

Getting very desperate here...
 




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