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Low boost

Blueballs

Ready to race!
Location
SLC, UT
Anyone experience this ever before, or know what this could be? I have an EQT turbo with 1000 miles on it tuned through Frank Mabo. I’ve been experiencing low boost issues. It won’t boost past 8psi and will drop to about 4-6psi under full throttle. I’ve changed the wastegate with a Mahl wastegate, due to an EPC light throwing a fault wastegate actuator code and after doing some logs and sending them to my tuner, he said my wastegate was bad. I adjusted the new wastegate voltage to 3.56v’s using VCDS. EPC light continues to come on throwing a wastegate actuator code, even with the brand new wastegate installed.

Today I noticed if I put my clutch in all the way, and then push the gas pedal all the way down to rev the car, that the rpm’s wouldn’t rev up, and would just do nothing, but if I half throttle it with the clutch all the way in, it would rev freely. Could this be a faulty DV/BOV (I have the Turbosmart 50/50 recirculating BOV valve)? Could this be a faulty turbo inlet pipe (I have a CTS turbo one which is a little loose due to the screw mounting point being stripped). Could it be bad ignition coils/plugs? Could it be something that went faulty, or a blown fuse, that’s correlated with the accelerator pedal or throttle body? I honestly have no clue. Hoping one of you would know.

Before I had this low boost issue, the car was boosting to its specific psi on the tune, but before it would hit boost, there was major lag. Lag like I’ve never felt before on the car. Almost felt like the engine was under heavy load, but not moving anywhere. My tuner tried to fix the lag with revised tunes, but it still felt very laggy until it hit boost. I then noticed in 6th gear, if I full throttled it, my boost gauge would show 0 boost. The car would not get into boost at all. It was weird, and I knew something was wrong. My tuner asked me to check for shaft play, so I took off the intake hose, turbo inlet pipe, and downpipe, and the turbo felt perfectly fine. No shaft play. I put things back together and ever since then I’ve been having this low boost issue and it won’t boost past 8psi and will drop psi when under full throttle.

I’ve checked and re-checked all boost hoses and intake hoses for leaks/tears/rips and have re-tightened all clamps. I’ve checked the EQT turbo for shaft play. Everything looks and feels good. Please help.


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Diggs24

Autocross Champion
Location
de plains! de plains!
Car(s)
2015 GTI; 2003 Saab
Also just because it reads 3.5 doesnt mean anything. Did it pass adaptation? What position is wastegate flapper when in On position? What is voltage at idle?
 

jerodbroten

Ready to race!
Location
Oahu
Blueballs,
I have an EQT turbo and am having similar issues. I'm being tuned by ED@EQT, yet haven't been able to run my newest revision due to the EPC. Mine is kicking on right when I get to 3,000rpms. I thought maybe my IS38 actuator was going bad because the code is for "Turbocharger module A control". I got it to work briefly set to 3.8, but it didn't last long until I got another EPC. I know exactly the lag you're speaking of. For me, when I went WOT, it was like my car was asking, "you sure you want to go? Absolutely sure? Give you another sec to think about it, answer still yes? Ok, I guess I'll go now...). So because of that, I bought a MAMBA actuator and actually installed it today. Like the IS38 actuator, the new one was set to 3.5 and adaption passed. Did a little prayer and did a test drive. Got passed 3,000rpms and thought "yes, it worked!" only to look down and see that it lit up again. I've adjusted the wastegate so many times on both actuators that I've lost count. Looked at everything I possibly could look at and everything seems legit. No leaks of any sort, nothing touching the actuator, adaption passes from 3.2-3.8 and have adjusted the initial wastegate flapper from just barely touching to holy shit that's tight. Nothing is working for me.
 

jerodbroten

Ready to race!
Location
Oahu
Also just because it reads 3.5 doesnt mean anything. Did it pass adaptation? What position is wastegate flapper when in On position? What is voltage at idle?
To piggy back off this:

Did it pass adaptation?
Yes, mine passes adaption via (ODB11 and COBB AP V3)

What position is wastegate flapper when in On position?
Not sure, but I can take a look tomorrow

What is voltage at idle?
At first, it fluctuates a little, but not much. At 3.55, it might bounce down to 3.50 or up to 3.60, but very briefly and then it will stick to 3.55
 

ACE2

Ready to race!
Location
texas
This kinda makes me worried as I’m buying a eqt turbo and probably buying the wastegate thru them as well already set up to go. Hoping someone finds a solution so I’m not stuck in this scenario


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Hoon

Autocross Champion
Location
Rhode Island
I'd start with a boost leak test and go from there. Verify that the wastegate is shut and not leaking also.
 

MadMen

Ready to race!
Location
Mooresville, NC
Do you guys have the 'Direct Acceleration' tweak done on your cars? If yes, try setting it back to the stock setting of 'incremental over time' or whatever it is. This seemed to cure my EPC woes (knocking on wood), along with smoothing out the part throttle shifting.
 

Diggs24

Autocross Champion
Location
de plains! de plains!
Car(s)
2015 GTI; 2003 Saab
Verify that the wastegate is shut and not leaking also.
How can you do this? Voltage just says "Hey I'm applying this voltage" but won't give any info on whether it's shut or not.

hmmm, I wonder if having vcds/obd11 test the end stops of the wastegate has any effect? Like "Here is lower and here is upper voltage"?
 

Hoon

Autocross Champion
Location
Rhode Island
How can you do this? Voltage just says "Hey I'm applying this voltage" but won't give any info on whether it's shut or not.

hmmm, I wonder if having vcds/obd11 test the end stops of the wastegate has any effect? Like "Here is lower and here is upper voltage"?
I'd pop the DP off the turbine housing and start the car.
 

Blueballs

Ready to race!
Location
SLC, UT
Also just because it reads 3.5 doesnt mean anything. Did it pass adaptation? What position is wastegate flapper when in On position? What is voltage at idle?


Yes it passed adaptation.

I’ll check the voltage at idle and position of wastegate flapper when I’m On position. I posted logs if you could check those out. In meantime this is the code I keep getting:





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