Slight overboosting problem

88BB8B · Jul 16, 2018

I did some serching, but coildn't quite find what I was looking for.
My 1997 Talon TSI has the supporting mods to turn the boost up just a bit (was running 15psi when I very first got it) blew up the shitty trans that was in it, and it sat for a while, after getting the new trans in, it was boosting to only 13-14 pair, which I wasn't ecstatic about, but at least it's not very harmful. As I've driven boost slowly went up, until last night it was boosting perfectly to 15 pain, then holding. This morning, I find particularly in second gear, it's boosting to 17, and kissing 18psi. But in 3rd or higher it only boostzs to 15.

I have an HKS electronic boost controller, and stock wastegate and everything. I'm wondering if anybody can tell my why it might be overboosting, furthermore, is 17psi on the stock fuel system, stock T28, and 3" exhaust definitely harmful. Would it be obvious to me driving if it were knocking?

My wastegate actuator is only bolted on to the turbo with one bolt, could it just be pivoting on the bolt, and thereby causing the boost pressure to change?

pauleyman · Jul 16, 2018

Fix the bolt. Stock turbo is not t28 so what do you have?

pauleyman · Jul 16, 2018

You've also been a member for several years and have no profile. How can we help you if we dont know what you have?

88BB8B · Jul 16, 2018

Alright, I'll fix that. And I meant to say t25. I Joined about 2 years ago when I got the car. Blew the tranny within a few hours of driving, car sat since then until a couple weeks ago when I got a new trans, been needing a bit of help as I iron out the smaller problems this car has.

But anyway, I was messing around with the car today, and it only overboosts if boost is built too quickly. If I build boost slowly by starting in 3rd or 4th from low rpm, or roll on slowly at hgher rpm, the boost holds at 15 psi, and doesnt go past. It's as if my wastegate is laggy, does it need to be lubricated? Or adjusted? What is this behavior usually a symptom of?

pauleyman · Jul 17, 2018

It's a symptom of too large exhaust with too small wastegate. Your profile says 3" is that cat back or turbo back?

88BB8B · Jul 17, 2018

It is 3" turbo back. Should I replace the downpipe, or is there another way to fix it?

ThunderChild · Jul 17, 2018

Port the wastegate hole to a larger size to prevent boost creep and give the wastegate more control over exhaust flow.

pauleyman · Jul 17, 2018

On a t25 not sure I'd even be concerned. Is it causing you any issues?

88BB8B · Jul 17, 2018

Well I am concerned just because it will boost up to 20psi sometimes now, of course only briefly, but its stock fuel system, and 91 octane, so I assume it has to be kocking, or going dangerously lean at that boost level. Also, when I try to move the wastegate actuator by hand, I am unable, I'm thinking maybe its getting sticky, because it used to work just fine, only recently has it started doing this, so something like the 3" exhaust which was installed years ago would have shown a problem like this sooner, right?

ThunderChild · Jul 18, 2018

Do you mean when you have the wastegate actuator rod disconnected from the flapper arm, the flapper arm or the actuator rod doesn't move freely?

Inconsistent boost control would make me be tempted to look at the EBC parts, but if the wastegate is physically having issues, that's your problem.

88BB8B · Jul 18, 2018

When the actuator rod is connected to the flapper arm, the whole assembly won't budge at all. I didn't get around to disconnecting it to check which was sticky, if either. would it be okay to disconnect the EBC to see if the wastegate opens properly without it?

doubleclutch · Jul 18, 2018

The actuator arm is spring loaded and shouldn't be "moving freely". when connected. You can apply some pressure to it with a pump and see if it begins to open. You can also disconnect it from the flapper arm and make sure you flapper opens freely and completely.

I assume this has something to do with how your EBC is set. I use link for my boost control, but right around when the car can build full boost, I have to take out some duty cycle (boost essentially) to make sure i don't overshoot as boost is building.

All in all, at low rpms, 20 psi probably won't overwhelm your fuel system. TBH i am not sure the T25 can even flow enough air to max out the stock fuel set-up.

88BB8B · Jul 21, 2018

It wasn't boost creep, because the boost wouldn't increase as rpm did, and exhaust flow overwhelmed the waste gate port. Rather, it would spike when the throttle was pressed but it would hold at 15psi if I gradually built boost. It turns out it was the HKS boost controller, must've worn out or gotten clogged with something, I re-routed the hose driectly from the compressor housing to the waste gate actuator and it works perfectly now. I was surprised that it still makes 15-16psi when hooked directly to wastegate.

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Slight overboosting problem

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