Over boosting Issues

[Bang876]

So I have notice that on the 08+ STi tend to have over boost issues. I wanted to get some input and opinion from others who may have experience this issue and how did you fix it.

Mod List:

Cobb Intake w/ Airbox
Cobb Boost Solenoid
FIC 1100 cc injectors
Turbo XS Turboback Catless
Walbro 460lph fuel pump
Stock BOV

Alright the problem started to occur shortly after my tuner raised the boost level up to 21psi. The car ran fairly smooth when I was running the COBB Stage 2 map but once we got the boost up, the car had over boosted more often. Not to say that is occurs every time I drive but it occurs enough for me to notice. Like if am in 4 or 5 gear at low rpm and give it gas the car stutters and check engine light pops on and sure enough its always the over boost cell code. I also occurs even at lower gear when when I go WOT. I know having a catless TBE has an effect but I was wondering would possible changing the BOV to a 50/50 help or would I have to take the expensive route and go EWG. I don't plan on going any more power wise and just want this boost issue resolve. Let me rephrase that its not really a bad issue but I want to try to minimize any problem that could cause my car to knock.

 

[Boogieman98]

I have a 13 STi and I went with a EWG setup to fix it. You could port out the IWG on the stock turbo and that should fix it from what I have heard

 

[Alin]

Im certain our wise men will chine in sooner or later. It wouldnt be from the stock bpv as that holds up pretty well for what it is. Your catless has a role in this but it also depends on the tune of the car. Lets get some input!
[MENTION=1507]Spamby[/MENTION] [MENTION=652]Grinder34[/MENTION] [MENTION=662]Batmobile_Engage[/MENTION] [MENTION=1]IGOTASTi.COM[/MENTION] [MENTION=9]HolyCrapItsFast[/MENTION] [MENTION=3516]zax[/MENTION] [MENTION=1345]fuji_production[/MENTION]s [MENTION=3416]WRB_STi[/MENTION] [MENTION=1069]35r[/MENTION]

 

[Batmobile_Engage]

I would say this issue is a combination of things, but still could be managed in the tune. George would know better than I. Have you considered a manual boost controller?

 

[Spamby]

I've only had slight overboost like 1 or two psi and only during really cold weather and giving a high gear romp. Very rare occasion. At least perceived with my boost gauge which in all honesty may be off a bit. I'm on a catless setup and I just don't have these issues. Weird?
I'd see if your tuner could help alleviate this.
If it can't be resolved, I'd try porting the wastegate.

 

[Alin]

Also be a little more specific. If your target is 21 psi, how much are you overboosting to?

 

[Boogieman98]

Has this happened when it is warm outside? Mine would only over lost when it was below 60 degrees.

 

[Grinder34]

Like if am in 4 or 5 gear at low rpm and give it gas the car stutters and check engine light pops on

4th gear is fine, but really avoid giving the car gas at low RPMs in 5th and 6th. From everything I've read, its bad for the engine. Let me see if i can dig up the technical discussion on it.

Oh, it was in this thread, which may be of interest to you anyways:

http://igotasti.com/vBforum/showthread.php?6938-Potential-Causes-of-Overboosting

Quote of interest (end of pg 3):

The reason why overboosting in the longer gears is so likely to happen is because as your pushing the gas pedal to the floor your telling the ecu hurry up and accelerate and since it cant do that because you are in a longer gear the TD is trying to adjust accordingly to compensate for the longer gear acceleration which isnt what it is designed to do in the first place and that is where you get your overboost. You can combat this action by lowering the duty cycles but now you are moving into the territory of underboosting and losing responsiveness. Its hard to explain and i know im not very technical but i tried my best...

 

[Alin]

4th gear is fine, but really avoid giving the car gas at low RPMs in 5th and 6th. From everything I've read, its bad for the engine. Let me see if i can dig up the technical discussion on it.

Oh, it was in this thread, which may be of interest to you anyways:

http://igotasti.com/vBforum/showthread.php?6938-Potential-Causes-of-Overboosting

Quote of interest (end of pg 3):

High gear + High Load + low air temps = high boost.

The air is very dense compared to when it was originally tune, would be my guess. If you are tuned to maintain a waste gate duty of say 75% during WOT, the turbo will spin at a certian speed and it won't change much from that during the year. As the air becomes dense your turbo will output more air while miantaining the same speed, hence the increase in boost. Now add on top of that 5th gear high load. Now the ECU and turbo are striving to increase even more boost to keep up with the demand in load. You can easily run into an over boost situation under these conditions with out the proper compensation. There are compensations available for AIT in the GD and both AIT and Gear in the GR.

For tuners that don't really know how to use the factory boost control they accept that there will be changes in boost during the year and that the "Target" is just a guide line and not written in stone. They usually tune below target in the summer month to maintain a best range through out the year or tune to target or slightly higher during winter months. During spring and fall are the beat times to tune to target because you will swing marginally from +/- target during the year versus having it tuned in the summer to target and risk swinging to far above target in the winter. The other solution is to have a tune for summer tuned to target and one for winter tuned to target.

Since your issue is largely due to load related demand your situation is dificult to compensate for because the tables for per gear requested torque are not present in your year.

:tup:

Only reason you would be in 5th gear at WOT is because you're going at least 100 MPH.

 

[fuji_production]

downshift men!!!

 

[Alin]

downshift men!!!

In all seriousness, you must be at a higher RPM before inducing WOT!

 

[Batmobile_Engage]

:tup:

Only reason you would be in 5th gear at WOT is because you're going at least 100 MPH.

I still overboost in 5th at over 100mph, but it's built into my tune.

 

[Alin]

I still overboost in 5th at over 100mph, but it's built into my tune.

That's odd. 4th ends at 90/100 and in 5th gear, you should be right around 4.5-5k RPM at that speed if I'm not mistaken.

How much over target boost do you go to?

 

[Batmobile_Engage]

About 2 psi over target.
19psi 1st-4th gear, 21psi in 5th and 6th. Once I get up around 6k, it starts to settle back under 20.

 

[Alin]

About 2 psi over target.
19psi 1st-4th gear, 21psi in 5th and 6th. Once I get up around 6k, it starts to settle back under 20.

Is 2 psi over on your current set up anything to be concerned about?

 

[Batmobile_Engage]

If my tuner didn't factor it in, it'd be a problem. It probably helps that my methanol system is spraying full blast at that point as well.

 

[Bang876]

Cool thanks for then input and help everyone.

 

[HolyCrapItsFast]

Is 2 psi over on your current set up anything to be concerned about?

As long as timing and fuel are OK I would say extra boost = bonus :tup:

 

[Alin]

As long as timing and fuel are OK I would say extra boost = bonus :tup:

[MENTION=662]Batmobile_Engage[/MENTION]

Did you notice anything out of the ordinary during that extra 2 psi pull? (Did you log it at least?)

 

[Batmobile_Engage]

No, nothing weird. I need to send my AP back to Cobb for repair/replacement. When its back, I can probably log.