Overboosting

[koston33]

Im running stage 2 + mscai. I've been spiking to 21-22 psi. Is there a reason why I'm hitting so high? What can I do with Tuner to lower my boost, so I don't spike as high?

 

[AutoEuphoria]

What mods do you have?

 

[koston33]

Mscai, cs tp, and cs dp

 

[koston33]

And mm and denzo spark plugs

 

[Sport6]

That means you are catless, and the Cobb tunes are meant to be used with catted downpipes. That is probably your number 1 problem.

 

[JOGADOGGZ]

These maps from Cobb are supposed to be followed exactly to specs based on there tuning. Dan from Cobb said you should follow there specs to get the peak levels of boost that they recommend. put your cat back on and you shouldn't overboost. if you continue to overboost you can run the risk of damaging your turbo/engine.

 

[koston33]

I'm asking how to Use atr to tune for a catless dp to stop over boosting

 

[AutoEuphoria]

I've asked the same question and haven't gotten a good response, other than adjusting the throttle - req load tables (press M for multiplier for cell, enter 0.95 to be 5% less in that cell) until it goes away. Not sure if there is a better way or other additional parameters that need to be changed as well.

 

[ballesteros_91]

im having the same damn problem

 

[koston33]

so autoeuphoria, did that see to work for you?

 

[AutoEuphoria]

I haven't received my link to download the ATR software yet. I sent the request in on Tuesday...resent it last night (in case I messed up the first time)...still no link. That is one of the things I am going to try, though

 

[MSMS3]

I'm asking how to Use atr to tune for a catless dp to stop over boosting

I have a catless exhaust (see sig). I do get spikes to 20-21 sometimes in very cold weather. But they are very quick and settle back down to 16 in my stock tune. In more typical weather, I spike to 18-19 and then quickly back down to 16.

When running catless, the real enemy is not the short momentary spikes when getting into boost, but rather a gradually increasing boost -- boost creep. Is your overboost short term boost spike or is it true overboost, which is also described as boost creep?

If you are getting boost creep where boost continues to climb and tries to hold above your target boost level, this is likely to be due to what a catless exhaust does to wastegate function - overwhelm it. In that scenario, the decreased backpressure (cats do provide a little backpressure), creates an increased flow rate that exceeds the bleed off abilities of the wastegate, even when it is wide open, and boost continues to build even after the ECU has told it to stop or hold at a predetermined level.

The only real cure for boost creep, if that is what you are getting is to modify the turbo itself by making the integrated wastegate port larger so that more exhaust can excape from the pathway of the turbine and out through the downpipe, or go to an external wastegate.

I think - repeat - think that you can tune somewhat for this with the AP, but don't know the details.

Temporary boost spike, quickly returning to your target boost is not typically going to be harmful to your engine. Boost creep up into your reported range is very definitely something to worry about.

I hope this is of some help. Maybe guys with catless systems and AP tuning can offer suggestions if you are getting true boost creep.

 

[Darth Vader]

I expect our mini-turbo will hit its surge line and lay down hard before it boost creeps to any meaningful degree. Spikes are pretty violent in cold weather and so is the smack off the boost cut when you bust 19.

 

[AutoEuphoria]

So far I've tried increasing the "Boost Dynamics" Correction Factor in the negative boost error region (where Actual > Desired), and lowering the boost comp A values in 3rd, 4th, and 5-6th by a factor of 0.95 in the RPM regions from 3k to 5500k. Seems like it might be making an effect, but it's not quite there yet. Last night it was creeping up past 21psi in third. Today it was creeping up past 19. It definitely needs some more work, but that does appear to have some effect.

Again, I'm new to it just like most people, so I'm just trying the logical steps and following the tuning guide. Take what I said with a large grain of salt, and try at your own risk.

EDIT: figured I should explain more. When I was testing last night in third I started at 2500RPM and logged the normal parameters, mainly AFR, knock retard, WGDC%, RPM, fuel pressure...I stopped my pull (in third) when I noticed my boost was getting too high. When I looked at the log it looked like the WGDC was still >0% when boost was going up past 19psi, so that's why I changed the boost dynamics curve and set the boost comp lower in those gears...basically, give it a lower boost in that gear in that RPM range and allow it to dump boost faster (if I am interpreting the guide right).

 

[COBB Tuning]

You need to discern between a boost spike, boost taper and boost creep. A spike in the tuning sense, is really a dramatic increase far beyond acceptable parameters. So, if you are hitting 2psi over your target here and there... I would not call that a "spike." Boost will always ramp up quickly on these small turbos so the "spikes" that most people refer to are not spikes at all, that is just the normal onset of boost with a smallish turbo on a relatively larger displacement engine.

This onset of boost WILL taper, the compressor and turbine are so small that they will not hold boost to redline. This is just the physics of these turbochargers.

Boost creep is where boost pressure rises at the top-end of the RPM band after the ECU has opened the wastegate. If boost continues to rise even though the wastegate is 100% open, then you have a mechanical issue where there is a high-pressure region around the wastegate that is not allowing exhaust gasses to bypass the turbine and instead, diverts exhaust gas back through the turbine causing an increase in boost pressure that cannot be "tuned out."

So we need to be careful when labeling these phenomena so that we can determine if there is an issue and what is going on exactly.

Travis
COBB Tuning

 

[matsuda]

How to test for boost creep:

Disconnect the wastegate solenoid valve (it takes 10 seconds).
If the boost rises above ~15.6 PSI at high loads...

 

[b00bs for n00bs]

You need to discern between a boost spike, boost taper and boost creep. A spike in the tuning sense, is really a dramatic increase far beyond acceptable parameters. So, if you are hitting 2psi over your target here and there... I would not call that a "spike." Boost will always ramp up quickly on these small turbos so the "spikes" that most people refer to are not spikes at all, that is just the normal onset of boost with a smallish turbo on a relatively larger displacement engine.

This onset of boost WILL taper, the compressor and turbine are so small that they will not hold boost to redline. This is just the physics of these turbochargers.

Boost creep is where boost pressure rises at the top-end of the RPM band after the ECU has opened the wastegate. If boost continues to rise even though the wastegate is 100% open, then you have a mechanical issue where there is a high-pressure region around the wastegate that is not allowing exhaust gasses to bypass the turbine and instead, diverts exhaust gas back through the turbine causing an increase in boost pressure that cannot be "tuned out."

So we need to be careful when labeling these phenomena so that we can determine if there is an issue and what is going on exactly.

Travis
COBB Tuning

what a good post.
spiking to 21-22 and tapering down to target is fine. have fun with atr, i never got into it when i had ap.

 

[MSMS3]

How to test for boost creep:

Disconnect the wastegate solenoid valve (it takes 10 seconds).
If the boost rises above ~15.6 PSI at high loads...

Matsuda, you have high cred in my book.

Question: is your your boost creep test parameter of stock 15.6 PSI still applicable for those of us running catless dp/rp, or should we expect to see the boost to rise and hold a bit higher, maybe two more pounds?

 

[coyfish]

Sometimes im getting boost creep on the stock tune. Usually its okay but sometimes when its cooler (at night) and im in 3-5th gear it will creep up to around 21-22. It happens basically a half a second before I shift around 5300 rpm. I usually shift at 5800. Its weird because it doesn't really "creep." It will all of a sudden jump from 17ish psi to 20-21 and I can feel the car pulling harder in that split second.

Most of the time its okay. This week has been pleasantly cooler ( i live in FL) and I ran a couple gears on my way home and experienced no issues. held at around 17.5 which was perfect.

You said this issue is mechanical and can't be tuned out which worried me. I have my ap sitting here uninstalled because im waiting on a downpipe to get custom tuned. Hopefully this issue isn't serious.

 

[JCurry]

port your wastegate...its how i got rid of all my boost creep problems on my 89 rx7....