06 STI VACUUM Hesitation

[P3Auto]

Intermittent leaks will not show up always, especially if they may only happen during open loop fueling. Remember leaking BPV or failing BPV is already metered air getting recirculated.

Based on what I see here so far and the little I know about this car it seems the BPV is a possible issue. As I have mentioned I have personally had cars in the shop that would surge, shudder, and or hesitate when the BPV was doing something strange. If you look at whats going on during part throttle boosting its quite a balancing act. Intake turbulence from recirculating air can cause all sorts of fun things to happen.

I'm not ruling out other possible issues, heck it could even be a damage turbine wheel. Who knows its hard to play doctor when your thousands of miles away...lol

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[Daluv]

Hesitation alway occurs:

- in Close Loop
- light load 0.3-0.4
- Vacuum around -10 PSI
- 2000-3200 RPM

Once I go in Open loop, the car accelerate fine.

Mart

Originally Posted by P3Auto

Intermittent leaks will not show up always, especially if they may only happen during open loop fueling.

Based on what I see here so far and the little I know about this car it seems the BPV is a possible issue. As I have mentioned I have personally had cars in the shop that would surge, shudder, and or hesitate when the BPV was doing something strange. If you look at whats going on during part throttle boosting its quite a balancing act.

I'm not ruling out other possible issues, heck it could even be a damage turbine wheel. Who knows its hard to play doctor when your thousands of miles away...lol

[P3Auto]

Alright. Cap the recirc line from the BPV to the intake and cap the BPV. Lets rule this thing out. This test would take a few mins to do if you can find a cap for the end of the hose. While you have the hose off and the car running put you hand over the open end of the BPV and see if you feel any air being moved. At idle the valve should be shut.

Once you have the line capped off go drive around. Avoid excessive boost just try the areas you have the problems in.

If the problems still exist I would visit the MAF. Swap with a known good one. Sometimes depending on the intake configuration you can get turbulence around the MAF sensor, swirling air , etc. This is why some people have had to put in air straighteners, screens before the sensor and other methods. I realize you have logged this and see nothing but you also have to remember that at low loads like this the computer will respond and could make decisions much faster then you can log it.

One last thing...You can go into open loop at low loads as well depending on variables in the tune. Don't always assume your on closed loop especially if you zeroed the OL/CL delay tables.

[Daluv]

I will try the BPV trick.

I have swap with a working MAF, same problem.
I have run without a MAF, same problem.
I have run without a front 02, same problem.
I have run without the rear 02, same problem

I have developped a tool of my own monitoring important parameters and displaying it real-time talking SSM. That's how I know that:

hesitation alway occurs:

- in Close Loop
- light load 0.3-0.4
- Vacuum around -10 PSI
- 2000-3200 RPM

thanx you for your input.

Mart

Originally Posted by P3Auto

Alright. Cap the recirc line from the BPV to the intake and cap the BPV. Lets rule this thing out. This test would take a few mins to do if you can find a cap for the end of the hose. While you have the hose off and the car running put you hand over the open end of the BPV and see if you feel any air being moved. At idle the valve should be shut.

Once you have the line capped off go drive around. Avoid excessive boost just try the areas you have the problems in.

If the problems still exist I would visit the MAF. Swap with a known good one. Sometimes depending on the intake configuration you can get turbulence around the MAF sensor, swirling air , etc. This is why some people have had to put in air straighteners, screens before the sensor and other methods. I realize you have logged this and see nothing but you also have to remember that at low loads like this the computer will respond and could make decisions much faster then you can log it.

One last thing...You can go into open loop at low loads as well depending on variables in the tune. Don't always assume your on closed loop especially if you zeroed the OL/CL delay tables.

[P3Auto]

Well it sounds like you have covered a lot of the bases then. If your able to log quickly I find in hard to believe you don't see something standing out while this is happening.

Did you try roughness monitoring on each cyl? Look for one that stands out and check plug, coil, and injector.

If you can isolate a cyl then you just move the coil pack to a difference cyl and see if the roughness moves, then do the same with the injector as well. This method would help identify a leaking injector or bad coil back or even a plug.

[Daluv]

I cannot log faster than romraider ( 4800bauds limit) with my tool. My next project is to overwrite the baud rate in the ecu to help resolution. I got an ecu on my bench and I am only missing some times at this point. It has been done by Freon a little while ago.

I did log Roughness on each cylinder while hesitation and I had no hit at all.

Mart

Originally Posted by P3Auto

Well it sounds like you have covered a lot of the bases then. If your able to log quickly I find in hard to believe you don't see something standing out while this is happening.

Did you try roughness monitoring on each cyl? Look for one that stands out and check plug, coil, and injector.

If you can isolate a cyl then you just move the coil pack to a difference cyl and see if the roughness moves, then do the same with the injector as well. This method would help identify a leaking injector or bad coil back or even a plug.

[NSFW]

Originally Posted by P3Auto

Swap your BPV with someone and see what happens. Part throttle can cause the valve to open and close or even cycle strangly. This in turn plays havoc on the ECU. I have run into this problem (exactly as described) with badly adjusted blow off valves and by pass valves..

Stop messing with the tune. If it does it stock then you have a mechanical (physical) problem. Although you may find some magical way to tune it out nothing you have added should make this a problem.

I don't see how BPV recirculation would affect fueling. Yes the air is metered, but it's only being recirculated right back into the metered stream. The amount of air going into the engine is still going to be equal to the amount of air that's going past the MAF sensor. And keep in mind that under the conditions where this happens, there's little or no pressure differential across the BPV's flow path. So even if it does open, little or no air is going to move.

This hesitation is a fairly common problem with stock Subarus. There are a bunch of threads about it on LegacyGT.com, those cars seem to be particularly prone to it. It doesn't happen to everyone, only a minority, but it happens often enough to stock cars that I don't think it makes sense to assume that the problem is or isn't mechanical in nature. I suspect that there is a mechanical aspect to it, just because hardware varies more than software... but not by much.

Some people have claimed that the problem went away with a tune. However people have also reported that the problem came back after a while, which leads me to think that it just doesn't happen consistently enough for anyone to really know what's up.

It's common enough that whoever gets to the bottom of this will gain instant fame.
Almost makes me wish my car had this problem, just so I could really get to work on it.

[Daluv]

I can try whatever you want

Originally Posted by NSFW

It's common enough that whoever gets to the bottom of this will gain instant fame.
Almost makes me wish my car had this problem, just so I could really get to work on it.

[Daluv]

I was about to pull the trigger on a Forge BPV but now I am confused

[Phatron]

Originally Posted by NSFW

It's common enough that whoever gets to the bottom of this will gain instant fame.
Almost makes me wish my car had this problem, just so I could really get to work on it.

I thought the MRP based fuel trim tables was curing it for most people?

Get the MRP log done again Martin.....

[Daluv]

it is actually zero'd out. So yes, maybe I should try it now since LearningView data is stable ( within +/- 2% ) since a little while...

Originally Posted by Phatron

I thought the MRP based fuel trim tables was curing it for most people?

Get the MRP log done again Martin.....

[Daluv]

A quick google search for "BPV Hesitation" gives several people claiming that putting a FORGE BPV cures their hesitation problems.... now is it true...

Mart

Originally Posted by NSFW

I don't see how BPV recirculation would affect fueling. Yes the air is metered, but it's only being recirculated right back into the metered stream. The amount of air going into the engine is still going to be equal to the amount of air that's going past the MAF sensor. And keep in mind that under the conditions where this happens, there's little or no pressure differential across the BPV's flow path. So even if it does open, little or no air is going to move.

This hesitation is a fairly common problem with stock Subarus. There are a bunch of threads about it on LegacyGT.com, those cars seem to be particularly prone to it. It doesn't happen to everyone, only a minority, but it happens often enough to stock cars that I don't think it makes sense to assume that the problem is or isn't mechanical in nature. I suspect that there is a mechanical aspect to it, just because hardware varies more than software... but not by much.

Some people have claimed that the problem went away with a tune. However people have also reported that the problem came back after a while, which leads me to think that it just doesn't happen consistently enough for anyone to really know what's up.

It's common enough that whoever gets to the bottom of this will gain instant fame.
Almost makes me wish my car had this problem, just so I could really get to work on it.

[P3Auto]

Originally Posted by Daluv

A quick google search for "BPV Hesitation" gives several people claiming that putting a FORGE BPV cures their hesitation problems.... now is it true...

Mart

I really have seen and fixed personally in my shop the BPV causing the exact issues as I mentioned before. Its very common with after market mis adjusted valves.

I have tuned and worked on dozens of Subarus and have never run into this issue with a stock setup unless the stock valve was faulty or modified..Crushed BPVs do this as well.

I notice your using learning view to determine fueling trims, keep in mind this is only an averaged snap shot. The short term trims are still applied on top fairly quickly but not enough to effect the long term averaged trims.

Not sure if you have tried a log of just MAF volts but you may want to look for flat spots or signs of turbulence as I mentioned can also cause this. A swap with a stock air box may be worth the effort if you have not tried that yet.

I think your problem will end up being a simple fix once you find it.

[Daluv]

I have logged MAF voltage and everything was fine. I swapped with another MAF with no changes at all.

I do run a stock airbox with a Perrin foam filter now (had a k&N before)

the FORGE BPV... uhm...

Mart

Originally Posted by P3Auto

Not sure if you have tried a log of just MAF volts but you may want to look for flat spots or signs of turbulence as I mentioned can also cause this. A swap with a stock air box may be worth the effort if you have not tried that yet.

I think your problem will end up being a simple fix once you find it.

[P3Auto]

Before I spent the cash on a forge bpv I would buy a used STI valve from the forums. I have seen them for $25. Good luck and keep us updated.

[Daluv]

yeah but I dont want to get a faulty used one...

Originally Posted by P3Auto

Before I spent the cash on a forge bpv I would buy a used STI valve from the forums. I have seen them for $25. Good luck and keep us updated.

[Daluv]

that is right. Learningview is just another way to confirm that I have no leaks (unmetered air). I do notice a jump in the AF Correction when the hesitation usually occurs. Also, when I left the gas off and go back... I can clearly see that with my SSM monitor tool live.

Mart

Originally Posted by P3Auto

I notice your using learning view to determine fueling trims, keep in mind this is only an averaged snap shot. The short term trims are still applied on top fairly quickly but not enough to effect the long term averaged trims.

[P3Auto]

It would be rare unless it was modified. Most people pull them off working fine to replace them with after market ones.

One more thought, If you can get a wideband gauge (borrowed or bought) it would be interesting to see the fuel reading during the hesitation if you can keep it going for a long enough to read.

[P3Auto]

Which way does the correction go when you get the hesitation. negative or positive and how much. If you still in closed loop you can log the #1 O2 sensor and that will show a very accurate fuel reading. I find these cars are slightly delayed with the short term trims and they can trim after the event which then leads to a new event if the trim is nasty enough.

Originally Posted by Daluv

that is right. Learningview is just another way to confirm that I have no leaks (unmetered air). I do notice a jump in the AF Correction when the hesitation usually occurs. Also, when I left the gas off and go back... I can clearly see that with my SSM monitor tool live.

Mart

[Daluv]

I do have an LC-1.

Originally Posted by P3Auto

It would be rare unless it was modified. Most people pull them off working fine to replace them with after market ones.

One more thought, If you can get a wideband gauge (borrowed or bought) it would be interesting to see the fuel reading during the hesitation if you can keep it going for a long enough to read.

[Daluv]

From what I recall, it is positive.

Originally Posted by P3Auto

Which way does the correction go when you get the hesitation. negative or positive and how much. If you still in closed loop you can log the #1 O2 sensor and that will show a very accurate fuel reading. I find these cars are slightly delayed with the short term trims and they can trim after the event which then leads to a new event if the trim is nasty enough.

[Phatron]

Mart, are you sure you're in closed loop? Your time delays are 0, so any pedal % should throw you into OL immediately.

Can you do a hesitation log and log the CL/OL parameter and all the fueling parameters.

[Daluv]

From my live experience using my SSM tool (even with time delay to 0), you can stay in Close loop with light pedal input. There is more than that in the algorithm to makeit switch I believe.

Originally Posted by Phatron

Mart, are you sure you're in closed loop? Your time delays are 0, so any pedal % should throw you into OL immediately.

[Daluv]

yes, I will do.

Originally Posted by Phatron

Can you do a hesitation log and log the CL/OL parameter and all the fueling parameters.

[Phatron]

from my experience...even within the last couple weeks logging my neighbors 06 sti....you pretty much have to be at a constant throttle input....or coming down from say12% to 10% to be in CL.....if the throttle % is increasing it should kick you into OL pretty fast.

His car was going ol cl ol cl ol cl ol cl ol cl every second or two.....so if you're just glancing over at your ssm monitor you wouldnt really notice that