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COBB Stumble kit


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Has anyone here used the COBB (or IAG or Radium etc) stumble kit on their LGT?  I've been told it's good, and told it's not necessary.  I'm looking for actual experience with them and did it actually work to fix the stumble like it supposedly does on 08-14 STis?

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I did the FPR swap from an STi and still have the stumble. I have tried everything under the sun and have never eliminated it. Something about the way the car detects knock at that RPM causes it to stumble. If you have an Accessport hooked up while going through that RPM range you'll see that thing light up at that RPM every time you go through it. 

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Hmmm... For $375 USD, I don't think I would buy the COBB kit... I ordered up an Sti FPR ($98 USD) and a couple of Turkeylord barbed tees. ($10 CAD each?).

Involves cutting and splicing fuel lines, which the kit does not.... But for ~$250 less? I think you should at least consider doing it yourself.

 

 

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32 minutes ago, Pleides said:

I did the FPR swap from an STi and still have the stumble. I have tried everything under the sun and have never eliminated it. Something about the way the car detects knock at that RPM causes it to stumble. If you have an Accessport hooked up while going through that RPM range you'll see that thing light up at that RPM every time you go through it. 

I've had the stumble for a while, and while getting it tuned recently for TBE, my tuner definitely noticed it.  He said it seems to be when switching from closed to open loop in the fpr.  He mentioned the stumble kit has worked on STis he has tuned and since we are the same setup he figured it would be worth a shot.

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22 minutes ago, GearJamr said:

I've had the stumble for a while, and while getting it tuned recently for TBE, my tuner definitely noticed it.  He said it seems to be when switching from closed to open loop in the fpr.  He mentioned the stumble kit has worked on STis he has tuned and since we are the same setup he figured it would be worth a shot.

My car has been tuned several times with the FPR and it has never gone away. Mostly comes up after a few miles of driving after a tune.

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I have the iridium STI FPR kit, Iridium Full fuel system, Rails and lines. I am also pro-tuned. I do not have a stumble that I notice. I also have the IR gauge. I will getting a revision next month and will check on this for you all and let you know.

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1 hour ago, GearJamr said:

... He said it seems to be when switching from closed to open loop in the fpr...

Our cars have a variable speed fuel pump controlled by the Fuel Pump Driver Module (22648AA081), I think the fuel pump voltage is varied based on a output from the ECU. Maybe there is a issue with the pump volume/pressure in the transition between open and closed loop fueling? Anybody ever monitored fuel pressure through this issue? I wonder if watching the fuel pump voltage would tell us anything?

I know that my car (OTS stage II Cobb tune) struggles with the open/closed loop transition to boost at times, it would nice to have a solution.

 

Gary

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2 minutes ago, All_talk said:

Our cars have a variable speed fuel pump controlled by the Fuel Pump Driver Module (22648AA081), I think the fuel pump voltage is varied based on a output from the ECU. Maybe there is a issue with the pump volume/pressure in the transition between open and closed loop fueling? Anybody ever monitored fuel pressure through this issue? I wonder if watching the fuel pump voltage would tell us anything?

I know that my car (OTS stage II Cobb tune) struggles with the open/closed loop transition to boost at times, it would nice to have a solution.

 

Gary

I do remember some one in the past talking about the fuel pump and that fixed their issue. I have a big pump and i have no problems. I did mention this when they built the car.

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I did some reading on outback site I believe, maybe nasioc.  It was an older post but they were saying a catless up-pipe resolved a lot of the stumbling issues.  I'll be having that done in a couple weeks, so I might just wait and see.

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3 hours ago, Pleides said:

I did the FPR swap from an STi and still have the stumble. I have tried everything under the sun and have never eliminated it. Something about the way the car detects knock at that RPM causes it to stumble. If you have an Accessport hooked up while going through that RPM range you'll see that thing light up at that RPM every time you go through it. 

Well that’s not inspiring. I’ve owned and driven several ej257 that didn’t have as much as a stumble. Is the issue in the airflow then?

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3 hours ago, All_talk said:

Our cars have a variable speed fuel pump controlled by the Fuel Pump Driver Module (22648AA081), I think the fuel pump voltage is varied based on a output from the ECU. Maybe there is a issue with the pump volume/pressure in the transition between open and closed loop fueling? Anybody ever monitored fuel pressure through this issue? I wonder if watching the fuel pump voltage would tell us anything?

I know that my car (OTS stage II Cobb tune) struggles with the open/closed loop transition to boost at times, it would nice to have a solution.

 

Gary

There was a whole thread about how the oscillation was recorded at Cobb Surgeline years ago and that the solution for many was to install a certain vacuum line T to move the source for vacuum around. I can't seem to find it, but I swear the person that made the custom vacuum T was named Turkey something or other.

 

2 hours ago, blackobxt said:

Well that’s not inspiring. I’ve owned and driven several ej257 that didn’t have as much as a stumble. Is the issue in the airflow then?

It's an issue with fuel pressure. The ECU on our cars has a damn hard time figuring out how much to give at that RPM range and seems to cause the engine to knock, so the ECU can never figure out whether to advance or retard timing in this RPM range and dilution of the AFR doesn't always work due to whatever fuel pressure issue occurs. This is all I can remember off the top of my head. There was a whole thread dedicated to the stumble at the low 2K RPM range that many people struggled to solve. I have personally spent thousands of dollars and many of my own hours working on the car to try to fix the stumble. It has never gone away. It actually got substantially worse when I installed ID1050X. After tuning, the car has never driven smoothly.

I think the real answer to all this is to leave the car stock and then install the FPR and the vacuum T mod. But I have both those things and a few other mods to accompany my VF52 and I've just had to learn to live with it.

Edited by Pleides
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3 hours ago, Pleides said:

There was a whole thread about how the oscillation was recorded at Cobb Surgeline years ago and that the solution for many was to install a certain vacuum line T to move the source for vacuum around. I can't seem to find it, but I swear the person that made the custom vacuum T was named Turkey something or other.

 

It's an issue with fuel pressure. The ECU on our cars has a damn hard time figuring out how much to give at that RPM range and seems to cause the engine to knock, so the ECU can never figure out whether to advance or retard timing in this RPM range and dilution of the AFR doesn't always work due to whatever fuel pressure issue occurs. This is all I can remember off the top of my head. There was a whole thread dedicated to the stumble at the low 2K RPM range that many people struggled to solve. I have personally spent thousands of dollars and many of my own hours working on the car to try to fix the stumble. It has never gone away. It actually got substantially worse when I installed ID1050X. After tuning, the car has never driven smoothly.

I think the real answer to all this is to leave the car stock and then install the FPR and the vacuum T mod. But I have both those things and a few other mods to accompany my VF52 and I've just had to learn to live with it.

Out of curiosity, have you monitored fuel pressure on an analogue gauge? In theory it should be a simple problem to solve. My car is for the most part stock and I’ve felt it every step of the way. From stock tune to my full tune it’s been there. However our previous outback that was “built” and had an adjustable fpr and a walbro 255 had no stumble at all

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1 hour ago, blackobxt said:

Out of curiosity, have you monitored fuel pressure on an analogue gauge? In theory it should be a simple problem to solve. My car is for the most part stock and I’ve felt it every step of the way. From stock tune to my full tune it’s been there. However our previous outback that was “built” and had an adjustable fpr and a walbro 255 had no stumble at all

I have not. If there isn't software built-in to monitor fuel pressure then my car hasn't.

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In the link above, On Aug 3rd 2022 I posted a link. Reset the ECU after you install the T and plug the port on #4 intake runner. 

first photo is my 2009. I'll try and edit in photo of my 2005 set up

 

DSCN7341.JPG

DSCN9873.JPG

DSCN9875.JPG

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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20 minutes ago, Max Capacity said:

In the link above, On Aug 3rd 2022 I posted a link. Reset the ECU have you install the T and plug the port on #4 intake runner.

 

DSCN7341.JPG

I’m currently in this configuration and no big changes to the stumble. 

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Sorry to hear it didn't work for you. Both my cars have this MOD.

 

I also fixed the typo in my thread, after reading your quote. Gee, this old age stuff is tough. 

  • Like 1

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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6 hours ago, Max Capacity said:

In the link above, On Aug 3rd 2022 I posted a link. Reset the ECU after you install the T and plug the port on #4 intake runner.

 

DSCN7341.JPG

My point of this thread was to see if anyone had used the stumble kit from COBB (or others).  Not to rehash what is in the stumble thread.  :)

However, I appreciate the discussion.  Max Capacity's solution seems the simplest and least likely to mess something up.

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I'll say, the wagon responded better than the Spec B did to the T fitting. In the Spec, on the up hill grade about a 1/2 mile from the house, when the engine is cold, I can feel a very mild stumble. But I know what I'm looking for. That cold hill climb is the only place I feel the very slight stumble in the Spec B. The passenger in the car doesn't feel anything.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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If fuel pressure is the issue I wonder if you could bypass the FPCM and run the pump a 100% just to see if it solves the problem?

Do Cobb or open source tunes have access to the ECUs output to the FPCM?

Looking at the wiring diagram (included) it looks like there are two wires from the ECU to the FPCM, one or both of them must control the pump voltage (PWM). At the least we should be able to monitor the signal during the stumble and see if something correlates.

FPCM.pdf

Edited by All_talk
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I know I have talked with my Tuner about it. I do believe he made some adjustments for the stumble. tuningalliance@gmail.com  He's still doing Tunes while raising his family and working, but has more knowledge about Tuning these cars than most. He has a Forum in the Vendor forum. 

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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  • 3 weeks later...
On 8/11/2022 at 9:06 AM, Max Capacity said:

In the link above, On Aug 3rd 2022 I posted a link. Reset the ECU after you install the T and plug the port on #4 intake runner.

 

DSCN7341.JPG

Okay, so this picture shows something different from the thread covertrussian made about the install here: 

In his thread the T connector is installed in the line off the BOV, but the other routes directly to the FPR.  In your picture the other hose runs off under the intake and I don't recall seeing that hose in my 05 wagon.  Would it really matter which way it's done?

 

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