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Old 08-16-2011, 10:05 PM   #1
RoninSTI
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Default Fixing the GR 2400-3000rpm stumble with Accessport

DISCLAIMER: This is not a "how-to", this is documentation on how I used information on the interwebs to solve the 2400-3000 rpm low load acceleration stumble on my 2011 STI. YOU are responsible for any changes you make to your maps.

The issue:
The GR stumble is an issue that is not detrimental to the car, just annoying to deal with. It happened to me just about everyday when driving normally. Under light load, partial throttle (at about 2800 rpm) the car would hiccup or stumble for a moment. After doing tons of searches on here, IWSTI and Rom raider, I took existing information and eliminated the stumble on my car. The result is beautifully smooth, low rpm, partial throttle acceleration.

Reference material:

I read, and re-read every post in the following threads...

http://www.iwsti.com/forums/ecu-tuni...-using-ap.html
http://www.romraider.com/forum/viewt...ff6e4726adba13

Tools Required:
1) The spreadsheet located here
http://www.romraider.com/forum/viewt...hp?f=32&t=5483

2)Cobb Accessport
3)Windows Based Excel (I used Excel 2007 on a virtualized version of windows XP on a mac)
4)Basic excel data manipulation abilities
5)Accesstuner Race (free download from cobb's website)
6)Ability to Datalog using Accessport

The Datalog:

I logged the following parameters:
A/F Correction 1
A/F Learning 1
A/F Sens 1 Ratio
Boost
MAF Voltage
RPM
Throttle Position

Also the "live" parameter I made note of while logging was the barometric pressure. I need that number for the spreadsheet. I logged for at least an hour or so of highway driving. I went through most of the rpm range from 2000-4000 in 4th, 5th, and 6th. I dwelled for a while at each rpm for each gear. I spent a couple minutes around 55mph, 60mph and so on. I needed enough data points for the spreadsheet to get enough of a sample to size to make the averages.

Data Manipulation:

1) Once I had my log, I renamed the headers of each column to EXACTLY the same as the spreadsheet. I saved in csv format.
2) I opened the romraider spreadsheet, made sure I enabled macros, and clicked "clear and get data". I located my modified header csv file. I entered the barometric pressure into the box. (for me 14.5 psi).

This is where it gets a bit complicated, but once I was in the files it made sense...

3) I opened my Stage 1 OTS map from cobb (Stage 1 93 octane boost select). I opened the sensor calibration folder and opened the table labeled "load compensation (cruise)"
4) I copied the first row (the headers) and copied into a blank spreadsheet. I then made the following conversion to each number. Note the header title is a pressure in BAR. I called the header number X. The barometric pressure I logged was Y. The conversion is: (X*Y)-Y. The conversion makes a new row of headers. I copied that row as new headers into the tab labeled "ROM". The ROM tab is just used for the pivot table. Now the pivot table that the spread sheet generates matches the numbers in my cobb table.
5) I went back to the input tab and clicked filter. After the calculation was complete, the pivot table generated is on the EL comp tab. Its the top table labeled average correction.
6) notice the pivot table is full of bold, grey and empty cells. The empty cells had no data, the gray cells didn't have enough samples for an average, and the bold cells are valid data. I didn't worry that not all the cells had data, most did, I think it might be next to impossible to get data for EVERY cell.
7) I copied the entire load comp cruise table into a new spreadsheet, rpm titles and headers included.
8)Next to it on the same spreadsheet, I copied the pivot table, I made sure to line up the pivot table on the appropriate rpm row. The pivot table doesn't have data for every corresponding cell on the cobb table. It's only concerned with a certain portion of the table. So I made the pivot table equal in rows and columns as the cobb map, i simply made every empty cell 0, and every cell with a gray number 0.
9)So now i had two tables, with the same headers and row labels, the exact same size, side by side. One table is the table from the cobb map, one table is the pivot table with a bunch of zeros added to make it the same size as the cobb table.
10) I made a third table under the cobb table, same headers and rpm labels. I made the first cell equal to the value of the first cell on the cobb table PLUS the value of the first cell from the pivot table. I then dragged the formula across the row, then down the columns. (please reference excel for dummies lol).
11) I copied the new table into access tuner race (values only).
12) I Repeated the process for the accel table. (get the new headers, do the conversion, paste new values into ROM table, filter data, get new pivot table, add pivot table to existing map, paste new map into access tuner).
13) I saved the map with a new name
14) I flashed the new map, went for a cruise and voila! NO STUMBLE.

I think this may be an iterative process, I may perform all these steps again to see if anything changes, or just datalog again and look at the graphs in the spreadsheet to ensure there are no outliers anymore.

Hopefully this documentation will help others diagnose and fix the same issue on their car. FYI, this was the first time I changed any of the tables in access tuner and it couldn't have been easier.

I'm still re-reading the reference material to determine exactly why this eliminates the stumble.

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Old 08-18-2011, 08:07 AM   #2
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nice, i wonder if this will work for the older sti and fxt
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Old 08-18-2011, 10:58 AM   #3
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very nice write up.

i also have that issue on my 2011 sti. i will try it someday.
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Old 08-18-2011, 06:51 PM   #4
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i have this problem also on my 04xt. im going to the tuner in 2 weeks to get a brush up tune. ill see if i can get him to read this thread because its over my head. is there something easy i can tell him to check like cliffnotes to what you posted above in case we dont get a chance to read the above?
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Old 08-19-2011, 07:13 AM   #5
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^^^ these are the cliffnotes.....if you what the whole story read the 16 pages of posts on the romraider link he provided above
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Old 08-19-2011, 09:42 AM   #6
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Quote:
Originally Posted by eduSti View Post
^^^ these are the cliffnotes.....if you what the whole story read the 16 pages of posts on the romraider link he provided above
Haha exactly, this is a very brief overview of the steps I took to correct the issue. The 16 pages over at rom raider and the 4 or 5 pages on the spreadsheet link are really worth the read if you're going to attempt this.

I'm still re-reading the threads to fully understand the issue and the fix, even though my is car running great.
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Old 08-19-2011, 05:33 PM   #7
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sorry, i dont know squat about tuning. i was just trying to make it easy for my tuner to try it. ill mention it to him. it seems more people are coming out with the same hesitation problems here lately
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Old 08-20-2011, 09:47 AM   #8
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Quote:
Originally Posted by spec_bg View Post
sorry, i dont know squat about tuning. i was just trying to make it easy for my tuner to try it. ill mention it to him. it seems more people are coming out with the same hesitation problems here lately
No worries. Ask your tuner if he's familiar with using the load compensation tables to fix the stumble. If he's not, refer him to the rom raider thread. A competent tuner should be able to understand what's being discussed in there no problem. I am not a tuner by any stretch of the imagination, but I was able to piece together what was going on.

Hope this helps.

Also start doing your logs now before you go to get tuned. You need at least an hours worth of data. Better safe than sorry to have the logs for your tuner and not need them.

Last edited by RoninSTI; 08-20-2011 at 09:49 AM. Reason: Add info
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Old 02-04-2012, 04:54 PM   #9
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For the FXT, it is unlikely that this will fix the problem of hesitation, this problem is only evident in 08+WRX's and STI's. It is much worse with the STI's. With The WRX you just get wide fuel trims but very little hesitation. For the most part the WRX hesitations were fixed by the per injector pulsewidth compensation tables from the factory.
You can also use this spreadsheet to change the per injector pulsewidth compensation tables as well.

For the earlier cars without this issue. You can use this technique to create a more stable maf scale and minimize and stabilize AF Learning.

I wish we could truly find the cause of this. We only have a few band-aid fixes, by forcing the car to add fuel when it shouldn't need to. When you upgrade injectors on STI's this gets out of hand. I have tuned cars with fuel rails and aftermarket fpr's, Changed the Fuel Pump Duties. Altered the dual AVCS tables in every direction. The problem always persists.
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Old 12-28-2012, 11:37 AM   #10
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The problem is a standing wave in the fuel line. You can make it totally go away by removing the 8" piece of fuel line running from the damper to the hard line on the manifold and replacing it with a ~3' section of fuel line. Zero the load compensation tables and it is totally gone.

Thread here starting at post #13:
http://www.iwsti.com/forums/2-5-lite...lean-spot.html
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Old 12-28-2012, 03:00 PM   #11
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Quote:
Originally Posted by tshrey View Post
The problem is a standing wave in the fuel line. You can make it totally go away by removing the 8" piece of fuel line running from the damper to the hard line on the manifold and replacing it with a ~3' section of fuel line. Zero the load compensation tables and it is totally gone.

Thread here starting at post #13:
http://www.iwsti.com/forums/2-5-lite...lean-spot.html
I have found this to be the very best fix to date as well. Works perfect on stock injectors and aftermarket as well.
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Old 12-28-2012, 03:42 PM   #12
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Quote:
Originally Posted by eminehart View Post
I have found this to be the very best fix to date as well. Works perfect on stock injectors and aftermarket as well.
Have you collected fuel trim data to see where the resonance has shifted to? I guess the extra flexible hose also absorb some of the pressure pulses.
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Old 12-28-2012, 05:41 PM   #13
eminehart
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Quote:
Originally Posted by Airboy View Post
Have you collected fuel trim data to see where the resonance has shifted to? I guess the extra flexible hose also absorb some of the pressure pulses.
There seems to be some smaller fuel corrections around 3200-3400 but only about 10 percent or so on 1 car. A car with the stock airbox was less.
also a car with id1000s and intake saw no issues and I left the EL Comp pretty flat.
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Old 01-12-2013, 12:45 AM   #14
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Collected some fuel trim data for an 09 STi with ID1000 and the extra hose from the FPR.


The Engine Load Comp MAP tables has been set to "0". The resonance is still there, just shifted in RPM. The peak is now near 3600 and another near 1800rpm.
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Old 01-12-2013, 12:04 PM   #15
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On stock injectors and stock intake i started to see the upper resonance but i didn't datalog that high. I saw 5% correction at 3500 rpm, but I don't drive the car under moderate throttle any higher than that so I didn't worry about it. I also didn't log below 2000 rpm so i guess it could still be there.
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Old 02-09-2013, 10:55 PM   #16
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Added the 3' of fuel line solved 90% of my issues without specific tuning.

I am throwing in fuel rails, FPR, and tuning this week hopefully. But for those of you who don't have the ability to tune right away this solved most of my issues
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Old 02-10-2013, 04:48 PM   #17
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Here is the solution I developed to address it. Same general principle, just allows for a PnP install and for removing the entire factory contraption.



PM me if you like it

Last edited by lancelucas; 02-12-2013 at 02:38 AM.
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Old 02-22-2013, 09:17 PM   #18
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i have been working on this problem for a few weeks now and figured I would share my experience so far.

I have tried the iaperformance kit and had no luck. I then tried to add another damper on the feed line which then gave me 2 dampers on the feed line and had no luck. It was better with 2 dampers but had to add quite a bit to the compensation tables. With all this being said I have left the old style FPR and one damper on the return line. I then went with one damper and the 3' hose and this worked well but didn't like the coiled up hose under the hood. The last think I could think of doing was removing all the dampers on the feed line completely and zeroing out the comp tables. No dampers on the feed line with the old style FPR and old style damper seemed to do the trick, it will still need a very small amount of tweaking of the compensation tables but this is the best and cleanest fix I could come up with. Only other thing I would want to try is a full fuel rail set up but that cost some $$$$.

There is a kit out there by lucas performance concepts which is a kit that removes all dampers and has the old style FPR. I would buy that before an iaperf kit.
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Old 02-22-2013, 11:49 PM   #19
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Are there any side effects to not having any damper in the system? Would you have to run the pump at 100% all the time?
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Old 02-23-2013, 08:29 AM   #20
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I guess that is something I would like to know also. I have one in the return line.
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Old 02-23-2013, 09:31 AM   #21
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Rails are being installed in my 08 STI as we speak. I'll be sure to post up what is done but as of right now this is what we are doing:

Agency Power fuel rail kit (comes with lines and fittings).
-NOTE: we had to order some extra fittings because one of the fittings was tapered on one side which we couldn't use. We opted for a Y fitting off the block which would allow us to evenly distribute the fuel to either rail and not the traditional way of fueling the first rail then the second rail.

Fuel Lab FPR

Then tuning with an Access Port

Agency Power makes the rail kit that you can find for around 300 bucks. Fuel Lab was 170ish I think. Wasn't that bad of an investment since I plan to go more power later anyways... especially if it solves the issues.
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Old 02-23-2013, 10:54 AM   #22
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Awesome, it will be good to know if this works!

http://www.ebay.com/itm/Agency-Power...48a686&vxp=mtr

Is this the kit that you got?
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Old 02-23-2013, 11:01 AM   #23
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Quote:
Originally Posted by Airboy View Post
Are there any side effects to not having any damper in the system? Would you have to run the pump at 100% all the time?
According to theory, yes, the damper serves a well-intended purpose (absorbing fuel line pulsation). This isn't from the pump being run at partial speed, but rather, from injectors opening and closing and such.

http://www.injector.com/cart/pc/Puls...Dampers-c4.htm
http://injector-rehab.com/shop/fpd.html

Here in the real world, our 4 cylinders do perfectly fine with no ill effects without a damper. The OEM dampers don't do a whole lot and are prone to getting noisy anyways, unfortunately.
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Old 02-23-2013, 11:06 AM   #24
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So the damper you posted would be a good alternative to the oem dampers? I also believe that the oem dampers create more noise because of the results that I am seeing.
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Old 02-23-2013, 11:32 AM   #25
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Quote:
Originally Posted by cummins990 View Post
Awesome, it will be good to know if this works!

http://www.ebay.com/itm/Agency-Power...48a686&vxp=mtr

Is this the kit that you got?
Yes. But if you shop around you can find it for cheaper also.
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