The famous stumble...fixed?

anyone find a tune necessary? i see a few people mention the possibility, but not definitive answer.

I have not thus far. Most who do mess with the tune, have 07+ STI/WRX/LGT where they added a fuel comp table, and they adjust or 0 that out. In 05/06 we dont have that.

the Cobb install instructions say "IMPORTANT! Retuning is

HIGHLY suggested to account for the newly corrected fuel system under cruising conditions. "

 

I emailed Dave to check and will pull a LV later today.

^ that is true, however the Cobb kit is also for the 08+ sti that has the fuel comp tables.

damn. after really considering spending the money to do this, I find out that the 07+ topfeed fuel system is "totally" different. this thread, at the moment, is really only relevant to 06 and previous systems...

 

I've got dampers where y'all seem to have your regulator. and my regulator is somewhat built into my hardlines at the manifold. not as simple, but I am going to look into how I could make it work.

 

EDIT: looks like a Turbosmart TS-0402-1001 is needed ($25) to fit where the current regulator is, then similar hoses to connect it up. looks like 1 less quick connect, but 1 threaded fitting for the turbosmart adapter.

Edited November 25, 2014 by Flinkly

so Dave said that tuning doesn't appear to be necessary on the 05/06 cars as they adapt to this change fine. I'll pull a LV later today just to see.

so Dave said that tuning doesn't appear to be necessary on the 05/06 cars as they adapt to this change fine. I'll pull a LV later today just to see.

 

cool, thanks for the info.

If you guys haven't yet, make sure to update the fuel pump duty cycles, since aftermarket pumps seem not to like it.

 

Romraider how to thread: http://www.romraider.com/forum/viewtopic.php?f=34&t=6356

 

STi Mikey Confirmed that it fixed his stumble: http://www.romraider.com/forum/viewtopic.php?p=69216#p69216

I played with the duty cycles. The regulator cant bypass enough fuel at low load driving with the pump at 100%, my fuel pressure is pretty high like that. I talked to DW and they said there pumps are completely fine with the duty cycles as long as its a minimum of 7v if I member correctly.

 

My STI regulator is still working just as I had hoped

Why not run it at 66% at low loads?

 

Glad to know that the pump works fine with factory load limits, I hear Walbro's don't like 33% at all.

I just did this over the last weekend and am happy to report things are operating well.

 

Side note: E85 fixed pretty much all of my stumble but my LV fuel trims still bounce around. I did this to monitor the fuel trims and see if they will stabilize.

yeah, I'm seeing some pretty big learning swings at either end of the spectrum, but waiting for GSTMIC for retune

I just wanted to attach this chart of my "stumble". you can faintly see one at 1200 rpm, and "the" big one at 1700. I have another above 3k, but this data is for fuel injector fine tuning and so I'm mostly after cruise and idle data. I have been going slowly thru the 1700 rpm range to capture this though. No matter what I change for injector tuning, it always tends to be about +10% at it's peak, and is always at 1700. stupid harmonics....

 

For reference, I have a Whalbro pump, DW850 injectors, and OEM fuel components otherwise. And I still have my injector comp tables intact, but adjusted for bigger injectors. I did zero them for a few runs and the stumble continued to exist.

I have an 05 LGT with the same studder stumble between 2200-2500 rpm. I looked at the stock FPR setup, and wonder if I can just replace that with the other Subaru FPR part no. 22670AA351? Do I need to change the fuel lines in the area to use that part? Is it really the FPR change that fixes the studder? I have been custom tuning it with Dave at CryoTune, but we can't get rid of it. Thanks, TurboTwin.

one thing I do want to repeat (for clarification) is that there really isn't an "eliminated stumble" solution, only "reduction" or "moved/shifted" solutions. Does that make sense?

 

so you either reduce the amplitude of the hump/peak/stumble (seems to be what the STI regulator does), or you shift it in the RPM band (left or right, which is what mostly happens with 3 extra feet of fuel line). also, there is and always will be more than one hump, even if you don't notice it. I've found 3 between idle and 4k so far with my car.

 

I can't speak to fixes, as I've not tried anything but ECU tuning (which hasn't worked so far, since it seems to be a physical harmonic inherent in the fueling system).

Edited December 11, 2014 by Flinkly

apologies in advance for the wacky theory, but can any of these harmonics be due to harmonics observed by the MAF? (air rather than fuel, or maybe in addition to fuel). if there are pulsations going through the MAF, it might create some false signals.

 

related to the above, do you have your intake resonator deleted?

 

also, is there anyone running SD that has this issue?

OP - sorry about your car. Was just curious if you used a generic ebay adapter to add in your mechanical fuel gauge? Among all the brands I carry, none have a 5/16" (8mm) barbed fitting with a 1/8NPT port. Lots of different ways to rig it up, but a fitting like this looks the cleanest, and the ebay part is the only one I have found thus far.

 

http://i.ebayimg.com/00/s/NDc3WDcwMA==/z/fDIAAOxyNo9Ss-Tp/$_12.JPG

 

 

Next runner-up is this one, mounted to the rail, with the line coming off it. Only downsides are price and need for a -6AN plug (1/8NPT port is on block opposite -6AN port) . Prefer to minimize potential leaks and not spend ~$50 on the fitting.

 

http://aeromotiveinc.com/wp-content/uploads/2014/01/15120.jpg

Edited December 12, 2014 by Underdog

I am tuned for SD and have this issue. The fuel issues have been constant problem and have plagued me forever - car is down for the winter at the moment but this thread has convinced me to try this as a solution.

 

Thanks. Probably not an "air issue" then, probably fuel like everyone has been saying Back to the thread then

Ok wait. To much information to process.

 

My 08 has this fluctuation/stall at low throttle that I don't know how to get rid of. It only happens when I tap/step on the throttle a little. It's fine in WOT.

 

I've heard different tings it can be

 

-Vacuum leak, (probably not it)

-Fuel pump O-ring.

-etc

 

Is this what you are talking about? I'm looking for a fix for my car too.

can you log it? if you log fuel corrections vs. rpm (and remove non-steady state data), any harmonic inherent in the fuel system will show up clear as day. you'll even learn where it/they happen, and how much your car is having to account for the problem.

 

but since you say yours only happens on light throttle, it almost makes me think your tip-in is off. either way, logging the data and graphing it will show you if you've got harmonics.

 

PM me if you can log and I can assist in parameters and data mining. in all honesty, i'd love to see what your harmonics are, and then see what happens if you replace the regulator (since you've got the same system that I do). If it works for you, I'll be ordering parts after seeing the data.

Edited December 18, 2014 by Flinkly

I wanted to report that I had severe stumbles in the 2000 to 2500 rpm range. I changed the fuel pressure regulator to the 2007 STI setup, and this cured my problem. It is so much smoother, more power all over. I would say it is 90% cured. I will now have a final tune by Dave of cryotune, and let you know the results after that. I wish I had done this change years ago. My car is a 2005 LGT 5spd Wagon, with stock turbo, custom tune, up pipe, downpipe, intake and rebuilt engine with forged pistons. Thanks so much to the people that figured this fuel pressure issue out, and posted it here.

Yeah, I spent a lot of time trying to figure out my issue and finally found the regulator issue. Posted it up hoping it could help others too. Unfortunately I only drove on it for a few weeks before I totaled my car, but hopefully it's a long term fix for some!

I wanted to report that I had severe stumbles in the 2000 to 2500 rpm range. I changed the fuel pressure regulator to the 2007 STI setup, and this cured my problem. It is so much smoother, more power all over. I would say it is 90% cured. I will now have a final tune by Dave of cryotune, and let you know the results after that. I wish I had done this change years ago. My car is a 2005 LGT 5spd Wagon, with stock turbo, custom tune, up pipe, downpipe, intake and rebuilt engine with forged pistons. Thanks so much to the people that figured this fuel pressure issue out, and posted it here.

 

Turbotwin, after you did the regulator swap and before the retune, was there still a flat spot/stumble?

 

I'm asking because initially my stumble was between 2500-3000rpm. Now since I've removed the three stock regulators and installed the IAP FPR kit (http://www.iaperformance.com/product_info.php?products_id=3155) the stumble moved to 2000-2500rpm. Will it go away once it is retuned? I'm hoping that I don't need to keep trouble shooting and buying parts.

After the fuel pressure regulator was swapped to an 07 sti style with new lines, 90% of the problem was gone. There is still a flat spot at just about 2500 rpm, but only at certain part throttle conditions. I have not had the retune done yet, so I still hope that may cure it, but I will let you know. I would say that if you do the FPR and lines, you should reset the ecu after that, to clear any learned 'bad habits' the car had before the change.