The famous stumble...fixed?

I have an 07 5EAT LGT. I do get a pause/hesitation around 1800 - 2500+ rpms when going from a stop. Then the car finally gets going after 2500+ (boost). Not sure if this is legit stutter or just it being a subaru + turbo + 5EAT. Happens more when it's warmed up (heat

soak?)

 

No other hesitation through the rpm range or other gears.

Do you use Techron? If not, put in a full container next time you fill the tank... Techron first. Then after a day or two see if that hesitation is still there. Likely won't be.

Use no substitute "injector cleaner," Techron only.

Got the Turkeylord's tees today! Nice and clean compared to using universal tee's and step downs.

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/Engine/Fueling/FPR/FPR%20Vacuum_002.jpg~original

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/Engine/Fueling/FPR/FPR%20Vacuum_003.jpg~original

I think we need to add a new T to the lineup. Same as is now, but the t'd off nipple should be for 5/32" hose ID. Specific to FPR reference line from BOV reference line hose.

Nahhh no need to, FPR lines are actually fairly thin and are streched to fit by Subaru. If you cut the stretched part it should fit perfectly, but I would just buy a new hose and call it a day. I think I actually used a 5/32" vacuum hose, I use them for my boost gauges so had some spare.

Yeah, when i picked up a foot of new tubing at napa, they only had 5/32. Was looking for 3/16, but it seems to be working fine and is also what i used for my boost guage.

I've also been toying with cleaning my TB to see if that helps at all with smoothing idle.

Overall, the new sti fpr, extra foot of fuel hose, and new fpr reference connection have eliminated the "tip-out" stumble for me, but only moved my harmonics up a few hundred rpm. Win some, lose some.

Oh, and you're right, obviously. The bov line and 5/32 hose both stretched fine over 1/8 inch barbed t's i had from autozone.

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Received my SS 5/32" wye yesterday and plumbed it in. Former FPR feed was 7" of 5/32" hose. Now I have 6" of 3/16" BPV hose to the tee, 9.25" of 5/32" to the wye, and 2" of 5/32" for each branch (boost gauge sensor and FPR). Line volume to the FPR went from ~.043in^3 to ~.121in^3, for what it's worth. At least it is tapped-off the plenum directly after the throttle plate now.

The original FPR source barb on the STI manifold took a 1/8" EPDM cap; 5/32" was too big, and 9/64" was okay, but the 1/8" fit best.

http://imageshack.us/a/img540/3253/6dE8i5.jpg

Haven't driven it yet... :-/

I'm still on my break-in map anyways, as I have only put on ~200 miles since I finished the project in March. Hopefully I can get it calibrated soon. Not very helpful, I know. Posting it more for plumbing information for others.

Yeah, when i picked up a foot of new tubing at napa, they only had 5/32. Was looking for 3/16, but it seems to be working fine and is also what i used for my boost guage.

3/16's might be a little too big for stock FPR. 4.5mm = 0.177", 3/16 = 4.74mm, while 5/32 = 3.96mm. It's better to slightly stretch it so that it doesn't blow off (especially on stock FPR since there is no room for zipties).

Overall, the new sti fpr, extra foot of fuel hose, and new fpr reference connection have eliminated the "tip-out" stumble for me, but only moved my harmonics up a few hundred rpm. Win some, lose some.

 

Oh, and you're right, obviously. The bov line and 5/32 hose both stretched fine over 1/8 inch barbed t's i had from autozone.

 

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That's awesome, I can't wait to get the new FPR and get rid of the mess thats there currently, I might be able to squeeze my fuel filter there too!

I just did 90 miles on new setup, and A learning was at 2.9%, EDIT: I read it wrong it is actually -0.30! This is the lowest it has ever been for me. I've searched for boost leaks, I've replaced the injectors, replaced the fuel filter (via retrofit and bypass), and to have a 5 minute mod fix it .

I think the new FPR will help even more, especially with elimination of crosstalk, heck my fuel pressure might stay up for longer then then couple hours finally.

Do you use Techron? If not, put in a full container next time you fill the tank... Techron first. Then after a day or two see if that hesitation is still there. Likely won't be.

 

Use no substitute "injector cleaner," Techron only.

Thanks. I do use Chevron gas most of the time and switch to Shell every few tanks (91 oct is the highest I can get). I've used a bit of MMO in 2 tanks over the past 6 months. I do have something else going on, possible bad o2 or something I need to sort.

I was wrong this morning, either I looked at the previous log or my A learning changed between my house and gas station. I dont think A learning should change that easily after 90 miles though.

As you can see A learning is in the negative, this is definitely the lowest I've ever seen it be, only my FXT has been this low in A learning (which uses the old style fuel rail attached FPR and only couple inch long vacuum hose).

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/Engine/Fueling/FPR/LW_FPRVacuumChange_90mCity-Aggresive.jpg~original

Looks like a wee bit of latency adjustment and a bump in scalar is in order.

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Keeping the fuel based stuff stock for now, until the car is in tip top shape mechanically. I was gonna try another Fuel Learning Map this week, but this mod tickled my interest, so trying to limit my variables .

Lol, i hear ya. I'm about to tear off some parts to "eliminate" them as variables to solve fueling issues.

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The "fix" has been known for several years. All it really takes is elongating the fuel lines to reduce the "water hammer" effect (what is causing the stumble). Relocating the FPR can help with the really stubborn ones. Subaru even elongated the lines themselves in the 15 STi. We have performed the mod successfully more times than I can recall. That is why we keep 25ft rolls of fuel hose on the shelf, Lol. Good to see you finally got around to doing it yourself.

I'm in the process of tuning with cryotune and have this same stumble. How long do you make the new fuel lines? Do you extend both of the lines that connect to the manifold or just the supply hose? I also read that if you use a bigger size hose you won't need to use a longer hose? Any truth to that? TIA

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I was wrong this morning, either I looked at the previous log or my A learning changed between my house and gas station. I dont think A learning should change that easily after 90 miles though.

 

As you can see A learning is in the negative, this is definitely the lowest I've ever seen it be, only my FXT has been this low in A learning (which uses the old style fuel rail attached FPR and only couple inch long vacuum hose).

 

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/Engine/Fueling/FPR/LW_FPRVacuumChange_90mCity-Aggresive.jpg~original

I've been using the btssm app for a while now. I am viewing the A/B/C/D learning values at all times when I drive. And I can see that these values can change very quickly and very often. For example, when I am idling at a traffic light for 2mn, I can see the A value changing a bit every 5-10 sec or so. No big changes of course, but the value does get updated very often. fyi..

I've been using the btssm app for a while now. I am viewing the A/B/C/D learning values at all times when I drive. And I can see that these values can change very quickly and very often. For example, when I am idling at a traffic light for 2mn, I can see the A value changing a bit every 5-10 sec or so. No big changes of course, but the value does get updated very often. fyi..

I see them changing a lot in the first 30 or so miles, but after that they seem to stabilize a little more. But still that's good to know. I usually try to take learning view screenshots around the same time (right after I pull off the highway to fill up before driving home so that 2 miles city don't mess with them).

All winter I had A learning in 9's, with warmer weather (and post fuel filter bypass/replacement), I've been in 5-6's, now only thing that changed is vacuum source and I'm in negatives to 3%.

...now only thing that changed is vacuum source and I'm in negatives to 3%.

Well I spoke too soon, just pulled a LW and A learning is at 4.50%. Looks like aggressive driving and probably less idling is the reason why it was in the negatives.

Attempting this mod and I cant for life of me get the fuel lines by the strut tower off. I bought a tool but the ridge infront of the plastic quick disconnect wont allow the tool to get under the plastic. Any ideas?

I had the same issue. However I had a cheap plastic tool that I broke in half and slid one side in at a time at an angle. . .piece of cake after that

https://www.amazon.com/dp/B000W0UZHG/ref=cm_sw_r_awd_wRBQvbBSHMKWN

Attempting this mod and I cant for life of me get the fuel lines by the strut tower off. I bought a tool but the ridge infront of the plastic quick disconnect wont allow the tool to get under the plastic. Any ideas?

I had to go buy the cheapo harbor freight plastic quick disconnect tool set. The plastic has enough give to slip it in past the ridge. $6 for a set at the HF.

Had originally boght a single $12 dollar metal tool at napa.

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I'm in the process of tuning with cryotune and have this same stumble. How long do you make the new fuel lines? Do you extend both of the lines that connect to the manifold or just the supply hose? I also read that if you use a bigger size hose you won't need to use a longer hose? Any truth to that? TIA

 

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Supply and return. Using a larger size hose can be dangerous. It tends to lead to leaks.

Fuel filter or pump changed recently? Mine is still present as well but not as pronounced as before. First mod was the fpr (ran good for a week until the ecu learned it back)

Second was spark plugs (previous owner had Tribeca plugs in it )

Then fuel pump and filter (running great but still little hiccups here and there)

Need to tee the bpv line and see how that does. . .

Well new injectors and FPR mod later and my issue is still present. Time for partout I guess.

Tried zero'ing individual ipw comp tables and logging? I think that might be part of my problem; real life fueling no longer matches with stock ipw comp tables. Not that i know much about what i'm talking about.

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