The famous stumble...fixed?

^ Alternatively, you could also have worn half-shafts which would cause that sound and that behavior. I lean more toward my previous assessment though, given what I could hear in your vid. It's definitely not stumble as defined here, sounds more mechanical.

I think it might be mechanical. I wish there was a way for me to determine it specifically though.

Edit: Actually the problem arose after installing stage 3 parts, not before. Have not driven the car hard at all, still in wastegate tune.

Turkeylord!

Yes Turkeylord tee is a must! If you do this and still have the blue TEE, it can come off or leak and give you major AFR issues (lean).

Has anyone seen Cobb's new "fix" posted on nasioc? Essentially they tee in the fpr to the bpv hose rather than the plenum itself so all cylinders are utilized in the vacuum signal.

Tried the above mod today and it definitely made a positive change. I suppose it could be placebo effect, but cruising feels less nervous/twitchy, and idle is also totally smooth now - perhaps for the first time ever. Basically you take your vac signal line from your FPR, and relocate it from the #4 intake runner to a new tee in the BPV line. Cap the now-unused port on the runner. That's it. It goes from a pulsing vac signal from mainly just one cylinder (which tells the FPR to create pulsing fuel pressure) to a much smoother vac signal from the plenum shared by all four cylinders.

I'd definitely suggest to everyone the above easy/free mod and replacing your 05/06 FPR with an 07 STi FPR And no need for coils of extra fuel hose to mask this issue.

Tried the above mod today and it definitely made a positive change. I suppose it could be placebo effect, but cruising feels less nervous/twitchy, and idle is also totally smooth now - perhaps for the first time ever. Basically you take your vac signal line from your FPR, and relocate it from the #4 intake runner to a new tee in the BPV line. That's it. It goes from a spiky vac signal (which tells the FPR to create spiky fuel pressure) from mainly just one cylinder to a much smoother vac signal from the plenum shared by all four cylinders.

 

I'd definitely suggest to everyone the above easy/free mod and replacing your 05/06 FPR with an 07 STi FPR

Picture of set up?

Sure!

Some of it might be hard to see. There's an AEM fuel pressure sensor wired to a TGV input that's partially blocking the view of the new vac line going to the FPR.

Does mileage matter on these FPRs? Can I just snag a used one?

I'd think that you could try a used one.

Sure!

 

Some of it might be hard to see. There's an AEM fuel pressure sensor wired to a TGV input that's partially blocking the view of the new vac line going to the FPR.

you should rotate that sh*t over. or at least that's the way I roll. FPR nipple facing the engine rather than the tower.

Not to say that i'm perfect. my FPR is just sitting in free space. couldn't mount it where I was going to due to useless MCBrace.

Also, was thinking on the roll into work this morning, if AVCS is/can effect fueling by letting air thru during major overlap, it could just as well be affecting the pressure/vacuum that the FPR is seeing being so close to cylinder 4 intake. +1 for moving to BOV line.

Does mileage matter on these FPRs? Can I just snag a used one?

Get a used 2005 one, maybe even two just to be safe. I just bought one at Nasioc for $20 shipped. I have a few more members PM me with theirs too. If you guys have Nasioc accounts I can tell you who to PM.

Also, was thinking on the roll into work this morning, if AVCS is/can effect fueling by letting air thru during major overlap, it could just as well be affecting the pressure/vacuum that the FPR is seeing being so close to cylinder 4 intake. +1 for moving to BOV line.

This makes me wonder and thing if this is another reason why my car would not like running 20*+ of AVCS, it would rob it of fuel pressure basically.

I'm gonna wire in my boost gauge to the 4th cylinder (I've had it at the stock map sensor line for a while now). I'm curious to see how the boost ratings will vary now. Looks like I got a project for today

Tried the above mod today and it definitely made a positive change. I suppose it could be placebo effect, but cruising feels less nervous/twitchy, and idle is also totally smooth now - perhaps for the first time ever. Basically you take your vac signal line from your FPR, and relocate it from the #4 intake runner to a new tee in the BPV line. Cap the now-unused port on the runner. That's it. It goes from a pulsing vac signal from mainly just one cylinder (which tells the FPR to create pulsing fuel pressure) to a much smoother vac signal from the plenum shared by all four cylinders.

 

I'd definitely suggest to everyone the above easy/free mod and replacing your 05/06 FPR with an 07 STi FPR And no need for coils of extra fuel hose to mask this issue.

1) worth doing the mod with stock FPR? Not really comfortable messing with fuel lines

2) where is the stock FPR? driver's side or passenger side?

I've already tee'd my BPV hose for my boost gauge - I guess if I try this, I should try to shorten my boost gauge hose as much as possible (it has 10-12" of slack in it at this point).

Will also look at making the fuel pump duty cycle adjustment (noisy walbro). Another fun project to add to the list

1) worth doing the mod with stock FPR? Not really comfortable messing with fuel lines

2) where is the stock FPR? driver's side or passenger side?

 

I've already tee'd my BPV hose for my boost gauge - I guess if I try this, I should try to shorten my boost gauge hose as much as possible (it has 10-12" of slack in it at this point).

 

Will also look at making the fuel pump duty cycle adjustment (noisy walbro). Another fun project to add to the list

drivers side. between fuse box and brake cylinder, unless 07-09, then on drivers side between intake runners.

i'd do the new reference line for cleaner idle and new FPR or more hose for stumble at speed.

IMO, I think the reference line change is likely to only improve idle, as I can't imagine the noise causing too much issue at non-idle. non-idle issues i'd guess are most likely caused by something else (not to say that a rough idle couldn't be caused by things other than reference line).

IMO, I think the reference line change is likely to only improve idle, as I can't imagine the noise causing too much issue at non-idle. non-idle issues i'd guess are most likely caused by something else (not to say that a rough idle couldn't be caused by things other than reference line).

I was surprised to see on the cobb post that even under WOT the fuel pressure itself was pulsing rapidly with stock FPR signal line routing. I didn't think the FPR could be that responsive! (presumably reacting in a cycle every 2 revs based on the signal line going to mainly one cylinder) See the graph "Initial Test - Fuel Pressure".

Then after the mod, the amplitude of the fuel pressure pulses looks like less than half of what it was as stock - that's the improvement right there. See the graph "Fuel Pressure Graph, Plenum FPR Reference Test".

Crazy stuff.

When I was plumbing in my 07 STI FPR during my 08+ STI swap I had the same thought, that taking the signal from one runner could have an effect. After all, runner length is tuned to account for resonance of the air charge at specific speeds, which is why the N/A long runner manifold generally yields better flow numbers than the STI manifold. Many thanks to the guys at Cobb for digging deeper into it. Looks like I will have to switch the plumbing. Fortunately I am already teed into my BPV line (with a TL SS Tee) and my Defi pressure sensor is already located right next to the FPR. Might just tee off the line to the pressure sensor for minimal added hose length.

P.S. In this pic you can see the barbed fitting I mentioned earlier in this thread to give me a 1/8 NPT bung for mounting the AEM fuel pressure sensor. Worked great after grinding down the lip on the "barb" a bit to fit the Gates fuel hose.

http://imageshack.us/a/img903/1479/mKnqLW.jpg

Fortunately I am already teed into my BPV line (with a TL SS Tee) and my Defi pressure sensor is already located right next to the FPR. Might just tee off the line to the pressure sensor for minimal added hose length.

Ok, that's the 2nd mention of the TL "blue tee". I have the TL tee, just haven't installed it yet - I have a bunch of car stuff to do this summer, after I finish with the garage remodeling, like install the GS TMIC, check all vacuum hoses, install CNT DP, AVO turbo inlet, intake manifold gaskets, etc. For now, she runs

Back to my question: are we tapping the hose(s) involved in the blue tee UNDER the TMIC to provide a new reference input for the FPR? If so, what's the best approach to "tee-ing the tee"? I have some generic vacuum adapters, which might work, but then I might have the same issue the TL tee is meant to address, right?

Or are we tapping the output of the BPV, which, if I'm right, is the one I tapped (comes out of the BPV heading in the general direction of the battery) as input to my gt-digboost20 pressure gauge? Sounds like it's the former, so that my post-BPV pressure gauge is irrelevant.

I haven't studied everything in detail (wish I could, just don't have as much time as I would like), so I understand the general operation of the major components, but am not sure on exactly where every line comes from/goes to. Thanks for all the hard work of everyone here.

hadvw:

The original purpose of the TL SS tee was to replace the blue one in the back of the LGT manifold. It can also be used to add a boost reference point, as shown in my pic above, in the BPV signal line (you can't really see the tee as the STI BPV signal hose comes towards the camera and back over the tee, obstructing the view). Tapping off the BPV signal line is fine in theory, but you want to minimize the draw (volume of air) to maintain BPV and FPR responsiveness/accuracy (what m sprank said earlier).

Great idea on using the turkeylord tee! I should have used my blue one for testing instead of 1/4" lowes tee then another a 1/4" to ~.17" adapter.

I did this mod to my stock 05 LGT FPR setup, so far the car is driving pretty well, did a few logs before and after the mod. AFR's were fairly inconsistent between the logs (before the mod and even after).

After 10 miles learning views are looking pretty good, idle is still at 5% learning but B and C is a 1% or less! But 10 miles is not enough to really tell, thus I'll drive about 60 more miles before I really get my hopes up .

IMO, I think the reference line change is likely to only improve idle, as I can't imagine the noise causing too much issue at non-idle. non-idle issues i'd guess are most likely caused by something else (not to say that a rough idle couldn't be caused by things other than reference line).

It should help everywhere, due to AVCS and intake manifold runner resonances & flow inconsistencies (it's really hard to build a manifold that delivers the same amount of flow to each cylinder).

On a side note...

So I have two obxts where one is a basic stage 1 and the other stage 2+. With the former, you can clearly feel this stumble issue. VERY annoying, while with the latter, nothing at all! Now the stage 2 car has a boost gauge installed where a tee has been placed along the bpv line. So is that helping somehow ??

The stage 1 car is an 05 and has no mods except for a LWCP.

The stage 2 car has a catless up, catted hiflow dp, stromung catback, avo intercooler, LWCP, excedy clutch, wrx flywheel, and an EBCS. But fueling components are all stock as far as I can tell.

Thoughts?

It should help everywhere, due to AVCS and intake manifold runner resonances & flow inconsistencies (it's really hard to build a manifold that delivers the same amount of flow to each cylinder).

yeah, it'll help everywhere, but the biggest impact will be with cleaner idle due to lower fuel harmonics at such low IPW (low quantity of fuel [requested] vs. "large" fuel oscillation noise).

at load, the additional noise isn't preferred, but if fueling is properly tuned, should only cause oscillation around zero, and compared to the amount of fuel requested, should have lower impact on roughness or incorrect fueling.

I mean, at load, this shouldn't be fixing any fueling corrections that don't oscillate around zero. I guess i'm thinking of my fueling harmonics that cause +5% and +10% humps in my fueling correction vs. RPM.

so overall, yeah it should be better than before, but I would expect the most impact being a cleaner/smoother idle. followed by just a less noisy fueling correction across the board.

I think i'll:

1. redo my reference to the BOV line
   
2. log
   
3. zero my load comp and IPW comp tables again
   
4. log
   

and see what happens to my remaining harmonics. cause they still exist, but can't find a correlation to any causes yet, except that they seem to line up well to RPM, and they did move with the new FPR and additional hose length (can't really tell if they moved to lower or higher RPM, cause they happen at "regular" intervals. I think it got a little higher 1.7k -> 2.1k for one). that points me towards fuel harmonics, but I can't figure out what's causing them. ECU? FPR? Exhaust? Intake? AVCS? ugh....

Maybe if I give her a good wash and new tires she'll love me again and just start to behave better.

Feelin' the love in here.

2 more tees on the way to covertrussian, and for the record they are nickel plated brass construction.

Feelin' the love in here.

 

2 more tees on the way to covertrussian, and for the record they are nickel plated brass construction.

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.

Also, i just redid my layout of hoses. Didn't have a nipple or screw to plug the original FPR port, so put it into a T and made a little circle. Reference taken right at BPV, and took the extra length out of my boost guage line.

Car still works, but so far can't butt-sense the change yet. More logging to come.

Sent from my XT1028

I think idle is slightly better, but still not as smooth as it should be. It did help reduce a hesitation I've been having lately, but didn't completely eliminate it.

Here are some learning view numbers:

Stock FPR vacuum: 180 City Miles

0 -< 5.60 = 4.80

5.60 - < 10.00 = 0.40

10.00 -< 80.00 = -4.90

80+ = 0.00

After bypass mod: 45 city miles

0 -< 5.60 = 2.50

5.60 - < 10.00 = -0.10

10.00 -< 80.00 = -2.10

80+ = 0.00

I'll drive probably another 30-40 miles, which is around 1/4th tank and around the time I fillup anyway. I plan on doing a highway trip too, then once I get my 05 STI FPR I'll do this all over again.

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.