xtea Posted July 8, 2015 Share Posted July 8, 2015 Is this stumble? http://youtu.be/yRmK-Uf26bs Link to comment Share on other sites More sharing options...
SBT Posted July 8, 2015 Share Posted July 8, 2015 When you hold it at steady-state like that, it sounds like uneven tire pressure on your 4 tires (or worse mis-matched tires) unwinding in your center differential. - Pro amore Dei et patriam et populum - Link to comment Share on other sites More sharing options...
covertrussian Posted July 8, 2015 Share Posted July 8, 2015 I noticed there is a lot of crosstalk in the 05 FPR. I was trying to 100% make sure which line was feed and which one was return (FSM couldn't make up it's mind on which one was which) , disconnected both of them from fuel rail and put dry towels under them. Then at the fuel pump blew into the line and saw fuel on both of the towels, just the top line had a little more fuel then bottom line. Also noticed that my fuel pressure would bleed off fairly quickly (within couple hours). Tempted to try the old style FPR, much simpler and cleaner (esp with in engine bay fuel filter). 05 LGT 16G 14psi 290whp/30mpg (SOLD) 12 OBP Stock 130whp/27mpg@87 Oct 00 G20t GT28r 10psi 250whp/36mpg 22 Ascent STOCK Link to comment Share on other sites More sharing options...
heiche Posted July 8, 2015 Share Posted July 8, 2015 Yeah i believe the top line (top at the firewall AND top line at the intake manifold) is the feed, and the bottom line is the return. At least on my 05 anyway. And the FPR gets plumbed into the return line, like the pics in post #1. BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT Link to comment Share on other sites More sharing options...
covertrussian Posted July 8, 2015 Share Posted July 8, 2015 Yup correct, that's what I saw too and attached the in bay fuel filter to the top line. $100 for oem non adjustable fuel pressure regulator? I might see if I can score a Nismo adjustable one or just go aftermarket adjustable. 05 LGT 16G 14psi 290whp/30mpg (SOLD) 12 OBP Stock 130whp/27mpg@87 Oct 00 G20t GT28r 10psi 250whp/36mpg 22 Ascent STOCK Link to comment Share on other sites More sharing options...
rhino6303 Posted July 8, 2015 Share Posted July 8, 2015 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. Link to comment Share on other sites More sharing options...
covertrussian Posted July 8, 2015 Share Posted July 8, 2015 That makes sense, especially if your AVCS is lagging on one of the heads. 05 LGT 16G 14psi 290whp/30mpg (SOLD) 12 OBP Stock 130whp/27mpg@87 Oct 00 G20t GT28r 10psi 250whp/36mpg 22 Ascent STOCK Link to comment Share on other sites More sharing options...
Flinkly Posted July 8, 2015 Share Posted July 8, 2015 (edited) good idea (Cobb's updated fix). Well, the gist of my "fix" is that it didn't fix my harmonics. I ended up adding ~18 inches more of line, plus the STI FPR (added the extra line cause the damn GS MC Brace was in the FPR's way. useless part, need to tear it out and sell it to some newb). It did APPEAR to literally quiet up my engine as well as moved my harmonics and lower them a few percent of correction (lets say +10% down to +7%). I'll admit I'm at my wit's end trying to fight with my fueling issues. more logging to come. Edited July 8, 2015 by Flinkly * Build Thread * 26.53 MPG - 12 month Average * Link to comment Share on other sites More sharing options...
Flinkly Posted July 8, 2015 Share Posted July 8, 2015 (edited) a thought I keep having: Could AVCS cause increased correction, because air is flowing thru the cylinder and out at high AVCS angles? Edited July 8, 2015 by Flinkly * Build Thread * 26.53 MPG - 12 month Average * Link to comment Share on other sites More sharing options...
covertrussian Posted July 8, 2015 Share Posted July 8, 2015 It's possible, AVCS changes VE, which would change AFR's. I'm also seeing ambient temperatures change my learning correction amount for idle. In April my A learning was in ~9% (post in tank fuel filter bypass), yesterday it was ~5%. 05 LGT 16G 14psi 290whp/30mpg (SOLD) 12 OBP Stock 130whp/27mpg@87 Oct 00 G20t GT28r 10psi 250whp/36mpg 22 Ascent STOCK Link to comment Share on other sites More sharing options...
Flinkly Posted July 8, 2015 Share Posted July 8, 2015 While it might not be the most exciting tune ever, could I set AVCS at 0 or 10 and do logging (no boost) from idle to 3k without harm? might cause more noise from load comp. tables or IPW comp. tables though, not that either is very accurate anymore anyways. * Build Thread * 26.53 MPG - 12 month Average * Link to comment Share on other sites More sharing options...
covertrussian Posted July 8, 2015 Share Posted July 8, 2015 Yup, you can zero out the whole map if you want for testing! Oem tune just does that for highway driving, which is where I found most of the MPG gains (setting it to 10 from 0). http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/AVCS/05LGTStockAVCS.png~original 05 LGT 16G 14psi 290whp/30mpg (SOLD) 12 OBP Stock 130whp/27mpg@87 Oct 00 G20t GT28r 10psi 250whp/36mpg 22 Ascent STOCK Link to comment Share on other sites More sharing options...
xtea Posted July 8, 2015 Share Posted July 8, 2015 Is this stumble? http://youtu.be/yRmK-Uf26bs When you hold it at steady-state like that, it sounds like uneven tire pressure on your 4 tires (or worse mis-matched tires) unwinding in your center differential. I am not very smart, are you saying this is stumble? The tires are fine. This started happening at 2500 rpms after going stage 3 with a new fuel pump. Link to comment Share on other sites More sharing options...
FJuan Posted July 8, 2015 Share Posted July 8, 2015 I am not very smart, are you saying this is stumble? The tires are fine. This started happening at 2500 rpms after going stage 3 with a new fuel pump. What he's saying is that is not the normal stumble. The normal stumble happens between 2 - 3k RPMs, while you are accelerating (not crusing), it almost feels like the car is misfiring. Some say it's a surge and some say stumble. Once the RPMs are above 3k, then the car feels good My wife's balls are delicious. Link to comment Share on other sites More sharing options...
whitrzac Posted July 8, 2015 Share Posted July 8, 2015 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. Mr spank? Seems like it would do something similar to adding more line to the setup. Link to comment Share on other sites More sharing options...
xtea Posted July 9, 2015 Share Posted July 9, 2015 What he's saying is that is not the normal stumble. The normal stumble happens between 2 - 3k RPMs, while you are accelerating (not crusing), it almost feels like the car is misfiring. Some say it's a surge and some say stumble. Once the RPMs are above 3k, then the car feels good Yeah mine happens at low contant throttle in the 2200-2600 range. Link to comment Share on other sites More sharing options...
heiche Posted July 9, 2015 Share Posted July 9, 2015 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. ^ this is cool BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT Link to comment Share on other sites More sharing options...
FJuan Posted July 9, 2015 Share Posted July 9, 2015 Yeah mine happens at low contant throttle in the 2200-2600 range. Have you pulled a data log to see what's going on? Otherwise, SBT's post sounds more of what's going on. My wife's balls are delicious. Link to comment Share on other sites More sharing options...
xtea Posted July 9, 2015 Share Posted July 9, 2015 Have you pulled a data log to see what's going on? Otherwise, SBT's post sounds more of what's going on. What should i log? I dont think its tire related, it feels more like the throttle is bouncing as if you just came off the gas quick in low rpm. Link to comment Share on other sites More sharing options...
SBT Posted July 9, 2015 Share Posted July 9, 2015 ^ 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. - Pro amore Dei et patriam et populum - Link to comment Share on other sites More sharing options...
m sprank Posted July 9, 2015 Share Posted July 9, 2015 I see my name mentioned, but so many threads, I get lost (old age creeping in). The standard "stumble" is related to a "water hammer" effect. Lengthening the lines and removing the FPR from the hard mount has fixed the issue in all the cars we encountered it. Normally just lengthening the lines does the trick. Subaru has used a single manifold runner for boost reference to the FPR for ever. I am not a fan of teeing into the BPV manifold reference hose because it seems everyone else does already (like for a boost gauge). Many times we have seen so many tees off the BPV that the BPV does not get enough volume of air to work properly. Then people start swapping BPV's for no good reason. Link to comment Share on other sites More sharing options...
covertrussian Posted July 9, 2015 Share Posted July 9, 2015 ^ this is cool THANK YOU! I was trying to find this post and gave up. That post has been VERY informational. Especially the Youtube video that they posted. Cliff Notes: Rubber fuel lines are good, they absorb certain pulsation frequencies, and reduce the need for a fuel damper. This could be why adding a foot of fuel hose helps with the stumble, more hose more dampening of the pulsations.Keep your FPR vacuum lines short, the longer they are the more likely they are to cause resonance in fuel pressures. Key point 2 is the bigger key here, where the video takes about pulsations through tubes in a similar fashion as a pipe organ. At 5:40 he posts an interesting chart of hose lengths and rpm's they would resonate at for 4, 6, and 8 cyl engines. If you look at the graph, the shorter the vacuum hose the higher the resonance RPM is, the goal is to keep the hose so short that you never hit the resonance RPM. Our main issue is using only one cylinders vacuum for FPR feed, but by switching to BOV vacuum line, we are also increasing the vacuum hoses length. The stock FPR vacuum line is about 4.5mm ID and is about 8-10" long. BOV vacuum line is 7mm ID, about 19" long (rough measurements with my tape measure) and is teed into already (infamous blue tee). On a bright side BOV line to FPR line would be only about 4-5" long , but I don't think we can dismiss the 19" of resonance form the BOV line. Our motors don't make it easy to make a short FPR vacuum feed, even if we drill and tap the plenum, the hose would be at least 14", but it would be a smaller hose (4.5mm instead of 7mm) though I wonder how much of a difference it would make in resonance. 05 LGT 16G 14psi 290whp/30mpg (SOLD) 12 OBP Stock 130whp/27mpg@87 Oct 00 G20t GT28r 10psi 250whp/36mpg 22 Ascent STOCK Link to comment Share on other sites More sharing options...
xtea Posted July 9, 2015 Share Posted July 9, 2015 So is the 07 sti FPR a waste of money? Longer hoses solve the problem and thats it? Link to comment Share on other sites More sharing options...
covertrussian Posted July 9, 2015 Share Posted July 9, 2015 (edited) So is the 07 sti FPR a waste of money? Longer hoses solve the problem and thats it? No it could still help. Cobb did their testing on a newer WRX/STI's (08+) which are still different then what Legacy's have (at least 05-06 ones do). I think converting to 04-07 FPR is still a good idea and switching the FPR vacuum feed from a single cylinder to the plenum is still a must. I'm trying to find a better alternative to the BOV line now. Edited July 9, 2015 by covertrussian Got the hoses that he was talking about mixed up 05 LGT 16G 14psi 290whp/30mpg (SOLD) 12 OBP Stock 130whp/27mpg@87 Oct 00 G20t GT28r 10psi 250whp/36mpg 22 Ascent STOCK Link to comment Share on other sites More sharing options...
Flinkly Posted July 9, 2015 Share Posted July 9, 2015 Want to be at least post-turbo/compressor. Not alot of options. I do have my boost line t'd to that already, and that hose is redic long. Could get a t that splits of as 4.5mm, with a main body of 7/9mm. Turkeylord! Sent from my XT1028 * Build Thread * 26.53 MPG - 12 month Average * Link to comment Share on other sites More sharing options...
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