BigTDogg MA Posted June 20, 2017 Share Posted June 20, 2017 Issue: At partial throttle, I get a hesitation where the engine speed varies about 300 RPM centered around 2800 RPM or so. Background Info: • This has been happening for a while, since before this newest engine • Only happens on partial throttle, no hesitation at WOT or even just a higher accelerator % • The car has recently had the following components replaced (all Subaru OEM): o MAF o Throttle Body o Coil packs and spark plugs • Injectors replaced with 21k mile STI injectors at 149k miles (202k on car now, so total of 74k on injectors) • DW65C pump installed 55k miles ago • New OEM front O2 sensor 25k miles ago • STI style regulator installed 25k miles ago I can log any parameters desired, as I've got RomRaider. Below is a chart I plotted showing accelerator pedal angle being held constant (black line) and the variation of various sensors. The engine speed variation is shown to be very subtle due to the y-axis scale, but it varies 314 RPM with 0 change in accelerator pedal input. I've attached the Excel file for reference as well. Any insight is greatly appreciated!Engine Log 6-12-2017.csv Link to comment Share on other sites More sharing options...
Max Capacity Posted June 20, 2017 Share Posted June 20, 2017 I suggest you send that to Mike at http://www.tuningalliance.com and see what he thinks. 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
08Legacy-GT Posted June 20, 2017 Share Posted June 20, 2017 I suggest you send that to Mike at http://www.tuningalliance.com and see what he thinks. second this ^ 2017 Subaru STI 2008 Subaru Legacy 2.5i limited Link to comment Share on other sites More sharing options...
compsurge Posted June 20, 2017 Share Posted June 20, 2017 What is your feedback knock and Learning View in that load/rpm cell? Link to comment Share on other sites More sharing options...
BigTDogg MA Posted June 21, 2017 Author Share Posted June 21, 2017 I'll check the LV feedback knock and report back. Thanks for the suggestion Max, I've sent the file to my mechanic and my tuner already. I'm just looking to get another set of eyes on it. Link to comment Share on other sites More sharing options...
compsurge Posted June 21, 2017 Share Posted June 21, 2017 It sounds a lot like what my car has done for the past 90k. I gave up a while ago trying to fix it. I'll convert this car to electric before I can figure out what the root cause is. If you fix it, let me know! One thing that may fix the issue is the fuel pump rewiring. Link to comment Share on other sites More sharing options...
Slammed05 Posted June 21, 2017 Share Posted June 21, 2017 Sounds kinda like the hesitation I have and have replaced everything you said as well almost to a T Mine seems to be a but lower though more around 2500ish, but I'll get like a sputtering/bucking almost And if I give it more gas, car will still build boost, a/f still richen up, but ya the car like won't move, I usually end up backing off the gas, and then slowly start giving it gas and it'll kinda clear itself up Link to comment Share on other sites More sharing options...
Max Capacity Posted June 21, 2017 Share Posted June 21, 2017 Just saying, my wagon doesn't do this, I remember during one of the street tune's, talking with Mike about basically this issue, he took care if it. www.tuningalliance.com 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
Pazuzu Posted June 22, 2017 Share Posted June 22, 2017 Hoping my tuner can work mine out as well..... i got fresh plugs, engine, fuel pump, injectors, basically everything under the hood except maf, map, and coils..... I also wondered about the fuel pump rewire. A lot of guys had good luck adding the foot or so of rubber hose. This is the emphasis subaru stumble and that has been the fix the most people have had luck with. Some people, including myself have noticed changing your fpr hose from the side port to the three way in the back. Sent from my SM-G930P using Tapatalk Link to comment Share on other sites More sharing options...
Th3Franz Posted June 22, 2017 Share Posted June 22, 2017 engine load compensation table may help with this. Also try bumping up the minimum fuel pump duty cycle. -Franz The end of a Legacy http://www.youtube.com/th3franz Link to comment Share on other sites More sharing options...
dga Posted June 22, 2017 Share Posted June 22, 2017 Got the same issue from about 2500 - 3500 RPM. I logged it, but still need to take a look at the logs. This was not an issue before, but then I went with the DW fuel pump and DW1000cc injectors, to tune the 16G that was on the car to it's full potential, then it slowly started cropping up. Now it's ever present at any throttle application; from mild to wild. I was going to convert the car to a parallel fuel rail set up and aftermarket FPR to see if the hesitation is due to the fueling. Link to comment Share on other sites More sharing options...
BigTDogg MA Posted June 23, 2017 Author Share Posted June 23, 2017 Got the same issue from about 2500 - 3500 RPM. I logged it, but still need to take a look at the logs. This was not an issue before, but then I went with the DW fuel pump and DW1000cc injectors, to tune the 16G that was on the car to it's full potential, then it slowly started cropping up. Now it's ever present at any throttle application; from mild to wild. I was going to convert the car to a parallel fuel rail set up and aftermarket FPR to see if the hesitation is due to the fueling. I should also note I have parallel feed rails, with the STi regulator and DW65C pump. Link to comment Share on other sites More sharing options...
dga Posted June 23, 2017 Share Posted June 23, 2017 Well damn... Link to comment Share on other sites More sharing options...
Slammed05 Posted June 24, 2017 Share Posted June 24, 2017 I'm getting my car tuned open source tommarow, and am hoping that it's either somewere in the tune that he can fix, or at least lead me in some sort of direction on what it is But mine doesn't do it all the time, it's completely random But the more and more I search for this no one, on this forum and others have found any sort of solution Link to comment Share on other sites More sharing options...
compsurge Posted June 24, 2017 Share Posted June 24, 2017 I'm getting my car tuned open source tommarow, and am hoping that it's either somewere in the tune that he can fix, or at least lead me in some sort of direction on what it is But mine doesn't do it all the time, it's completely random But the more and more I search for this no one, on this forum and others have found any sort of solution In my experience, it has been related to low-load "knock". If the car really bucks at low throttle, it's likely timing being pulled. If you examine your learning view and datalog knock count in that area, it will add very quickly. There are a few theories such as ringlands that have broken, but not separated, clutch and flywheel engagement on shifting causing false readings, leaking fuel injectors, insufficient fueling (FPR or low voltage at the pump), and small air leaks. I gave up a while ago as I've tried to figure it out over the past 90k miles. I will likely try the STI FPR and bench test the injectors with an Arduino and MOSFET to see how they flow. Link to comment Share on other sites More sharing options...
Slammed05 Posted June 24, 2017 Share Posted June 24, 2017 Well there was 0 learned knock on my car I have been told my Injectors/fuel pump/fueling in general is showing exactly what it should I've already done the sti fpr and vacuum hose re route We could not replicate it, so nothing really came of it Link to comment Share on other sites More sharing options...
dga Posted June 26, 2017 Share Posted June 26, 2017 Cleaned the MAF and reset the ECU and the car is back to being butter smooth at all RPMs. The idle is still a bit off as the ECU is learning, but it does this every time though. If it comes back, I'm guessing I've got something else going on. Link to comment Share on other sites More sharing options...
Slammed05 Posted June 27, 2017 Share Posted June 27, 2017 Man I wish mine was the maf, but I've cleaned it multiple times and never did anything Link to comment Share on other sites More sharing options...
compsurge Posted June 27, 2017 Share Posted June 27, 2017 Man I wish mine was the maf, but I've cleaned it multiple times and never did anything It's more likely due to the fact the ECU was reset. Link to comment Share on other sites More sharing options...
solidxsnake Posted June 27, 2017 Share Posted June 27, 2017 If your load is under 1.3g/rev when this is happening -- which is more than likely, IMO -- then learned knock correction is not active (unless you've played with the knock correction tables). If it's between 0.8-1.2g/rev, then it could be feedback knock. That said, I think the issue is much more likely fueling related. Link to comment Share on other sites More sharing options...
Slammed05 Posted June 28, 2017 Share Posted June 28, 2017 So what exactly does that mean, if there is some sort of knock, doesn't that usually end up meaning motor is junk? Link to comment Share on other sites More sharing options...
Slammed05 Posted June 28, 2017 Share Posted June 28, 2017 And how exactly are you suppose to be able to tell, on my car my engines only got like 60k on it, and good compression Link to comment Share on other sites More sharing options...
solidxsnake Posted June 28, 2017 Share Posted June 28, 2017 So what exactly does that mean, if there is some sort of knock, doesn't that usually end up meaning motor is junk? No. The engine is noisy at lower RPMs, and sometimes that can trigger the knock sensor to believe there's actual detonation occurring when there is none (false knock). That said, the car could actually be detonating, but at low loads and RPMs, a little bit of detonation won't damage the engine. Not saying it's beneficial, but it's not like a little bit of knocking at low loads will promptly destroy a ringland Link to comment Share on other sites More sharing options...
Slammed05 Posted June 28, 2017 Share Posted June 28, 2017 Well that's good to know! I've searched for multiple types of symptoms like this thread, and I've never found a answer, the threads always kinda die out without any sort of conclusion Link to comment Share on other sites More sharing options...
compsurge Posted June 28, 2017 Share Posted June 28, 2017 I think most just live with it versus throwing money at it. At least that's my experience! Link to comment Share on other sites More sharing options...
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