The Stumble/Stutter Thread

[m sprank]

try drinking your beer with a coiled up long section of hose - should help the stumble/stutter

 

 

Maybe a funnel too, LOL. But never soap. Bad for intercoolers and beer. :lol:

[mwiener2]

Close the thread!!!!!!!!!!!!!!!!!!!!!!!!

[GearJamr]

On 8/2/2020 at 12:34 PM, Max Capacity said:

I thought I posted these here before, to fix my stumble between 2400- 3000rpm I "T" the line off #4 intake manifold runner into the hose off the blow off valve. That hose sends a signal to the fuel pressure regulator.

 

Reset the ecu and drive the car.

 

 

 

The next picture shows stock set up. I took these photo's years ago,

 

@Max Capacity Do you have a parts list of what you used for this?  Looks like a brass plumbing T (1/4"?) and some zip ties?  Does anything need to be done where the old runner connection is?  Would it be a little easier to use worm clamps instead of zip ties (for needing to remove the intercooler in the future)?

[Max Capacity]

2 hours ago, GearJamr said:

@Max Capacity Do you have a parts list of what you used for this?  Looks like a brass plumbing T (1/4"?) and some zip ties?  Does anything need to be done where the old runner connection is?  Would it be a little easier to use worm clamps instead of zip ties (for needing to remove the intercooler in the future)?

Yes, a brass T from the local hardware store. You can find barb style T's if you look around. https://www.google.com/search?q=brass+barb+style+t+fitting&rlz=1C1OKWM_enUS906US906&oq=brass+barb+style+T+&aqs=chrome.1.69i57j33i160l2j33i299j33i22i29i30l2j33i15i22i29i30l2j33i22i29i30.12414j0j15&sourceid=chrome&ie=UTF-8

Yes screw type clamps will work. Notice on my wagon, Aluminum color tmic, there's no zip tie there at BOV. That car dynoed at 21psi.

Nothing needs to be done to the car's nipples.

[Dillon]

I FIXED MY STUMBLE! (Hesitation, stutter, hiccup after shifting (MT), rough acceleration.

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both: Initially only at steady throttle around 2k-2.5k RPM as a light bucking/stumble/surge of power loss. Then became evident in a wider RPM range and throttle input, along with a loss of smooth acceleration.

MODS

Intake: Stock airbox with K&N panel filter and silicone turbo inlet. REV9 TMIC with silicon throttle body inlet. Crawford AOS.

Exhaust: No name turbo-back. Gutted up-pipe.

Fuel: TREperformance 255lph fuel pump. K&N inline filter. Stock fuel rails ran in parallel. AUS 750cc injectors. Fuelab universal FPR.

Turbo: BNR 16g with billet compressor wheel.

Engine Management: Stock ECM with Cobb accessport.

Tuner and revision of tune(if you don't mind): Stephen Clark at iaTUNING 

MAINTENANCE: 5w40 euro oil. 

Sensors changed: AVCS oil control valve solenoids, crank sensor, cam sensor, MAF sensor, throttle body, accelerator pedal assembly, knock senor location.

Plugs changed: 1 step colder ngk's.

Coil Packs changed: YES, a few times and even bench tested them to check the KV output.

OTHER SYMPTOMS: Occasionally had a very low idle. Happened more often if the ECM was reset.

Check Engine Light: No. Not even when I actually had an AVCS OCV that the ECM didn't like and would stop modulating it. Unplugged it and plugged it back in while holding the RPM around 2.5k and it would momentarily work again for a few seconds.

Etc: I always use premium gas. I tried all the top tier gas stations. Switched back to a paper air filter. Grounded the engine. Hooked up the FPR to the BPV/BOV hose. Preformed the .16 cent BPV mod. Smoke tested multiple times. Countless hours testing a researching. Thought about selling the car, alot. This issue has been present for at least the last 5 years.

RESULTS

What has and hasn't worked for you:

All of the above has not worked.

WHAT WORKED!?: 2 O-RINGS ON THE FUEL PUMP OUTLET SNOUT.

Attached is a picture of how, not only my fuel pump's o-ring setup was, but how I have found them set up in virgin stock fuel pump assemblies . My problem was due to the oring having the ability to become crooked/slanted and allow fuel to pass by. After installing the second o-ring, the seals now sit flush, allowing proper compression 360° around. After this, my ECM was trying to remove a bunch of fuel at multiple load points due to being tuned with this issue present at the time and the fuel pump having 3 different duty cycles. If you have a surge issue that you can't figure out, try this. Even if your stock.

Edited May 21, 2023 by Dillon
Added information.

[xt2005bonbon]

I only see one on the pic. 

I am actually about to install an AEM 340 65mm pump tomorrow on a car that has had some weird lean conditions at mid load/high rpm (>4000rpm). So not necessarily stumbling but lean enough to generate knock. I recall last year when I inspected the oem fuel pump, that one of the orings was damaged. I did not replace it  as I did not have spares at the time.

Edited May 21, 2023 by xt2005bonbon

[Dillon]

The picture is to show how it was previously. I have since added a second o-ring. Sorry for the confusion.

[Dillon]

Make sure you don't have a post MAF, Pre-turbo air leak. I suggest replacing at least the damaged o-ring, if not both. Unless, you only have one at this time, then I would suggest adding a second. I used silicone lubricant during install. Making sure damage wasn't going to be caused during install.

[xt2005bonbon]

Yeah I have spent a lot of times troubleshooting vacuum and boost leaks, and I am pretty sure I have none now.

I bought several oem orings for the fuel pump housing, and the aem pump came with two aslo. I'll change everything single orings for sure.

Edited May 21, 2023 by xt2005bonbon

[Pleides]

22 hours ago, Dillon said:

Make sure you don't have a post MAF, Pre-turbo air leak. I suggest replacing at least the damaged o-ring, if not both. Unless, you only have one at this time, then I would suggest adding a second. I used silicone lubricant during install. Making sure damage wasn't going to be caused during install.

Sorry if I'm just missing something from your post, but is the second o-ring just installed stacked next to the other one where it's supposed to be?

[Dillon]

Yes. I'll look to see if I have a second o-ring and retake the picture to avoid confusion. Unless someone can photoshop a second oring stacked on top of the first.

[xt2005bonbon]

40 minutes ago, Pleides said:

Sorry if I'm just missing something from your post, but is the second o-ring just installed stacked next to the other one where it's supposed to be?

Yes. I believe that's what should be done. I just checked instructions from deatschwerks and they even tell you to do that with their pump. (see screenshot below from their instruction doc -- I attached it here too). So I am going to do that with the AEM pump today.

 

 

08-14_Impreza_WRX_DW65c-300c_Fuel_Pump_Installation_Guide.pdf

Edited May 22, 2023 by xt2005bonbon

[Dillon]

Perfect example! Too bad it took me over 5 years to learn this myself. I've dealt with a stumble for far too long. Alot of stock and replacement pump assemblies only come with one! So everyone can be effected by this.

[xt2005bonbon]

You're probably right. Interesting that AEM is also providing two orings in their kit, but I can't find any AEM instructions online.. Pump is a 50-1215 btw.

Edited May 22, 2023 by xt2005bonbon

[Pleides]

42 minutes ago, xt2005bonbon said:

You're probably right. Interesting that AEM is also providing two orings in their kit, but I can't find any AEM instructions online.. Pump is a 50-1215 btw.

 

53 minutes ago, Dillon said:

Perfect example! Too bad it took me over 5 years to learn this myself. I've dealt with a stumble for far too long. Alot of stock and replacement pump assemblies only come with one! So everyone can be effected by this.

I'm so slammed with work/school right now but my stutter has been an issue for the life of the car and the AEM pump was only installed to ensure proper fueling for a tuned car. Wondering if Surgeline skipped an o-ring on the AEM pump install. The stutter was there both before and after, but it's worth a check.

[Dillon]

Absolutely!

[xt2005bonbon]

Brief update: replaced my oem pump with an AEM 340 pump. Brand new orings throughout and double orings on the pump itself. The thing works great but did not fix my lean condition. After further digging, it was a really a bad tune on the MAF curve (i.e. waaaay too lean between 70-100 g/s). I refined my MAF curve and now she is happy: no knock, long term fuel trims within +/-2%. If she stays like that, I'll restore the couple of degrees of timing I removed to gain my powa back .

So yeah, looks like my OEM pump was juuuust fine.

edit: forgot to mention I have a Cobb CAI. Whoever tuned that thing did a poor job on the MAF curve, as some portions of it still resembled stock set up.

Edited May 24, 2023 by xt2005bonbon

[Dillon]

I'm soon going to get a retune also. I'm switching back to a paper panel filter. I think the K&N messed with the maf during tuning. I'm also currently researching the fuel pump controller and bypassing it. I know how I will do it, if I do it. But I'm looking for pro's and con's.

[Max Capacity]

On 5/24/2023 at 11:26 AM, Dillon said:

I'm soon going to get a retune also. I'm switching back to a paper panel filter. I think the K&N messed with the maf during tuning. I'm also currently researching the fuel pump controller and bypassing it. I know how I will do it, if I do it. But I'm looking for pro's and con's.

Did you over oil the K&N ? I ran oil coated filters in my wagon since it had 4000 or so miles on it back in Aug 2004, I lightly oil them, never had any issues. I also clean the MAF yearly, with MAF cleaner. 

[Dillon]

It's very possible that I over oiled it, but I can't be sure since it's been about 5 years since it got tuned. I'm just trying to remove all the variables so the car can get a proper data feedback during tuning. 

[GearJamr]

I've had the stumble since I got the car a few years ago.  I've done a few of the suggested things to no avail.  I've ordered a new turbo inlet, tb to ic connector, fuel pump (dw 65c) and a new MAF.  Only thing left after that will be a fpr, but hopefully one of these things along with an updated tune will get rid of it.  So annoying to be getting on the highway at light throttle and have the car pretty much bucking through that 2500-3500 rpm range.

[Dillon]

If you have a way, monitor your avcs advance. You might have a bad avcs ocv solenoid. I have one go bad and it had some pretty bad bucking issues. It never threw a code or CEL, but the computer would stop operating it anyways. Maybe it didn't like the resistance value it was seeing. Beats me, but replacing the ocv solenoid fixed that specific issue. Good luck on your trial and error. These subaru's are a love, hate relationship.

[GearJamr]

Bucking is an over-dramatization.  There is a serous hesitation/stumble though.  Every time I have seen my tuner, he always says he's amazed at how healthy my EJ is.  Aside from the stumble, everything else checks out.  Good fuel trims, no timing change from the ecu, strong vacuum.....only issue is the change from open to closed loop.

Hoping making sure there are no intake leaks and making sure there is enough fuel supply (should probably have the fuel filter changed while the pump basket is out too) will get rid of it.

[Pleides]

FWIW I've spent thousands of dollars in time and money trying to figure out my stutter and never have. I think it's just a fixture of my car. No matter who tunes it, it always comes back the second the car is driven off a dyno.

[Dillon]

That's what I fear the most. I would like to hold on to some hope lol. What about people with after market engine management? Could it be due to a flaw in the the stock computer, coding, hardware, chips, solder joints? I've even scoped the crank shaft and camshaft signals looking for interference or electromagnetic induction, thinking it could be due to poor engine harness engineering. I bought my 05 lgt bone stock, and I don't remember it acting like this stock. So I feel it's either something I did, something that is no longer working properly or even deterioration of electrical conductivity or connections. I will say that there is one thing that I have still not understood. If monitoring the avcs degrees, right after reseting the ECU (before it initializes/learns its "0"/home), the left(driver side) intake camshaft will read 7° off. This has led me down a rabbit hole. I even sat down and counted the cogs/teeth on my timing belt to insure I was installing it correctly. I hate how the left bank doesn't completely line up with the timing marks. There are company's that make offset/adjustable timing belt idler pully's to adjust for decked heads and head gasket thickness. But I have not purchased one to find out if it helps. I've also wonder if the UEL exhaust manifolds cause some sort of unpredicted scavenging effect at the infamous 2.5k rpm. There has to be an answer. Just because it's a "subaru thing", doesn't mean it can't be fixed.