kaelanfrost

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.

 

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

 

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My problem is actually fixed!! I've been having too much fun to write a response on this thread.

It turned out to be a faulty fuel pump, as it wasn't building enough fuel preassure for high load situations, and thus fuel cut. I'm not sure why it died, but it did have gas sit in the tank for about a year so maybe that had a role in the failure. It is a super easy fix, just make sure you get the right pump as I heard some replacement ones stick too far down into the tank and hit the bottom! So bottom line, if your car is stumbling HARD when in high load situations, it's either boost or fuel cut from what I've heard, and if you log your boost with ecuExplorer and a vag-com KKL OBD2-USB cable, you can find out if you are lacking boost and if not, give the fuel system a go!

This is a link to the pump I used as well as a step-by-step procedure. Even though I didnt need a high-flow pump, I couldn't find many stock ones if any. Hope it's not a crime to link another thread!

http://www.uklegacy.com/forums/index.php?/topic/106366-fit-hrc-255-lph-340-fuel-pump-bh5-be5-simple-job/

You problably did already post it, I just was done reading through 18 pages of old threads.. but good suggestion!

Turns out it was a fuel pump, I read a guide on uklegacy;

http://www.uklegacy.com/forums/index.php?/topic/106366-fit-hrc-255-lph-340-fuel-pump-bh5-be5-simple-job/

This explains in detail what pump you need, and how to install. So if your car is experiencing what feels like boost cut, or fuel cut (like hitting a wall when you put your foot down) then try a logging software like ecuexplorer (the only one that worked for my JDM 2000 Legacy B4) and get a VAG-com KKL cable to connect the car to your laptop. See if your getting a large drop in boost when it cuts out and if so, then its a boost problem. If not, consider changing your fuel pump or looking into other fuel related issues (Regulator, injectors).

Thanks for all the suggestions! -Kaelan

have you looked at your injectors? something happening to them as the engine warms up?

I have deduced that it is a fuel problem, and probably a failing fuel pump as the problem is never consistent, and it doesn't seem to give the engine enough gas at high load high rpms. If it ends up not being the pump, then regulator and injectors will be next.

https://drive.google.com/file/d/1JsVJf7PuN-e2Fa7zvzGikcNXumam0Kmx/view?usp=sharing

https://drive.google.com/file/d/1xxK49MrC1R4_wUeYNu23jhoP5Tcx-EMw/view?usp=sharing

https://drive.google.com/file/d/11JwK2Zxb_mUMOjV7l_-aD7CchVR-yiJI/view?usp=sharing

these are some data logs. Cutout only occured in the 3/4 throttle pull as it seems to happen with a more heavy foot, and it happened right before I let off (around the max rpm I acheived)

Edit- It didnt name the first log for whatever reason but that one was just primary boost pulls almost to WOT. Also should my Cam position sensor signal be doing that??

I'll chime in:

 

2006 Spec B

 

TYPE OF STUTTER/STUMBLE

 

Increasing throttle/Medium input

 

MODS

 

Intake: Stock

Exhaust: full turbo back, GS UP and crosspipe, ported stock header

VF52

New stock injectors and newer sidefeed rails

GS TMIC

TGV deletes

Perrin inlet

Two extra OEM fuel dampers + Radium Eng damper on fuel intake side

Radium Eng FPR

Engine Management: stock ECU

Tuner and revision of tune: Mike at Tuning Alliance + DBW tables revised by me based on Throttlehappy tips from Nasioc

 

 

MAINTENANCE

 

Sensors changed: Bosch O2 sensor few years back

Plugs changed: NGK few years back

Coil packs: OEM few years back

Air Filter: Changed every 5k to newer OEM model (12A)

OCV valves: OEM few years back

 

RESULTS

 

Biggest change had been adding extra OEM fuel dampers to the fuel line, and redone DBW tables to open the throttle plate more at lower RPMs. Now there is zero stutter!

As I understand, a fuel damper stops the fuel preassure from occilating too much when the injectors open and releive some of that preassure? So adding extra ones makes it even smoother?

Just chiming in here: I had been complaining about a stutter to my mechanic for a year or more until I, per the recommendation of members here, replaced both AVCS oil control valves. Stutter went away completely for about two days then came back as they got clogged up again. My prior commute to work was three miles and the car didn’t even fully get up to temperature during the drive, which I think made it worse. I’ve since run some Liqui Moly engine flush through the oil and the OCVs are clean again, thus the car drives great until whatever sludge in the oil gunks them up again. I’d notice a decent improvement every time I had an oil change, too, which has led me to change the oil every 1-2K.

 

May not be the source of your problems, but the car will behave so erratically (mine had no CELs either) and it can be hard to trace when these things fail.

Can't hurt to try! I'll run some sauce through my oil and see if it can clear anything up!

Have you done a boost/vacuum leak test smoke test ?

 

I pull the hose off the air filter box, plug it with a pint size paint can, pull the small hose off the blow off valve, give that hose a short blast of air from a compressor, put your thumb over the hose, listen for leaks.

This is clever and I will definitely give it a go, but I am 99.9% certain it is not a vacuum leak. My boost logs show 12 on primary and about the same on secondary until it cuts out :/

Another thing to note is the cut-out is not at all consistent. Sometimes it at half throttle and 4000rpm, and sometimes it pulls full throttle to 5500 then cuts. All very weird. This makes me think electrical, or a half-broke sensor that freaks out when it malfunctions. Another note is that my gas cap seems to be holding a vacuum in the tank, since when I take it off after driving it gives a ssssss but I'm quite certain it isn't positive preassure as the cap isnt being pushed off when I unscrew it.

Fallowup:

The car actually stalled for the first time today:(

At first the stumble only seemed to happen once the car was warmed up and I've been driving for a while, but the stall happened in the morning when the temp was still climbing. It also seemed to only stumble around the 4000-anything more than that range, but more rarely it stumbles when going from a stop at a traffic light or such. I have to push the clutch back in and give it gas so it free revs up before i can actually get it to move (when it stumbles it feels like the throttle pedal has absolutely no input whatsoever)

It is super frustrating to deal with, mostly because I just bought this subie and I want to drive it!!! I still do not understand how no such issues occured on the test drive (it was thorough, through all the gears and up to about 5000, but it was hard to give it all the beans as it was right in the city!)

As I do not think ignition is my issue, with newish DP Boosted NP-421 ignition coilpacks (I couldn't find these on their website so a little confused), and brand new properly gapped spark plugs.

It feels as if the engine decides that I let my foot off the gas, but it is NOT. I have logged some data, which I can provide a link. If anyone can tell me if something looks off, that would be fantastic.

I already posted this problem on another thread on this website, didn't realize there was a dedicated thread... sorry. Anyways I bought this car not long ago and somehow this problem never occured on the test drive.

TYPE OF STUTTER/STUMBLE

Increasing throttle/Medium to heavy input

MODS

Intake: Stock

Exhaust: Blitz NUR spec S axleback

Fuel:Stock

Engine Management: ECU was sent to MINES for a reflash and some other things (Really hoping it isn't an ECU fault $$$!)

Tuner and revision of tune:

MAINTENANCE

Sensors changed: O2 sensor with Bosch LS02 (USDM equivalent that was actually avaliable)

Plugs changed: NGK PFR6B equivalent gapped to 0.65mm

Coil packs: Previous owner changed them for aftermarket ones, they looked good and I'll have to pull one out to get the brand and see if they 100% fit on this car.

Air Filter: Changed and good.

OTHER SYMPTOMS

CEL: Yes, was given just code 23 for MAF with the black plug test, and given just code 32 (O2 sensor) when i attempted to reset the ECU by connecting green and black conenectors (I fallowed this procedure correctly)

Note: This car was sitting for about a year, and had a near full tank of gas. When I took it home, I barely was limping it up hills the stumble was so bad. It didn't matter how much throttle it was given, the engine still just gave up for a bit (never stalled when this happened, just stopped revving up and the revs fell slowly as I'm waiting with my foot on the gas pedal) it seemed to happen whenever it was given gas.

RESULTS

After changing the O2 sensor, my code went away, and the MAF sensor code was just because I pulled the plug out when the car was running to see if that would help (I heard this can eliminate the sensor as an issue on other cars, but the engine died immediately so i guess not on these older subies.

I drained the bad gas as I thought this was the issue, and after cycling a couple tanks with some octane booster and i also tried an injector cleaner, although the stumble was almost never present at low RPM/speed, whenever I gave it the beans, the car stumbled just as hard. I pulled the fuel filter to inspect it and it was disgusting. As I didn't have one on hand, I cycled some fresh fuel through the opposite direction of the filter and blew it through. I have a filter coming any day, and even though I doubt it will fix it, It was certainly time to change the filter.

I'm running out of ideas as I have no more hints to fallow since it still stumbles just the same after the O2 sensor change. I was successfully data logging when the car was stumbling, but although I tried to interpret it i realistically don't know what I'm looking at.

Another update;

After a few tanks of gas, it seems to run very well up until the secondary boost kicks in around 4000-4500 rpm. I'm not sure if it's actually a boost problem, or if it is just because I'm at near to, or at full throttle when I'm in this rev range.

This was all before I found a thread:

https://uk.subaruownersclub.com/forums/topic/2366-manually-reading-ecu-codes/

This explains how to "reset" the ECU, or in my case show me a code that just the diagnostic mode (also explained) didn't. This thread also explains how to read the morse-like code given by the CEL.

When just the black connectors were plugged together, I was given code 23 for MAF sensor

When I attempted the ECU reset function, instead of the confirmation that it was completed successfully, indicated by a consistent flash of the CEL, I was given code 32 which is faulty O2 sensor!

However, I'm also reading that the O2 sensor doesnt really impact the high rev-range. I also unplugged the front O2 sensor plug, and the exact same higher-revs hesitation occurs. So does this mean that the O2 sensor isnt the prob?

Bosch LS02 should sort you out if you're rev C.

will this fit on a Rev-B?

Sorry to revive an old thread.

Changed spark plugs, they are gapped correctly. The car runs smoother but still stumbles when on heavier throttle.

The old plugs had rust on the top, not on the electrode and I’m sure this wasn’t helping the performance but it still didn’t solve the problem. The coil packs looked to be in good shape, as they are brand new aftermarket ones.

I’m thinking the bad gas had some impact on the fuel system, so checking injectors now might be a good idea. I did use a fuel injector cleaner so I assumed that would hopefully be rid of any fuel problems.

Hello all,

I recently purchased the above-mentioned car, and it is having some issues.

When cold the car starts no prob, idles fine, and drives great too, pulling nicely without any stumbling. However, after the car is all warmed up, and has been driven for a good 10 minutes (give or take) when the throttle position is anything from 1/4-full, the car builds boost nicely and starts to pull hard on the first turbo, but consistently around 3000 RPM it stumbles HARD and it feels like the engine cuts timing or fuel or something to prevent damage to itself. It jerks on and off even if I keep my foot as still as humanly possible (not letting the car jerk my foot forward and back). This same issue occurs higher in the rev range too, i.e. if I slowly let the car pass 3000rpm on very light throttle to just about anything above it and gun it, then the same thing happens.

See, I would guess I have a boost leak or bad knock sensor or something along those lines given what I've explained so far, but the peculiar thing is that if the car is completely warmed up, then shut off for a few minutes (like when I'm filling up) then driven again, the car pulls hard under WOT without a single stumble all the way up the rev range (5000 is redline in my mind until I change the oil). I know for a fact it is making boost on the second turbo, and the car is already warmed up completely so I would guess any splits in boost lines or piping would leak boost if that is the problem. But after a good pull and a minute or two, the car stumbles just as it did before.

Some things to note;

-The car has a Mines ECU that has been sent to them and reflashed (has the Mines plaque on it so it is legit)

-"new" ignition coils and plugs (I say this because I am completely prepared to replace both

-the gas cap, when removed is under pressure and hisses as it's unscrewed (with a final puff when it's completely off)

-No CEL (this is subject of discussion as well b/c it is a JDM car, and the scanners I've tried don't speak SSM (a special Subaru ECU language) but this can be solved when I find the proper adapter.

-car has 80000 km, so hoses are unlikely to be leaky.

-The car was sitting for about a year before I bought it, and it had a full tank of gas the whole time, which I have to drive home on and this is when the stumbling started (somehow never happened during the test drive) but fresh 94 and injector cleaner made it much better, but far from fixed.

So my question is, did the bad gas really do this all to my engine? If so, why does it still run as I described?

I'm going to look for clogged breather lines for the fuel tank, and post an update.

-kaelan