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Old 07-18-2019, 12:37 AM   #1
codydr89
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Default 05 Outback xt. Jerking/bucking under boost

Hey everyone. Have an issue with my 05 obxt that I canít quite figure out. I work on all my own stuff, but this is my first turbocharged vehicle. Everything else Iíve had have been mostly pushrod NA V8s. Lol.

Under acceleration, doesnít matter if itís rapid or gradual, once the rpms reach about 2500 the car starts to buck and jerk pretty violently. If I keep accelerating through the powerband, it seems to smooth out after 3800-4000. Doesnít happen in 1st gear, but itís felt through the rest. Most noticeable in 3rd gear.

Some hopefully useful info:
Manual transmission

Had turbo, spark plugs, timing belt, pcv, and other related items replaced almost 10k miles ago(before I purchased the car)

Car is 100% stock

Only fill with 93oct fuel

I keep a religious eye on oil level

No CEL or even pending or stored codes

Doesnít really seem to lack power, just the initial building of boost is harsh.

The problem is more noticeable on hot/humid days.

It seems to cruise at 70mph just fine. Doesnít hesitate if I accelerate at that speed

Iíve cleaned the MAF, and visually checked for any loose or damaged intake tubing or vacuum hoses. All looks ok

Iím sure most you guys know these engines better than me. Lol

My initial thought is maybe a sticking or bad boost pressure valve/wastegate.

This a common issue with these engines? Any insight on what else to check?

Any advice is appreciated. Thanks
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Old 07-18-2019, 09:48 PM   #2
codydr89
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Has no one experienced this? Or even no insight on what it could be?
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Old 07-23-2019, 03:50 PM   #3
oaklandish_WRX
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MAF sensors wear out...as do boost solenoids and front O2 sensors.

Cleaning up electrical grounds under the hood never hurts. Boost leak test could be informative.

Check these out:
https://forums.nasioc.com/forums/sho....php?t=2740715

https://forums.nasioc.com/forums/sho....php?t=2639657

https://forums.nasioc.com/forums/sho...d.php?t=533787
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Old 07-23-2019, 10:03 PM   #4
GJCS22
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Have a Nice Day?

Any mods to the car? Any gauges you can monitor while it acts up or scan tool?

From what little I know and what you wrote, I suggest you take a look at your spark plugs. Even if they were actually replaced before you bought the car, you don't know what spark plugs its running and just looking at their condition could clue you in as to whats happening. Sounds like you either have a spark issue or running lean for some reason.
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Old 07-26-2019, 01:58 PM   #5
codydr89
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Quote:
Originally Posted by oaklandish_WRX View Post
MAF sensors wear out...as do boost solenoids and front O2 sensors.

Cleaning up electrical grounds under the hood never hurts. Boost leak test could be informative.

Check these out:
https://forums.nasioc.com/forums/sho....php?t=2740715

https://forums.nasioc.com/forums/sho....php?t=2639657

https://forums.nasioc.com/forums/sho...d.php?t=533787
Thanks for the links. Will read through them and see if I can resolve this
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Old 07-26-2019, 02:05 PM   #6
codydr89
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Quote:
Originally Posted by GJCS22 View Post
Any mods to the car? Any gauges you can monitor while it acts up or scan tool?

From what little I know and what you wrote, I suggest you take a look at your spark plugs. Even if they were actually replaced before you bought the car, you don't know what spark plugs its running and just looking at their condition could clue you in as to whats happening. Sounds like you either have a spark issue or running lean for some reason.
No mods whatsoever. All stock. And I donít have any gauges or data to look at. Just have a simple basic code reader

But I will have to check my plugs. So I can at least check that off the list.
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Old 07-26-2019, 07:16 PM   #7
GJCS22
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Quote:
Originally Posted by codydr89 View Post
No mods whatsoever. All stock. And I donít have any gauges or data to look at. Just have a simple basic code reader

But I will have to check my plugs. So I can at least check that off the list.
Please let us know how that goes
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Old 08-11-2019, 12:51 PM   #8
codydr89
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Well I changed the spark plugs and absolutely no difference. Put the old ones back in and kept driving for a week. Then the car is starting to act up REAL bad. I avoid boost otherwise it gets violent.

So I put the new plugs in again to see if anything would change. Nothing changed.
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Old 08-11-2019, 01:50 PM   #9
GJCS22
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How is it acting up? How do you duplicate it? Is it the same as before just worse?
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Old 08-11-2019, 04:04 PM   #10
Valarius Starchaser
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I would do a boost leak and smoke test sounds like your losing air under boost or gaining air post Maf and the fuel trims make it work but when you get under load it surges
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Old 08-12-2019, 11:22 PM   #11
codydr89
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Quote:
Originally Posted by GJCS22 View Post
How is it acting up? How do you duplicate it? Is it the same as before just worse?
Yes. Exact same, but much worse. I guess the best way to describe it is, for example, someone driving a manual transmission and taking off from a stop, and letting the clutch out without giving it much time to match the engine speed.

Itís very similar to that type of jerking/bucking sensation.

But I can duplicate it anytime the engine spins up enough to start building boost. Typically around the 2500 mark.

Doesnít matter if Iím at 1/4 throttle or 3/4 throttle. But the harder Iím on the gas, the more violent the bucking is.

So when it happens, I can either just let off the gas until it stops the bucking, and then continue on, or just keep accelerating through it, and itíll stop in the higher rpm range.

Every time this happens, the RPMs fluctuate rapidly too
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Old 08-12-2019, 11:25 PM   #12
codydr89
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Quote:
Originally Posted by Valarius Starchaser View Post
I would do a boost leak and smoke test sounds like your losing air under boost or gaining air post Maf and the fuel trims make it work but when you get under load it surges
Wouldnít that at least give me some lean codes to go off of? Iíve checked to see if I even had any pending codes, and I have nothing even pending
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Old 08-13-2019, 12:00 AM   #13
nfm
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- get a mechanical boost guage, see if boost oscillates, if so, your wastegate arm might have too much preload, or the BCS vacuum lines have kink/hole causing oscillations
- check for preturbo vacuum leaks, check for pre o2 exh manifold leaks
- get an o2 wideband sensor, see if there are erratic A/F's readings
- get a tactrix cable, start logging

right now you're pissing in the dark, you don't have enough concrete data,
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Old 08-13-2019, 11:51 AM   #14
Valarius Starchaser
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Quote:
Originally Posted by nfm View Post
- get a mechanical boost guage, see if boost oscillates, if so, your wastegate arm might have too much preload, or the BCS vacuum lines have kink/hole causing oscillations
- check for preturbo vacuum leaks, check for pre o2 exh manifold leaks
- get an o2 wideband sensor, see if there are erratic A/F's readings
- get a tactrix cable, start logging

right now you're pissing in the dark, you don't have enough concrete data,


Agreed
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Old 09-04-2019, 07:55 PM   #15
codydr89
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Alright guys an update:

A buddy of mine had a spare set of known good ignition coils that I could try.

And it fixed!

Never would have guessed coils honestly.
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Old 02-07-2020, 07:00 PM   #16
Jaeslay36a
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Default Same Problem!

I know this reply is somewhat reviving this dead post, but I'm in some VERY similar situations. I have the EXACT same bucking and violent jerking going on with my 05.outback XT. The only CEL I got were for a failed MAF, bank too Lean and cylinders misfiring on 2 and 3. I had a valve cover gasket that blew, seemingly starting this whole thing. I fixed that(ended up having to take it to a garage cause I wasn't prepared to pull the motor out just to fix a gasket. This being my first Boxer motor I wasn't aware of what I was purchasing at the time. But that aside, before I had gotten the gasket fixed I had to drive it to the garage,and the gasket blow out was so bad it was basically ejecting oil from the "hole" (for lack of a better word) at a rate of 3 quarts of oil in a 2 and a half mile drive to the garage. Well, all that oil spraying onto a hot motor caused QUITE a bit of smoke.. Thats when it started.. The check engine light came on.. I had the gasket fixed. I told the mechanic I only wanted the gasket replaced. So when I got the car back I drove it and noticed the jerking and bucking at low 2's (RPM's) and it wasn't that bad at first. But my busy life and the option of another decent vehicle and a Motorcycle that i used to get around with put the Subie on the back burner. Months later I focused on the Outback. Keep in mind every now and then I would drive it a mile or two down the road. So when i turned my attention to the issue again it had gotten MUCH worse.. I checked for DTC's.. Got back. Bank too lean, failed MAF, and cylinders misfiring on 2 and 3..i pulled out the MAF and the intake side was completely covered in a hardened black soot, from all that oil back when gasket went.. I cleaned it with crc MAF cleaner. And had to actually use a qtip to manually and yes VERY carefully clean the seemingly trashed MAF. When I returned it and drove,the difference was noticeable. It had more bottom end acceleration and it idled much more stable, no more stalling, overall better response, but the jerking and bucking were still there, and boost was basically so low it wasn't worth mentioning. I've been under the hood with a few friends that are hobby mechanics (subaru, VW, Honda owners) whom all have done several Project on their own successfully. There are NUMEROUS problems with this XT. Small things yes, but essential fixes.. So many hoses are dry rotted a where the clamps meet rubber causing small leaks of many dif fluids.. But from all this research I've done I just have a feeling this turbo issue is more along something that this guy was having issues with(person who made this post) my real question is, since I'm getting a misfire on two cylinders the obvious thing to start with would be replacing coil pack and plugs, yes? Well I've been told I might as well replace all four of them, is this true? This subie has 194,000 on it and had 187k when I bought it. I'm just wondering is it worth the trouble and time and money it's possibly gonna take or should I just move on? I really like this car and the potential in it is amazing.. But I'm just thinking Its so far into its life should I try and find another one? These cars are near impossible to find I have come to realize.. If anybody has any advice for me it be greatly appreciated
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