2005 OB XT hestitates on accel. Best way to diag?

[Norskie]

As the title says ... my 2005 OB XT hesitates / stutters on moderate acceleration. Idles smooth, does ok on small throttle openings, pulls hard and smooth on WOT, but the mid-throttle stutter at about 2500-3500 rpm.

 

It has been doing this for 10 years / 130k miles. It's annoying, and I've finished other more pressing issues so now I get to tackle this one. No CEL or pending codes.

 

Any ideas for how to start diagnosing the problem?

[whitetiger]

Cobb AP stage 1 tune.

[MTBwrench]

Sounds like a fueling issue. The question is whether it's a fuel harmonic, or tune related. If you're still on the stock ECU map I'd say it's a safe bet that a quality aftermarket tune will work wonders. That is, assuming everything is mechanically in order.

[Norskie]

Sounds like a fueling issue. The question is whether it's a fuel harmonic, or tune related. If you're still on the stock ECU map I'd say it's a safe bet that a quality aftermarket tune will work wonders. That is, assuming everything is mechanically in order.

 

Exactly. I don't want to throw $650 at an old car and find out a tune didn't help. Then again, I suspect I can recoup most of the cost of the AP if it doesn't fix the problem ... but if it does, I can still recoup the AP cost when we junk the car.

[whitetiger]

this sounds like the classic stutter that all earth BL/BP turbo cars experienced. the tune is the solution. the AP is a good investment. you are guaranteed to sell it for close to original value. IF not, at half value when cobb comes out with a new one. So at most you are losing $325 to potentially fix this.

[Norskie]

Is the AP a "plug in, reprogram, unplug" deal?

 

This is the family beater and I don't really want to have the family deal with it.

[whitetiger]

yes, its main function is a ECU software upgrade delivery system. once you flash in the map, you dont have to leave it plugged in. you just keep it in your glove box or in storage till you needed it again.

[Norskie]

I don't suppose I can use one AP to program both the Outback and a BRZ, just by downloading different maps?

[whitetiger]

no. the AP gets married to the car you use it for.

[RoscoeOutback]

I have the same issue with my bone stock 2008 Outback 2.5xt with 5sp Auto. I wasted a lot of time chasing vacuum leaks, be they in a hose, a gasket, or a crack. Never really found a smoking gun. I suggest you start by disconnecting the front O2 sensor amd driving it a while. Doing so puts the ECU into open loop, which means it is running a canned program instead of using data from ten or so different sensors to control fuel/air/spark for your local condition. If the car runs better, then you have a pretty good sense that it is one or more of said sensors giving you trouble, rather than something like worn plugs, transmission problems, head gasket, Valve condition/setting, timing, or something else that the ECU is not designed to correct for. If it still runs poorly in open loop, look to one of those other fundemental conditions.

 

If it runs bettter in open loop, drive it that way for a couple weeks. Put at least a couple hundred miles on it, a tank of gass maybe. Still good? Plug the front O2 sensor back in and see if the hessitation returns. You may need a couple drive cycles for it to return.

 

If the hessitation returns, you have learned that the problem is either:

 

A. the O2 sensor itself is bad (not far fetched), or

B. one of the other sensors is bad or misadjusted, or

C. a vacumm leak is fooling one of the other sensors, or

D. a poor ground under the hood is making the ECU misread one of the sensors, or

E. There is an electrical issue at one or more sensors. A dirty contact or broken wire, or

F. A faulty ECU

 

Im sure the folks on this board can add to this list, or give you a better explaination, but thats my two cents. I listed the potential issues above A to F, in the order I feel is most common or probable, to leasr common and least likely.

 

Good luck. Let us kno how to its going.

[Norskie]

no. the AP gets married to the car you use it for.

 

Ahhhh ok - that explains the concept of "unmarried" AP's I see in the used market.

 

Is there a process to "un-marry" an AP when I'm done with it, so that I can resell it later?

[whitetiger]

when you un-marry it, you flash back to your OEM map, so the stutter comes back.

 

but if you are selling or getting rid of the car, yes, you just un-marry it from the car and sell it.

[RoscoeOutback]

Ahhhh....I see that I absolutely misunderstood the original post and that y'all are on to bigger and better things. Nevermind. Lol;)

[Norskie]

I suggest you start by disconnecting the front O2 sensor amd driving it a while.

 

That's a good idea! Thanks, I'll give it a try.

[mx5]

As the title says ... my 2005 OB XT hesitates / stutters on moderate acceleration. Idles smooth, does ok on small throttle openings, pulls hard and smooth on WOT, but the mid-throttle stutter at about 2500-3500 rpm.

 

It has been doing this for 10 years / 130k miles. It's annoying, and I've finished other more pressing issues so now I get to tackle this one. No CEL or pending codes.

 

Any ideas for how to start diagnosing the problem?

 

Ha! I also have 2005 OB XT at 130K miles with that exact same annoying problem. I also have a 2013 WRX (which is pretty much the same car, sans turbo, ECU and air pump and I guess one less cat?) and in comparison the difference is night and day - the WRX feels alive at moderate acceleration with zero hesitation. I really want my Outback to feel the same.

 

Here is what I have recently replaced on the OB XT while trying to tackle the issue and which did not NOT fix our problem:

 

- all vacuum/pcv/etc. hoses with new silicone ones and clamps everywhere (had some small vacuum leaks from the hardened rubber which were causing stalls when going to a stop and that got cured)

 

And and all these with brand new OEM ones:

 

- Both air tubes between the air filter box (OEM) and the turbo (because had small tears near the hose clamps)

 

- PCV valve

 

- Air filter every 2 years

 

- MAF sensor

 

- Throttle body

 

- Fuel pressure regulator (simpler one from a '04 STI - some claim it cures hesitation but it didn't do anything)

 

- Turbo (at 80K miles)

 

- Spark plugs

 

- O2 sensors every 2 years

 

- Alternator (the original one started making a noise because of bearings going bad)

 

- Power steering pump (the original one started leaking)

 

Also:

 

- Fluidampr crank pulley

 

- WRX flywheel with Sound Bend Stage 2 clutch

 

 

I also bought a VAG COM cable and BtSssm (which I am running full time on an android headunit) but I haven't noticed any issues so far (misfires always at 0). Attaching a screenshot of my learned values here.

 

Next mod will probably be a STI OEM fuel pump and filter, and a GFB recirc valve but I am starting more and more getting convinced the cause is just a shitty OEM ECU tune.

 

[M. Schneider]

Many thanks for the "Critical path-like diagnostic's" and the MY05 Subi OB XT ....

Our Subi Outback XT has exhibited this common "good to great" stumble/studder-ish condition much of its life. Thanks again for the diagnostics step. Before jumping head-on for a ECU full tune.

 

I have the same issue with my bone stock 2008 Outback 2.5xt with 5sp Auto. I wasted a lot of time chasing vacuum leaks, be they in a hose, a gasket, or a crack. Never really found a smoking gun. I suggest you start by disconnecting the front O2 sensor amd driving it a while. Doing so puts the ECU into open loop, which means it is running a canned program instead of using data from ten or so different sensors to control fuel/air/spark for your local condition. If the car runs better, then you have a pretty good sense that it is one or more of said sensors giving you trouble, rather than something like worn plugs, transmission problems, head gasket, Valve condition/setting, timing, or something else that the ECU is not designed to correct for. If it still runs poorly in open loop, look to one of those other fundemental conditions.

 

If it runs bettter in open loop, drive it that way for a couple weeks. Put at least a couple hundred miles on it, a tank of gass maybe. Still good? Plug the front O2 sensor back in and see if the hessitation returns. You may need a couple drive cycles for it to return.

 

If the hessitation returns, you have learned that the problem is either:

 

A. the O2 sensor itself is bad (not far fetched), or

B. one of the other sensors is bad or misadjusted, or

C. a vacumm leak is fooling one of the other sensors, or

D. a poor ground under the hood is making the ECU misread one of the sensors, or

E. There is an electrical issue at one or more sensors. A dirty contact or broken wire, or

F. A faulty ECU

 

Im sure the folks on this board can add to this list, or give you a better explaination, but thats my two cents. I listed the potential issues above A to F, in the order I feel is most common or probable, to leasr common and least likely.

 

Good luck. Let us kno how to its going.

[Norskie]

I've done the tune - Cobb AP stage 1 @ 91 octane. It helped; it wasn't night and day different, but I think the hesitation is gone, and what remains is driveline lash. I haven't driven it enough to really tell, and it's very subtle so hard to say definitively. At this point, I am satisfied. Thanks for your help!