Howeler

Great thread.

My 09XT has some hesitation like this, but mine seems to happen from about 1,500 rpms from a stop. Does seem like it's running too lean.

What's interesting is that it does not happen at all when driving in "sport" mode.

__________________
2009 Pearl White Forester XT Limited 4EAT Woot!

kurtaforesterguy

My '09 XT, in sport mode, is a little more responsive. It also keeps the transmission busy.

One aspect of the '09 XT is that "stomping" its accelerator makes the vehicle hesitate for 1 - 2 seconds, while a smooth motion of the accelerator lets the vehicle accelerate immediately.

Perhaps that characteristic comes from slow sampling of the accelerator position (everything's digital these days), or an emissions system delay wrt abrupt throttle changes?

My former Malibu Maxx, one of GM's first wireless throttle vehicles, had similar characteristics.
Its engine was a revamped turbo-less pushrod V6 that worked surprisingly well given its 1980's design roots.

BTW, The '09 "X" Forester actually has a more aggressive throttle attack than the XT does, which made the X annoying at stoplights. Ironic, given the X has minimal passing power compared to the XT.

stan_t

I've also thought that it could be drivetrain related, like the center diff not transferring power smoothly? But I don't know enough about that stuff.

Stan

__________________
"If you can use a hammer and sandpaper, you can do this swap, imho." -- jamesohoh7

Stein

My 07 xt pulses something like 1/2 second accelerating 1/2 second coasting, repeat repeat repeat. Just tonight I installed turboxs catless exhaust from turbo connecting to stock axleback. The pulsing is unacceptable almost. I looked over and it looked like my wife was jamming to some good hip hop music or something. Her head was bucking with the car. I could see some sort of snowballing/lagging compensation with fuel, boost, etc. I am definitely seeking an answer, just like the rest of you on this. I like the style, overall power, price of this vehicle, but driveability is poor, even when she was bone stock.

__________________
Strong, Cheap, Light...Choose 2

stan_t

Yep, you got it too. I drove another member's stage 2 '05 a while back and felt like his car did not do this.

Stan

__________________
"If you can use a hammer and sandpaper, you can do this swap, imho." -- jamesohoh7

Arthrogrian19

Sounds like wastegate flutter or compressor surge. Does your car sound like a sewing machine at medium throttle?

__________________
'08 FSXT, GRP, 4EAT

TSi+WRX

This makes me wonder - Stein, have you reflashed to "Stage II," yet?

If not, could his specific *CURRENT* exacerbation of this issue be specifically related to boost-control problems, given that he's gone full-catless turboback, but is on either a stock or "Stage I" engine mapping?

__________________
Me: '05 Legacy 2.5GT
Wifey: '09 Forester XT

stan_t

Hesitation has been there on all tunes I've been on at all stages, it just got worse as the car started making more power. I drove another member's '08 and I feel it on his car too, it just isn't as pronounced because his car is stock.

The Stage 2 '05 I drove that didn't do this had an aftermarket header-uppipe, not sure if that matters.

Stan

__________________
"If you can use a hammer and sandpaper, you can do this swap, imho." -- jamesohoh7

TSi+WRX

^ Do you know what ROM images your base-maps were based off of?

Regarding Stein's observations, I'm simply wondering if, in his specific case - that of observed worsening of this issue after turbo-back installation - may be, again specifically, associated with incomplete boost-control issues, stemming from running a basemap which is not suited to the new breathing characteristics of the vehicle.

Additionally, I also wonder if there's something to do with his revised post-turbo cat. setup - or the lack thereof.

LittleBlueGT, in the referenced thread on LGT.com, was able to significantly decrease his vehicle's observed hesitation/pulsing/"stutter/studder" by altering the front O2's behavior (or, rather, how the ECU is interpreting the O2's output) - but is the change that Stein effected in his post-turbo cats (and thus O2 sensor's "input") effectively causing a "cycle" where the ECU is now chasing something else which it cannot attain, much in the same way as LittleBlueGT's front O2 rescaling helped his ECU to suppress its own behavior in trying to chase that ideal value.

FWIW, I think that LittleBlueGT's attempt to address this problem (as it manifests on his vehicle) as well as Subaru's official response for the BL/BP platform - in implementing the 521N and 522N ROMs for vehicles on which owners complain of the issue - and the fact that this felt hesitation/pulsing/"stutter/studder" improves upon a basic ECU reset (which, itself, logically supports why LittleBlueGT's diagnosis and attempted fix is going the right route, as it's the ECU's "learned" behavior, in effectively chasing/responding to the O2 sensor's output, that caused much of his problems), if only temporarily, all points to a definitive ECU component to the equation.

Yet, the fact that hardware changes can also seem to exacerbate the issue certainly would seem to suggest that the ECU is not, alone, the cause, that there must be something more.

__________________
Me: '05 Legacy 2.5GT
Wifey: '09 Forester XT

stan_t

Not sure. I ran it stock, then Cobb Stage 1 (V2, AP-003), Cobb Stage 2, Cobb OTS VF43 map, then custom-tuned.

Stan

__________________
"If you can use a hammer and sandpaper, you can do this swap, imho." -- jamesohoh7

Stein

Late last night when I made the initial catless test drive I was still on stage 1 and it surged BAD. This morning I had more time, and reflashed to stage 2, but still pulses like normal. This is a strange event, like I've never had before and can't stress enough, how undesirable it is. It's not like it's gonna blow up, just like there is a little person magically closing the throttle a 1/3 of the way every half second. Makes you wonder if the DBW motor or something is bad, stripped, or otherwise.

The forester does not sound like a sewing machine. Just like the throttle is being closed on me a little bit in an even cyclical manner.

__________________
Strong, Cheap, Light...Choose 2

TSi+WRX

^ Well, there goes my theory on your specific vehicle/instance.

Now what I don't get is that if it's an ECU-related issue, your reflash should have at least temporarily "cured" things - given that the reflash is, itself, effectively a ECU reset. I don't get it.

OK, so I'm going to throw this one out there, just to be complete. Did you check all pre-turbo connections after the install? just in case something got snagged or displaced? or even "blown off" (i.e. one of those infamous "T" vac-lines)?

Certainly, a pre-turbo boost/vac-leak could lead to the tremendous driveability issues that you're describing.

I truly do feel bad for you, that your car seems to be suffering from one of the worse cases of this that I've ever heard of.

---


^ That's me, too. I'm also unsure of what I've got.

What gets me is that I can almost *swear* that, when my car was still stock, with what I'm certain was the 510N ROM (since my car was an early '04 production) - as well as with my rather early-on ECUTeK tune (fall of 2005, which pre-dates Subaru's introduction of the 521N as well as 522N ROM images), I did *not* see this problem.

Yet, my current tune, which was performed in the fall of 2006 - I do see just a little of this problem, in a very, very specific spot of my powerband.

What kills me is that I've got ECUTeK on this car - something that I elected to do BECAUSE of the ECU-"lockdown" that it imposed. It prevents me from messing with the car and blowing it up.

I therefore have never been able to read the ROM image.

__________________
Me: '05 Legacy 2.5GT
Wifey: '09 Forester XT

Stein

I did a passive scan today of all the fittings. I didn't actively touch and examine every vacuum line, but things do look good. I will check everything out. Also I could do a quick datalog and see if there are any obvious boost or timing "red flags". Hard thing is that it's not consistent. Seems like whenever you try to make it surge, it won't, it'll be just smooth, typical luck...
I'm leaving tomorrow AM for a week long work trip, I hope this thread doesn't die! haha

__________________
Strong, Cheap, Light...Choose 2

kurtaforesterguy

In various web archives I've read turbo surge is a common problem with many recent Subarus. The STI seems to have more than most.

Just guessing but this might involve intermittent airflow resonances occuring within intake _and_ exhaust system.
Without lining the airflow paths with pressure sensors, or having a _very_ accurate computer simulation, that could be very difficult to track down.

If there is pulsation occurring in my '09 XT' , I've yet to notice it.