Subaru Legacy Forums

Subaru Legacy Forums (http://legacygt.com/forums/index.php)
-   Fourth Generation Legacy (2005 - 2009) (http://legacygt.com/forums/forumdisplay.php?f=10)
-   -   Strange new acceleration issue - input appreciated (http://legacygt.com/forums/showthread.php?t=200691)

.:Catalyst:. 01-29-2013 10:20 PM

Strange new acceleration issue - input appreciated
 
So I've held off from posting this as I really wanted to exhaust my local resources for resolving a new issue before posting.

I recently had some 90K maintenance items done and a new issue has arisen (perhaps coincidence but anything is possible). New plugs, LWCP, accessory belts, trans/diff service and oil change were completed. My clutch needs babying as it's been slipping a bit under WOT so I went a couple days before needing a quick WOT pull to pass someone.

Now consistently, when in 2nd or 3rd gear, at WOT only, my car feels like I hit the rev limiter at 5K RPM. Every time - without fail. 25%, 50% or 75% throttle it will accelerate as expected, and doesn't cut out all the way to redline. When I hit that wall, I can lift and get back on throttle and the car drives smooth. Car is Stage 2 and drives exactly as expected except this one situation.

I talked with my tuner for input, as well as my local Subaru mechanic. Tuner had me log and it looks like I'm lifting off when the cut occurs (although I'm not). No CELs or codes whatsoever. I talked with my mechanic and he thought for sure it was the fuel pump. I wasn't sold this was the case, but since I planned on getting one down the road, figured I'd go with his experience and pulled the trigger on a DW 65C. Installed and the symptoms are exactly the same prior to the new pump.

I am open to input. I've cleaned the MAF, reset the ECU, installed a new fuel pump, logged FPDC and IDC and no smoking gun yet. Only occurs under full load at WOT. At this point the mechanic says it's the tune (finger pointing in my opinion), especially since my tune's been flawless for over 4K miles.

I truly doubt a tune would do this in general - especially after so many non problematic miles (and my analytical side says if you just had work done, and a new problem arises - must be related). My mechanic has been working on Subarus for many years and is pretty sharp and quite capable, but I think the tuning aspect of things is beyond him, so an easy place to shift the focus.

One other issue I have had occur a few times that seems like it's plausible it could be related is that occasionally when I'd be rolling into a stop, and clutch engaged, my car would rev a couple thousand RPM on it's own with zero throttle input , (even before I was tuned to stage 1 let alone stage 2). I'm wondering if it's related and maybe something with a throttle sensor, the DBW system in general, or is my car just possessed by throttle gremlins?

Open to input, things to try, or discussions that might flush out what the hell has started to act up in a normally healthy car.

BarManBean 01-30-2013 06:54 AM

Paging Strizzy...I believe he dealt with a very similar issue.

I don't think it was mechanical / tune related (per se), but I believe the final solution was replacing the ECU. I think he tried just about every single other option to no avail. Hopefully he will chime in.

.:Catalyst:. 01-30-2013 07:40 AM

Thanks BMB - this one has me stumped.

BarManBean 01-30-2013 07:46 AM

Quote:

Originally Posted by TonyRas (Post 4269625)
You know your clutch needs babying because it's been slipping. Your clutch is done, replace it.

Yes, he knows that :rolleyes:

.:Catalyst:. 01-30-2013 08:01 AM

This issue isn't the clutch. I know what clutch slipping feels like. RPMs don't jump under WOT at 5K RPM. Feels like someone throws an anchor out the back. Right at that moment FPDC and IDC drop as if I let off the throttle. I can reproduce this with 100% consistency, WOT, accelerate to 5K RPM and boom it hits a wall.

Underdog 01-30-2013 08:16 AM

The FPDC and IDC drop off as you lift the throttle, or are falling prior to and when you lift the throttle? I'd also be interested to see what the throttle is doing (requested and actual), as well as boost pressure and WGDC.

Can you duplicate it in any other gear besides 2nd and 3rd?

iNVAR 01-30-2013 08:41 AM

Post the logs.

Make sure IAM, FBKC, FLKC, Knock Sum, Throttle Opening Angle, WGDC, MRP, FPDC, IDC, RPM, Gear are in there.

.:Catalyst:. 01-30-2013 09:50 AM

2 Attachment(s)
Quote:

Originally Posted by Underdog (Post 4269669)
The FPDC and IDC drop off as you lift the throttle, or are falling prior to and when you lift the throttle? I'd also be interested to see what the throttle is doing (requested and actual), as well as boost pressure and WGDC.

Can you duplicate it in any other gear besides 2nd and 3rd?

They drop even though I'm not lifting (still 100% requested throttle). Here's the logs I've taken in both 2nd and 3rd gear. The 3rd gear log the event occurs, I lifted post event, and then back to WOT and it occurs again.

iNVAR I can add some additional parameters you mentioned and log again after work.

BarManBean 01-30-2013 09:56 AM

Looks like everything shits the bed right there (5k rpm)--Boost error goes crazy, IDC drops way low, MAF voltage drops...

Weird.

.:Catalyst:. 01-30-2013 10:17 AM

Quote:

Originally Posted by Underdog (Post 4269669)
Can you duplicate it in any other gear besides 2nd and 3rd?

Doesn't occur in 1st gear and haven't attempted in 4th (yet).

Zero1 01-30-2013 10:22 AM

Any sensors unplugged or a post-MAF leak? I had a similar issue when my "Big Foot's Dick" AVO inlet pipe slipped off my turbo. Interested to see what this is...

I won't even touch my probs LOL. I need a new clutch BADLY and want a motor/turbo build so much...

Underdog 01-30-2013 10:22 AM

I think the telling thing here is that your MRP is going from full boost to vacuum almost instantly (on 3rd gear log).

.:Catalyst:. 01-30-2013 10:39 AM

Quote:

Originally Posted by Zero1 (Post 4269889)
Any sensors unplugged or a post-MAF leak? I had a similar issue when my "Big Foot's Dick" AVO inlet pipe slipped off my turbo. Interested to see what this is...

I won't even touch my probs LOL. I need a new clutch BADLY and want a motor/turbo build so much...

No known leaks post-MAF. Love your analogy of the AVO inlet. IAM stays at 1, and fuel trims are within normal spec according to LVs.

.:Catalyst:. 01-30-2013 10:41 AM

Quote:

Originally Posted by Underdog (Post 4269890)
I think the telling thing here is that your MRP is going from full boost to vacuum almost instantly (on 3rd gear log).

That would coincide with the feeling of hitting a wall, but what is it telling us? That's the question I keep asking myself.

Zero1 01-30-2013 10:48 AM

Fuel cut is a mother @#$&(*. It is like being slapped in the face LOL


All times are GMT -6. The time now is 05:58 PM.


LegacyGT.com