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Strange new acceleration issue - input appreciated


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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.

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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.

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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.
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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.

romraiderlog_Troubleshooting_06LGT5MT_3rdGear_20130123_125720-1.csv

romraiderlog_Troubleshooting_06LGT5MT_2ndGear_20130123_125430-2.csv

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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...

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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.
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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.
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Well to go full vac in your IM it would require either the throttle plate to be closed, all boost pressure to be vented, or all exhaust gasses to be bypassing the turbo.

The throttle plate closing was something I wondered (hence my questions related to DBW system/sensors in OP). Perhaps a throttle body replacement is worth pursuing (this would also replace the TPS on that side).

 

wtf....

 

Your throttle opening remains open at 100% yet your your MRP goes into vacuum. That can't be right...

 

Bad BPV/BOV opening up under heavy boost and high airflow?

It is a Forge BPV, running yellow spring. I also ensure it's clean and lubed every few months. I still have my OEM as well and that would be easy to put back in place for troubleshooting purposes.
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wtf....

 

Your throttle opening remains open at 100% yet your your MRP goes into vacuum. That can't be right...

 

Bad BPV/BOV opening up under heavy boost and high airflow?

 

Well, the reported throttle position stays at 100%. Could be faulty readback, however unlikely.

 

Even if the BPV/BOV was going wide open it shouldn't be pulling full vacuum against an open throttle/spooled up turbo. At least I wouldn't think so. Furthermore, the BPV is opened by manifold vacuum. If it was sticking open after the last time it was actuated, he wouldn't be able to build boost.

 

*edit* Just saw your note about changing out the throttle body. I would say it's at least worth keeping on the list for now.

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Seems strange that everything is a-ok, then the car gets a 90k and the problem starts immediately after.

 

Is it even possible that this is plug or coil pack related without having cyl misfire codes?

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Very strange indeed.

 

Everything has been perfect since we finalized the tune months ago and we have seen plenty of weather change as well.

 

The fact the fpdc and idc *as well as mrp and everything else* drop indicate a lift of the throttle other than the throttle plate angle itself.

 

Whats strange is the consistancy of it acting up at the same rpm/similar load values. I wish i was closer to do some in car testing.

 

Dave

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