Car is cutting out around 4000 rpm

Hey first post but long time lurker. Recently my car will pull absolutely fine but going WOT around 4k will cause it to suddenly cut out almost like a heavy knock. 100k on the car with an OTS 93 tune. Other than that it's completely stock. I have a data log I hope will help since I'm not totally sure what I'm looking at.

datalog4.csv

Can you do a datalog in 3rd gear WOT from 2500rpm to 6krpm. That would be more helpful. This log shows small throttle inputs and its hard to say what is being done by the driver and what is being done by the ecm.

 

Was there anything done before this happened? Have you noticed any other issues?

I have a log in second from close to a stop to when it starts cutting. I didn't want to try and push the car through and potentially damage anything. Only recent change was a DW300 installed when this issue started because I assumed it was a fueling issue.

datalog2.csv

I see the spot around 40 sec where you went WOT I don't see anything abnormal but your boost error is around 1-3 psi. Usually you want to start by checking for boost leaks, the throttle body coupler is a common culprit especially if it still has the gasket ends on the factory hose.

Also try cleaning your MAF and reloading your tune, did you recently get fuel at a different place or a different brand of fuel?

I recently got gas but it has been a consistent problem through 2 tanks but I have filled up from the same chain at stores within a couple miles of each other. I'll try stepping back to a 91 tune and seeing if that might be the problem. Something tells me I might have gotten some bad gas. MAF will get pulled and cleaned tomorrow. Thanks a ton so far, hopefully I'll have good news to report.

Had similar and it was due to overboost.

 

https://legacygt.com/forums/showthread.php/fuel-cut-5k-ish-rpm-overboosti-283344.html

So quick update while I’m on break at work. Reflashed the ECU this morning with the original 93 map and the stutter was less pronounced. I’m going to try the 91 map on the drive home and see what happens. I can try and get a couple good data logs comparing what the car is doing between 91, 93, and maybe even stock. No CEL or even a flashing CEL during the stumbling. MAF will be pulled and cleaned thoroughly again. Did a preliminary look at the vacuum lines I could see and everything seemed secure and still flexible. Could it be plugs? Still not hitting target boost of 17 psi and averaging around 15.6-16.4 peak. I looked at the intake and the charge pipe boots and saw no cracks and everything was butted up to the metal end fully.

Is it falling flat on it's face around 4k and WOT or is it stumbling or just not hitting target boost?

 

I'm thinking the classic rubber boots between the intake and intercooler might be leaking. At 100k they could be getting funky and cracked.

It’s basically a hard bucking and feels like the motor cuts out for half a second and continues. The tach will bounce but still climb. Problem is only an apparent at WOT or close to it. If I just push 10 pounds through it by laying off the pedal a bit then there’s no problem at all.

Sounds like an overboost condition to me. The ECM cuts boost like a hammer when it happens. I had it happen to mine and it was abrupt.

I would double check to see if all the hoses to and from the turbo are hooked up and not cracked. If you lose one of those it could easily cause an overboost issue... ask me how I know...

 

I would still look into the throttle body coupler because there's been a lot of them messed up around here and can create a boost issue under load. Check out the pic in this thread.

https://legacygt.com/forums/showthread.php/stewdoggs-2010-gt-269205p14.html

You just pull those end pieces off the coupler pipe.

Where are you located, and how long have you been running the tune? I also had the 93 OTS map and my car would seem to lose power in colder “boost” weather. I always just assumed it was to prevent over boosting, but it was consistent with changes in ambient temperature, and happened every winter.

Yeah I would agree. The first time I overboosted (to 27.4 PSI!) I though my engine had blown.

 

Also, once you overboost, you can have resultant boost leaks if you crack the charge pipe or blow off a hose. If your idle, cruising, and low boost AFR is normal, than this is unlikely.

So update, drove home with the 93 map. Not a single problem at all. Got home and had the car idling while I loaded it for a trip to the house I recently bought. Issue started again after leaving. I’m going to try and look through all the vac lines and especially any of the intake piping this weekend. Just taking it easy on the car from now until I can get it on ramps and look underneath. Could it be a turbo issue or a bpv issue as well? I’m seriously at a loss of what could be causing it. Today’s temps were 42 at 5:30 am and 65 at 3:00 pm. I’m in southeast PA.

I know your coming up short in boost, but your vacuum looks like it’s in good shape. If it were a leak and only occurred during boost but not in vacuum, it may be some component of the charge piping system. The stock bpv is prone to leaking above 12 psi.

 

Is this something happening consistently in one gear at on rpm, or all gears at that rpm. Any other symptoms you notice?

 

Have you done plugs recently? You mentioned bucking which makes me think misfire.

Haven’t done plugs, no flashing CEL for a misfire during the bucking. It’s usually at 4K rpm in any gear but it’s most apparent in third. I haven’t gotten a single code to pull yet despite it happening multiple times.

Yeah check the throttle body coupler

Pulled the coupler today. The little inner flap had torn and pushed out on the TB side. Reattached it with everything clamped tight and going to see what happens. If I need to replace the boot will the Cobb silicone one work?

Did you pull those inner flaps off of the throttle body coupler on both sides and then reattach the coupler to the car?

I cut away the damaged parts of the inner flap and then reattached it and made sure to really tighten it. Problem has noticeably improved from a harsh cut out to a minor stumble in boost now.

Any throttle body coupling for the 2015+ WRX will work, no need to spring for a name brand.

Not the best timing now that things are back together, but you can just remove those rubber gaskets entirely with no ill effects, things will seal up just fine. I forget if re-flashing a tune erases the learned parameters from the ECU, so it might be worth disconnecting the negative cable from the battery for a minute or two to reset those learned values. Assuming the throttle body coupler is the only mechanical issue (which it may or may not be), the ECU could still be trying to compensate for something that's no longer a problem.

I forget if re-flashing a tune erases the learned parameters from the ECU, so it might be worth disconnecting the negative cable from the battery for a minute or two to reset those learned values.

 

It does with open source tunes, not sure about Cobb/AP tunes.

 

Definitely reset it and let it relearn, but I'd remove those things completely first.

I'll be removing them tomorrow after work and resetting the ECU. It definitely seems like the inner flaps were causing some boost issues. Driving today the AP was reading 16.5 PSI peak which is only a half pound below target. Still some stumbling present. I'll see how it works tomorrow and if still no luck I'll have to order a new coupler. Any suggestions?. A quick search only showed cobb, perrin, and avo options. Nothing generic seemed to pop up.