Subaru WRX Forum banner
1 - 6 of 6 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter · #1 ·
Hey Everyone. Have been a long time lurker here, but now I need some help / advice. Have a 2020 WRX and I'm having a strange issue with it that I have been chasing. Looking for any and all opinions, and curious to hear if anyone else has experienced any similar issues.

I did the Cobb stage 1+ tune a few months back (with the intake). Car is otherwise stock. Ever since I flashed it, in 2nd and 3rd gear I get a "stutter" when under wide open throttle. It occurs at peak boost every time. It's 2-3 small stutters and the car then continues to pull as it should. You feel the stuttering, but it doesn't jolt the car and it doesn't feel or sound like an engine issue. I've had faulty spark plugs and things of that nature in the past. This doesn't feel as extreme, and it feels different. It also does NOT appear to be a boost leak. You actually hear the BPV blowing off for a split second with each stutter. I've been trying to get my shop & tuner to diagnose the issue, but they haven't been able to analyze my datalogs yet. They road tested it, and their educated guess was that the stock BPV might be simply faulty / not able to hold my peak boost levels. However this would be the first time they have ever seen an OEM BPV failure with a simple Cobb stage 1 tune. They did not think it felt tune related. It felt more mechanical.

If anyone is good with datalog analyzing, I'd love to get some feedback. I have very little experience with datalogs as of yet. I captured a very concise and isolated occurrence of the issue. 3rd gear, wide open throttle. Stuttering happened twice. If anyone has any thoughts please let me know!

 

·
Æternum
Joined
·
15,935 Posts
Hmm, so this is really interesting and it makes me think that the FA20 boost control logic may be somewhat different than the old EJ logic.

I can see the "stutter" in your calculated load corroborated with a slight drop in boost pressure. Interestingly the TD boost error remains negative which suggests that the boost pressure drop (which is responsible for the load reading) is intentional by the ECU. This is where the interesting bit sets in. Just before peak boost, the ECU yanks back the throttle position despite indicating that YOU are on the throttle pedal 100% (in yellow).

Font Pattern Parallel Screenshot Number


I'm guessing this is an ECU logic to prevent boost spikes. Try installing the LWG map and report back here.
 

·
Registered
Joined
·
4 Posts
Discussion Starter · #3 ·
@zax Wow.....thank you for taking a look at this. That's more information than I've been able to come up with in the past month. I really appreciate it. I'm going to give the LWG map a try and I'll report back.
 

·
Registered
Joined
·
4 Posts
Discussion Starter · #4 ·
@zax so I reflashed the 93 octane LWG tune. It dramatically reduced the stuttering. It is much better. However, I’m still noticing very subtle stutters under full load. Much less frequently. They are barely noticeable, but I’m still catching them.

my shop is recommending that I try flashing the 91 octane tune next and seeing if that completely mitigates the issue. Do you have any thoughts on that? I’m concerned that there may be long term negative side effects to running 91 instead of 93.
 

·
Æternum
Joined
·
15,935 Posts
my shop is recommending that I try flashing the 91 octane tune next and seeing if that completely mitigates the issue. Do you have any thoughts on that?
Without seeing a new log, it's hard to comment, but I don't think a 91 octane tune will address what you are seeing. This isn't a timing adjustment due to fuel octane -- the ECU was physically closing the throttle plate despite your input request of 100% throttle.

Another thing I was thinking is that it could be related to the traction control. How's the road surface? You could try to disable the TC and see if the feeling persists.

I’m concerned that there may be long term negative side effects to running 91 instead of 93.
To be clear - they are suggesting to run the 91 octane tune and not 91 octane fuel. There will be no ill effects to running a 91 octane calibration with 93 octane fuel. The 91 map simply softens the global timing and slightly reduces peak target boost. The timing adjustment is not large enough to spike your EGTs so there will be no issues.
 

·
Registered
Joined
·
4 Posts
Discussion Starter · #6 ·
@zax thanks again for the feedback. Regarding road surface - it’s driven on nothing but smooth and normal roads. I’d be surprised if that was causing it, but I’ll give it a try.

I reflashed to the 93 LWG tune and it helped, however I was still getting small stutters. Much less frequently.

I reflashed to the normal wastegate 91 octane tune and have been running it for a few days. It was pulling great, no stutters, up until tonight. The air was very cool and I had more people in the car than I normally do. I did a few 1-3 pulls and got the same stuttering again. I can still try the 91 LWG tune but I’m not sure that would help.

Question for you — if I just get a good pro tune from a reputable speed shop, do you think that would completely correct the problem?
 
1 - 6 of 6 Posts
Top