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).

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

 

@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.

 

@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.

 

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.

 

@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?

 

Just wanted to follow up on this thread in case anyone else experiences the same issue with a 2020. I ended up having my car dyno tuned today. The tune feels MUCH better than the Cobb stage 1 OTS map. Significant improvement and a pretty sizable power & torque increase.

However, the throttle cut is persisting, exactly as it was when it first started happening under the stage 1 OTS tune. I’m kind of stuck at this point, not sure what else to try. I’m going to talk to the tunerthat dyno tuned it today. I think this pretty much confirms that it’s ECU logic of some kind. I’m not sure it’s something that Can be fixed or corrected. Either that or there is a physical component of the engine that’s triggering the ECU to cut the throttle under full load when the boost spikes / peaks.

 

Just wanted to follow up on this thread in case anyone else experiences the same issue with a 2020. I ended up having my car dyno tuned today. The tune feels MUCH better than the Cobb stage 1 OTS map. Significant improvement and a pretty sizable power & torque increase.

However, the throttle cut is persisting, exactly as it was when it first started happening under the stage 1 OTS tune. I’m kind of stuck at this point, not sure what else to try. I’m going to talk to the tunerthat dyno tuned it today. I think this pretty much confirms that it’s ECU logic of some kind. I’m not sure it’s something that Can be fixed or corrected. Either that or there is a physical component of the engine that’s triggering the ECU to cut the throttle under full load when the boost spikes / peaks.

Thanks for keeping infos coming, really interesting [emoji108] I wonder how the protune tuner just didnt do anything about your stutter, like; “Hey we got you way more power than before, but no worries the throttle is closing by itself at WOT… just sometimes just a second…” and you like you said, your back at Start [emoji107]


Sent from my iPhone using Tapatalk

 

Yeah, I'll update this thread if I manage to get any resolution. Oddly enough, the car did NOT stutter at all while being dyno tuned. The throttle cut / stutter issue started occurring about halfway through my drive home from the dyno appointment. And now it's doing it in every gear when applying full throttle.

Here are some isolated data logs from today....2nd and 3rd gear, full throttle is where the stuttering occurred:

Eckert WRX 1

Eckert WRX 1 Time (sec),AC Compressor Sw (on/off),AF Correction 1 (%),AF Learning 1 (%),AF Sens 1 Ratio (AFR),Accel Position (%),Baro Pressure (psi),Boost Extended (psi),CL Fuel Target (AFR),Calculated Load (g/rev),Comm Fuel Final (AFR),Coolant Temp (F),Dyn Adv Mult (DAM),Feedback Knock (°),Fine...

docs.google.com

Eckert WRX 2

Eckert WRX 2 Time (sec),AC Compressor Sw (on/off),AF Correction 1 (%),AF Learning 1 (%),AF Sens 1 Ratio (AFR),Accel Position (%),Baro Pressure (psi),Boost Extended (psi),CL Fuel Target (AFR),Calculated Load (g/rev),Comm Fuel Final (AFR),Coolant Temp (F),Dyn Adv Mult (DAM),Feedback Knock (°),Fine...

docs.google.com

 

I think I finally got a resolution. It was very simply overboost, like we suspected from the beginning. The tuner reviewed the logs again from after the dyno tune. Sure enough the car was overboosting by about 1psi, which is enough to cause the throttle cut / stuttering I had. The interesting part - they tuned it at 19psi on the dyno with no issues at all. I watched it with my own eyes. However, on the street the car produced a higher calculated load, causing it to overboost by 1psi. And it didn’t happen until about an hour of driving after the tune.

My tuner said that this is a common issue they noticed with 20 and 21 WRXs. They are extremely sensitive to overboost, and they typically road test after a tune to mitigate the problem. But with my car it didn’t happen on the road test. The older WRXs don’t have the ECU logic that physically closes the throttle plate when overboost occurs.

Ultimately they made some minor adjustments to my tune, and throttle cut stutter is gone. It’s pulling great. So if anyone with a newer WRX experiences this - here’s your solution.