gc8fxt

It might be interesting to get a data log showing that stumble, with these parameters:

 

RPM

MAF

Load(calculated)

Final fueling base

AFR (preferably wideband but the stock sensor is fine for cruise and better than nothing for WOT)

Total ignition timing

Fine learning knock correction

Feedback knock correction

Knock Sum

 

I have a little theory that low ignition timing, caused by knock correction, is a big factor in stumble. It has been for me.

Have you logged your actual boost level and boost target? Maybe you are noticeably overboosting in that rpm range, and as a result, the 'turbo dynamic' related variables kick in and try to converge your actual boost level to target, giving you a sawtooth like pattern, resulting in what you described?

Give me a few days to get these logs. Busy guy.

Much of the stumble seems to go away when the engine is fully warmed up but even then it doesn't seem to have the power like I feel it should.

My old gc8 with a 20k was rated the same HP as this BP5 with 20Y and although the BP5 is a heavier car, it's not that heavy. The gc8 was silly, though, let's be honest.

edit: I did have a 14 FXT and my BP5 does feel quite a bit faster than that so maybe I'm overreacting.

So... I'm not sure how to explain the stumble...

Let's say I'm merging onto the highway in 3rd, I floor it because I want moar powah baby. Then instead of feeling the engine power/boost, I get this stumble. It will stumble between 3k and 4k rpm and then stops stumbling as it accelerates.

Sometimes I wonder if it's a boost issue. However, I also wonder if it's fuel pump issue (sometimes when I put my key to ON and you expect the fuel to pressurize, I hear what can only be described as a small whale/dolphin making a low volume mating call off in the distance -- car starts and runs seemingly fine). edit: I should add that if it's cold and if I accelerate up a hill at very low RPM it will surge like no tomorrow.

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both: both

MODS

Intake: stock

Exhaust: stock

Fuel: 91 pump - no noticeable change on 94 pump

Turbo: stock - td04hla

Engine Management: stock -- own a tactrix v2

Tuner and revision of tune(if you don't mind): none

MAINTENANCE

Sensors changed: none

Plugs changed: 1 step colder iridium

Coil Packs changed: none

OTHER SYMPTOMS

Check Engine Light: nope

Etc: -

RESULTS

What has and hasn't worked for you: changed to colder plugs and may have reduced stumble slightly... however, still there

If something worked, how long has it been working for: -