VersaTune User Forum

Hello all, I am working on self tuning my 2007 speed 3 on 91 Octane and am running into what I believe to be fuel cut and could some help.

Relevant mods:
-Autotech HPFP
-CST4 turbo
-Mac 3 port EBCS
-JBR 3.5 inch intake, bosch 3 bar map
-CPE TMIC
-CPE Catted downpipe
-NGK LTR7IX-11 (one step colder) plugs gapped to .026
-uplugged EGR
-unplugged SWAS
-Built motor (forged pistons, rods, arp head and main studs, BSD, stock compression ratio and cams, kinda standard build)
-Damond Engine mounts
-Maybe less relevant: 2nd gen trans, spec "stage 3+" clutch, catch cans, external oil cooler

The journey so far:
-mafcal done, map scalars inputted
-started with 0 WGDC, stock load limits
-started working load limits and WGDC up slowly. Eventually got to a point where at WOT, WGDC would decrease after a certain RPM instead of stay constant as I set in my BCS DC Base Extended table (load targets were all set to 2.5 and i was only getting to ~1.8). Set BCS DC Adjustment - Decrease to 0 and it """fixed""" it, will need to go back later and figure that out later...
-I continued upping WGDC and requested load, did another mafcal at the higher load levels
-At some point (~20 psi of boost or so, ~1.9 load, something like that), the engine "hiccuped" at ~5k RPM. it only lasts a split second and sometimes doesnt show up in data as power comes right back but it is VIOLENT. Happens in multiple gears as well and goes away when i go back to 0 WGDC.
-I tried upping all the load limits to 3, upped boost limits to 30, tried turning TSC off, still does it...
-Decided to check on the hardware side: changed plugs, borescoped cylinders, changed oil, looked to see if anything was out of place... and while it looks like it was running a bit rich, everything looked ok but it still does it...
-tried making all "overload" and "knocking" tables the same as "normal" in the load targeting section, decreased ignition timing, leaned out AFR from .702 to .77 in .01 increments, still does it...
-I got another log where you can see the "hiccup" pretty clearly and looking at it closer and comparing to what others have reported in other forum posts, I think I'm getting fuel cut.
-I have gone back through every table accessible in VT and dont see anything that would cause this

and this is where I am today. Any feedback would be greatly appreciated. I will attach my latest tune and latest log where the "hiccup" can be seen (IDC drops, requested afr goes up).

Thank you!

Getting an error when trying to attach logs and tune "Temporary folder could not be found or is not writable."

tried uploading from two different PCs, tried uploading individual files and a zip of all of them, tried uploading from different folders including straight from C:\

maybe a permissions issue since I have a relatively new account? Might crosspost to the mazdaspeeds forum...

No, please do not cross post, any change in the forum software that may alter the link will result in broken links.
Upload the logs and tune on some public cloud (google drive, one drive, drop box, whatever) and post the link.

Great idea! Here is two links in case one of them doesn't work

https://drive.google.com/drive/folders/ ... sp=sharing
https://www.dropbox.com/scl/fo/0bvzfylk ... xtjhm&dl=0

Well, load targets set close to 3 and the boost limits set BELOW the stock values will never work hand in hand...

With all due respect, that tune is a total disaster... in every aspect, every bit that was changed...

P.S.: actually I take it back, the MAF calibration seems somehow decent, and the WG duty table seems somehow conservative.

Thanks for the quick response,

This tune is in progress and many parameters were changed in an attempt to troubleshoot the aforementioned issue (which i suspect is fuel cut) including:
-load targets and load limits = 3 across the board
-Overboost Protection Throttle Reduction set to 30 across the board (changed from 30.75-20.16 depending on RPM)
-Overboost Protection Fuel Cut set to 32 across the board (changed from 32.17-12.68 depending on RPM and Baro Pressure)
-"normal" "knocking" and "overload" tables all set the same
-Requested load multiplier Accel/Decel Adjustment all set to 1
-WGDC adjustment limits set to 0
-Ignition timing decreased

I am just trying to remove variables in troubleshooting this issue and have reverted back to BCS DC = 0 and AFR, load, and ignition timing tables to stock values for light load daily driving.

Were you able to see what I'm talking about in the log and any idea what could be causing it? Even if its just a theory or idea, I would be more than happy to adjust the tune and test it out.

So keep in mind that all the boost tables work with absolute manifold pressure, not actual boost. Absolute manifold pressure is Boost + Baro.
In your tune you had all boost limits set lower than the factory which is the reason why you are getting boost cut around 5000rpm. Increasing load limits and targets and lowering boost limits below the factory threshold can only lead to hitting the boost limits which is what you're experiencing.

mituc wrote: ↑August 5th, 2024, 7:02 pm So keep in mind that all the boost tables work with absolute manifold pressure, not actual boost. Absolute manifold pressure is Boost + Baro.

Oh! that makes sense! I was thinking this was a "gauge pressure" reading not "absolute pressure" reading... wow something so simple... thanks!

My immediate reaction was to up throttle reduction to 45 psi (30 psi boost + 15 psi atmosphere) and fuel cut to 47 psi (32 psi boost + 15 psi atmosphere). this is almost double the boost value i was seeing on wastegate spring pressure which is, from my understanding, the theoretical maximum of running a 3 port BCS in WGDC of 100% (https://www.youtube.com/watch?v=hYIL_XvlYTE&t=649s - Driving 4 Answers: Boost School #3).

Prior to doing my build i thought 3 bar MAP = 43.5 PSI boost, ill never hit that - ok ill buy that one. but if MAP reading is "absolute pressure" thats actually a max of 28 PSI. Is that how that works? if so, i should probably set my fuel cut to 42 PSI. And VT recommends setting throttle reduction to ~15% less than fuel cut which would be 36 PSI (or 21 PSI of boost). So it sounds like i need a bigger MAP sensor. Do you see any fault in my logic here?

I will still try out fuel cut = 42 PSI out and report back, i imagine maxing out a MAP sensor to probably induce limp mode.

I have not been logging MAP sensor voltage or pressure, maybe i should in addition to boost.

oh snap, I wonder if thats why I was seeing WGDC drop in the higher RPM before setting BCS DC Adjustment - Decrease from -100% to 0%... more testing required!