05 LGT 5MT - MAF Scaling off ? Log and scaling included

[brok3n potates]

Thanks in advance for the insight, tips and recommendations. Feel free to message me directly or comment below.

 

2005 Legacy GT 5MT

VF52 Turbo - FMIC - AEM320lph Fuel Pump - AEM Wideband O2 - APS 65mm Intake - GrimmSpeed EBCS - Catless DP - 3” Exhaust. Stock injectors, rebuilt engine with stock parts except for Wiseco pistons by previous owner.

 

Checked for vacuum and boost leaks. Vacuum at -18.5 to -19.5 inHg at idle, -22 inHg on deceleration.

 

MAF Scaling much higher than typical ---

 

Tried a more "correct" MAF scaling, and the car starts more correctly, idles fine. Idle AFC +20%, driving AFC +25% or more. Idle AFR on AEM Wideband around 15. Attempt at driving, AFR will go 16-17+ and start breaking up and the engine bucks.

 

Tuned the MAF scaling to closer to what my car wants to run (around 5 g's at idle and somewhat equally higher in higher rpms). The car will start up, but somewhat janky upon startup, bouncing rpm for a second and running rich. AFC -20% at idle, slowly returns itself to +/- around 3-6% (even without Learned AFC). Drives down the road a lot better.

 

But the scaling is much higher than typical scaling for these cars. I don't know if a tiny vacuum leak will skew these readings and scalings this much, but my typical vacuum readings suggest I might not have a vacuum leak, or at least enough of one to cause this ? I could be wrong.

 

Also, previously on my stock tune with edited MAF in the same way, WGDC at 0, I had to scale for approximately 7 g's at idle, which even still, the Logger dashboard read about 4-5 g's at idle, not the 7 ish I had set in the scaling for the same idling MAF voltage.

 

I have included 3 pictures of the MAF Scaling.

Pics are labelled as such, may not be in order:

-05 LGT 5MT Stock MAF Scaling

-05 LGT Stock Tune - MAF Scaling changed by me to be closer to 'correct' running of my car

-Someone Else's Tune - MAF Scaling changed by me to be closer to 'correct' running of my car

Edited March 21, 2022 by brok3n potates

[Pleides]

Have you replaced the MAF sensor on your car? I had to a few years ago due to many MAF issues. Seems like they tend to go sometime after 100K for most people. Might want to start there before you tune the car on a bad sensor.

[Marvick08GT]

Keep in mind if the car was tuned on a low reading or faulty MAF it will need adjustments made to the map.

 

Been there done that, I replace the MAF before tuning now.

[brok3n potates]

You caught me ! lol, no I haven't replaced the MAF yet. Didn't know if that could be the issue. Thanks for the tips, and bare with me I'm new to Subaru's and completely new to tuning as of this year. The car does have 139k miles, and it did sit for some time before I got it, and then about 6 months since I picked it up.

 

Is it a huge concern for me though, if my AFR's, AF corrections etc are tuned properly anyway, regardless of the given MAF values ? Also why would the MAF's actual live readings be different than what I tell it to read ?

^

For example, at say MAF 1.21v, I've changed the g's at that voltage to 6.52 g's... Yet when I'm idling around 1.2v-ish, the g's reading on the dashboard of the logger state around 4-5g's...

 

At this point I'm assuming the MAF is reading less than it should by being dirty, or there is a vacuum leak somewhere that I have yet to find...

 

Also, I know a good tuner would get rid of all knock if possible... How much FBKC, FLKC and Knock Sum is acceptable ? I know Knock Sum can and will increment in situations such as high rpm, low load, shifting etc... But what about cruising and WOT runs, or just in general ?

 

Also, I've been reading up on possibly altering the TIP IN values to accomodate the FMIC, both with having a bit of a lean condition on the start of tipping in (barely hitting gas), as well as kinda rich on Tip OUT... Any tips for that ?

 

I'll link a couple of my WOT logs here, as well as a log just idling after it was driven for about a half hour so it was up to temp etc. The files are named as such for reference.

wot2 32122.csv

wot3 32122.csv

idling 32122.csv

Edited March 22, 2022 by brok3n potates

[Pleides]

Yes, your MAF sensor can exhibit a ton of issues without a major red flag like a check engine light. Mine left a CEL when it failed but many find they unlock a whole new car when they replace theirs. At 139K, if it's original, yes it should be replaced, ESPECIALLY if the car is running an aftermarket intake.

 

If you have a vacuum leak you'll have stuttery power delivery and occasional stalling, or at least a difficult time holding an idle. It might also rev up a bunch when idling for no reason. I'd highly recommend visiting a speed shop that can properly boost leak test your car at higher pressures (10+ PSI).