Fuel Scalar and it's limits (Ethanol)?

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iminhell1

Corporal
Jun 17, 2018
202
So for quite a while I've had my scalars around the 1.4 range. Never really had any problems I knew of. The typical HPFP pressure crashes from time to time and always just above the misfire limit of 700psi.
Late last year I was having more and more pressure drop. Everyone normally attributes this to a failing pump. I wasn't ready to throw in the towel on it. When things fail for me they absolutely fail. Not just go limp a a narrow point.

I'd tuned the car for E50, which I can get at the pump. But when I travel outside my little area I have to play the mixing game, which I don't. I just put E85 in and don't lean on it too much; rely on the stft's to do their job and take care of it. 9 out of 10 times it'll throw a mixture control code, expected. But really I'd though I left enough overhead in the tune that it shouldn't. So I got to thinking, maybe that scalar is playing some part.

So today I changed the target afr to match closer to my scalar x afr. Then knocked the scalar down to 1.25.
To my surprise the car feels better and pressure has come up, dipped down to 6xx for just a split second then jumped to 1,200+ for the rest of the RPM. Right now I'm on almost a full tank of pump E85 (didn't measure actual content).
So something worked here.

My initial thought is that the scalar actually has a hard limit of 1.3. Which would be the 30% limit of STFT's. So a 1.25 would leave me a 5% overhead now.


Has anyone else found something similar? Or am I just dumb and should have known about the scalar limitations.
 

Jeffman

Captain
Jan 7, 2017
1,340
FWIW - I’ve adjusted my scalars in TunerPro when my STFTs were pegging at 34% and I was running too lean in a nearly stock fueling setup on E60. I was able to numerically insert numbers as high as 1.50. Then I upgraded my injectors to index 12 injectors and needed to bring those scalars down quite a bit.
 
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iminhell1

Corporal
Jun 17, 2018
202
Shit my STFT's are maxed at 34% no matter what I do. I've given up on them. I can still use the afr table and it changes logged actual. I try changing the scalar and nothing happens, no change in measured. Only thing I do see change is the rail pressure. When I drop the scalar I gain rail pressure.


If I where smart I'd change the way it's logged and take the gasoline factoring out and convert to Lambda. But I'm not about that simple life. I like complicating and math on the fly.
 

Jeffman

Captain
Jan 7, 2017
1,340
Also keep in mind O2 sensors may also be implicated since they provide the AFR signal which the DME tries to control by changing STFT.
 

jyamona

Captain
Platinum Vendor
Nov 7, 2016
1,069
Philly
Sounds like either rear o2 and lambda sensors need to be replaced, or injectors. I would replace the rear o2's first since they are cheapest, and do all of the fuel/lambda adaptations reset. Then go from there.
 

iminhell1

Corporal
Jun 17, 2018
202
Rear sensors?
I thought all they did after you went catless was input overtemp. The efficiency codes could be ignored.
 

jyamona

Captain
Platinum Vendor
Nov 7, 2016
1,069
Philly
Rear sensors?
I thought all they did after you went catless was input overtemp. The efficiency codes could be ignored.
No, they are directly responsible for characteristic line trimming (adapting / aging) of the main lambdas.
 

veer90

Lieutenant
Nov 16, 2016
931
West Nyack, NY
N54 scalar max is 1.6 in tuner pro.

The term "scalar" in a mathematical sense is a multiplier applied to all terms of an equation or all elements of a matrix. In the N54 it's a multiplier applied to the fuel demand calculation (based on brake specific fuel consumption of gasoline for a stock car). It doesn't exactly correlate with STFTs or anything of that nature, nor can you blanket multiply the scalar based on logs. Best way is to get ballpark values from an experienced tuner then adjust through trial and error.

Increasing the value increases the amount of fuel the car attempts to supply to the motor. Too low, it leans out and trims max, DME is unhappy. Too high, rail pressure crashes, DME is unhappy.
 

iminhell1

Corporal
Jun 17, 2018
202
Well now I'm just confused as shit.
I've been running pump E50 for 2 years now. Worked just fine with the exception of in the 3.5-4k rpm range. Pressure would drop to 800 or lower.

I started playing more with this scalar thing because no one has pump E50 except 3 stations near me. E85 is more readily available and I don't want to play the mixing/guessing game.

I kind of understand what you guys are saying, but that's not how my car has wanted to work ever. Scalar hasn't made any real difference other than with pressure (which I just recently discovered).
So today I started fresh. Loaded the stock target afr tables. Set scalar to 1 across the board. Started the car.
Started out lean, 20's, rough and almost thought it would die out. Once the O2's got some heat (minute about) the STFT's and LTFT's started doing work. LT's max out and afr's came back to target, at idle. STFT's doing the normal trimming.

Changed scalar to 1.2 and redid the idle, stationary rev logging. LTFT's still maxed ... if I'd of been looking at STFT's only I'd of seen normal trimming, 8% variance or so.

Changed scalar to 1.4 across the board. LTFT's came out
25399



And HPFP

25400





Pump has never been this nice in that high load mid rpm.
I kinda wonder if there was something stuck with the HPFP, some learned data that just needed to be shocked out or what. All I know is now things seem to be working as they should again.
dunno
 

iminhell1

Corporal
Jun 17, 2018
202
Ya nevermind.
The SOB learned itself right back to where it was before. Pressure drop in that 3500-4000 range.
 

iminhell1

Corporal
Jun 17, 2018
202
Everything was reset prior to retuning.
I have to go out and rescan and see if I can find what's learning. The nice thing is, I should be able to find what I need to replace, is it injectors or is it hpfp.
Not the progress I wanted but still.
 
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RSL

Sergeant
Aug 11, 2017
395
Is this a DIY tune? Scaled? What torque index array/torque limiter 3? You can tank rail pressure on perfectly good pumps/injectors/O2s even on pump gas if settings don't jive. Ask me how I know lol

Calculated air mass matters for fueling and revving in park isn't the same as driving with boost as far as that goes. Depending what other tables look like, a simple change in VANOS may show improvement in the pressure drop. A quick test would be to retard the intake cam (make the values larger) a few degrees at the usual load you see 3500-3750rpm and see if rail pressure picks up. Hopefully, a few degrees on the cam isn't enough to throw wrench in works for timing, etc.
 

iminhell1

Corporal
Jun 17, 2018
202
I was thinking the same thing with cam timing. I'm using SPxxx's cam files. Have since day one and they work flawlessly.
But for test went back to near stock. Same RPM range for pressure dying out. Cam timing in that area changed about 10*, enough I'd say it should have made some impact. Nope.

I did now notice that LPFP is falling in accordance with the HPFP crashing. I need to see if it's a demand/amperage issue, that maybe I can fix on the cheap (rewire) Or if it's something I should add a 2nd 450 (hobb's and relay).
But the counts for those values aren't very high, and i don't know the polling timing either. Did it drop for a split second @ 10hz? 1 count at a 6 hundredths of a second I can't see being a problem. I do need to log those area's more to get a better idea.


And yes, my diy tune. borrowed parts from others. scaled 3.5bar. only reason i scaled the load was to appease the trans, nice side effect was no post shift timing drop.
It's was working nice for me. dead consistent 11.6's @ 120+. think I have at least 30 from last year and more the year prior. But it's mostly because I work around that 4,000rpm hole I have. LOL
 

Jeffman

Captain
Jan 7, 2017
1,340
I did now notice that LPFP is falling in accordance with the HPFP crashing. I need to see if it's a demand/amperage issue, that maybe I can fix on the cheap (rewire) Or if it's something I should add a 2nd 450 (hobb's and relay).
Have you looked into getting the new BPM LPFP control module?
 

RSL

Sergeant
Aug 11, 2017
395
I was thinking the same thing with cam timing. I'm using SPxxx's cam files. Have since day one and they work flawlessly.
But for test went back to near stock. Same RPM range for pressure dying out. Cam timing in that area changed about 10*, enough I'd say it should have made some impact. Nope.

I did now notice that LPFP is falling in accordance with the HPFP crashing. I need to see if it's a demand/amperage issue, that maybe I can fix on the cheap (rewire) Or if it's something I should add a 2nd 450 (hobb's and relay).
But the counts for those values aren't very high, and i don't know the polling timing either. Did it drop for a split second @ 10hz? 1 count at a 6 hundredths of a second I can't see being a problem. I do need to log those area's more to get a better idea.


And yes, my diy tune. borrowed parts from others. scaled 3.5bar. only reason i scaled the load was to appease the trans, nice side effect was no post shift timing drop.
It's was working nice for me. dead consistent 11.6's @ 120+. think I have at least 30 from last year and more the year prior. But it's mostly because I work around that 4,000rpm hole I have. LOL
10 degrees is a big move, but may take something that hits calcs harder than VANOS or it may just be an actual fueling issue lol I don't run E85, but do know air calc will jack up fuel calcs and rail pressure just as easily as anything else will, which is why I chimed in.

It's nearly impossible to guess what all might be impacting it without seeing the bin and it sounds somewhat like piecemeal as it is, but load matters, as does MAF. If you've had that drop for 2+ years, it's obviously not a crisis, but still betting tuning change would get rid of it.

What does your spool RPM end at out of curiosity?

Have you looked into getting the new BPM LPFP control module?
That thing is nice and makes install/control clean and easy, but the price does leave something to be desired. If you've got $2-3k+ into a fuel system already, I guess it's just another drop in the bucket.
 

iminhell1

Corporal
Jun 17, 2018
202
I'll go 100% DC and return setup before I go with that overpriced controller. They are flat out nuts with pricing.
I don't doubt with a little tweaking a controller from another brand car could work better, be hacked and replace ours. I mean the only downside to ours now is lack of user control and amperage limit. Controller from like a Ford GT, Audi RS cars, Chevy SS/V lineup maybe the ticket?
 

iminhell1

Corporal
Jun 17, 2018
202
inpa won't let me into the ekp. something about looking for ekpm_60.2 or .3 and finding ekp60.
dunno


But I found this:
25434



It looks like something I should pay some attention to.
 

iminhell1

Corporal
Jun 17, 2018
202
Made a single change to the tune and it's gotten better.
load target offset (overboost)

My table was just like every MHD table I can find, most values are 1 and taper as RPM increases.
But looking at JSR tunes, he tends to have it set to 1 everywhere. I can't find a good example of what the table does.
So blindly I changed the whole thing to 1's. Now pressure will drop, it'll miss a little and jumps back to life pretty quick, no lift needed. Before if it missed I had to lift, it wouldn't come out on it's own.

So from what I did find about load target .. it plays into a load adder calculation and it's only supposed to be active in IS codes (overboost). But it's been demonstrated to work in others with tweaks. So I'm thinking something with it worked and reducing with RPM was killing something for me.

And actually the car just all around feels better.
 

Beemin

Private
Nov 5, 2016
41
Los Angeles
Is this a DIY tune? Scaled? What torque index array/torque limiter 3? You can tank rail pressure on perfectly good pumps/injectors/O2s even on pump gas if settings don't jive. Ask me how I know lol

Calculated air mass matters for fueling and revving in park isn't the same as driving with boost as far as that goes. Depending what other tables look like, a simple change in VANOS may show improvement in the pressure drop. A quick test would be to retard the intake cam (make the values larger) a few degrees at the usual load you see 3500-3750rpm and see if rail pressure picks up. Hopefully, a few degrees on the cam isn't enough to throw wrench in works for timing, etc.
I started a thread about this but haven't had much feedback yet, so I figured I'd try bumping this one. Have you run into a situation where you run out of fuel scalar (maxed at 1.6) while all the fuel pumps have more room in them? Happens most often when pushing big power DI only on high concentrations of ethanol, and usually when running a hpfp overdrive upgrade.

There's a great example on a different forum of a dude complaining about his double shotgun not living up to the marketing because his fuel trims and scalar are maxed out at like 22psi on e98, all the while his HPFP was holding strong at 3000psi. He was assuming his injectors were maxed out, but I don't think that's the case. I think it's a tuning problem.

As it sounds like you may be alluding to, I have also noticed a scaled map really pushes fuel trims up (all else being equal), so I'm wondering if there are some workarounds to manipulate MAF calcs to bring those trims back down beyond the BRO table. I haven't noticed huge swings with torque tables or vanos but they do help some. I just feel like with the scaled map making such major changes to fuel trims (as much as 25-30% increase on same boost, same fuel, same scalar for the reduced load, etc) there has to be a way for us to easily move them around as we please.
 

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