RomRaider Logo

RomRaider

Open Source ECU Tools
 FAQ •  Register •  Login 

RomRaider

Documentation

Community

Developers

It is currently Tue Dec 12, 2017 4:29 am

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 19 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: why you can't tune latency via the maf translation table
PostPosted: Thu Mar 12, 2015 10:15 am 
Offline
Senior Member

Joined: Thu Aug 03, 2006 10:40 am
Posts: 1901
for years there have been giant threads on the pros and cons of adjusting injector latency vs tweaking the maf table for fueling errors.

hopefully this post will illustrate why they should not be considered equivalent in terms of outcome.

i have recently turned back to maf tuning after years of speed density. while some things about maf tuning are a pain in the ass, i can safely say that measuring airmass directly (or extrapolating it as the case may be) is a far simpler endeavor than attempting to compensate for the inability to "know" the exact temperature and pressure of the charge air in the chamber.

thankfully, since i have a stock maf sensor in an oem maf tube/airbox, i started with the oem translation table.

i plugged in some sensical value for injector scale and basically started raising latency until idle was stable. i was getting to values that seemed high for what i am running (dark blue wrx injectors with 65psi base pressure), but it was a good starting point, and got the car idling. the latency was much higher than the oem values i had been tuning sd with, but that was part of the reason for switching to maf--to dial in more accurate values for the injectors, and to get better alignment between SD g/s and maf g/s.

then i turned, as so many of us do, to translation table tuning.

i suggest that everyone (maf or sd) tunes open loop exclusively until things are behaving very predictably, as doing so eliminates a confounding effect of the ecu fuel trims chasing their own tail due to latency.

in all fuel tuning a primary metric is some kind of "fuel error." if you run in closed loop you rely on the oem ecu to learn the trims and pump out some numbers. for open loop fueling you don't have trims being determined for you, so you have to define your own.

in my case i've called that term "ve error" because it was used in tuning the VE table, but in any event it is measured afr divided by target afr.. (i also take that number and multiply by 100 to get a percent error, where 100 is perfect, 95 is 5% rich, 105 is 5% lean, and so on. the units are unimportant at this point, as we're interested in trends.)

if we just look at the fuel error vs maf voltage, things look pretty centered around 100%:

Attachment:
File comment: mafv vs fuel error
SNAG-0002.png
SNAG-0002.png [ 65.63 KiB | Viewed 2897 times ]


you would think that latency and scaling tuning was done, and you'd move on to maf table to get things finally dialled in. that's what i thought, and that's what i did.

i quickly realized that despite adjustments i still had excessive errors at certain operating points. after some consideration i realized that there are a great many operating points that will net the same mafv: 10psia MAP/5000 RPM is about the same as 20psia MAP/2500 RPM. you can imagine these equivalent mafvs as diagonal lines from bottom left to top right across a MAP vs RPM surface.

however--and this is the key point--the load (and therefore the IPW) is approximately doubled at the 20psi/2500rpm condition.

since latency errors are IPW based (having the most profound effect at low IPW) this means that the two operating points will have different fueling errors, and adjusting the maf translation table to correct for one will throw off the other. sure enough, this is exactly what i've seen happen.

so how can we visualize this trend? we need to look into another dimension of data. let's first consider RPM as that was one of the variables in the example:

Attachment:
File comment: rpm vs mafv
SNAG-0003.png
SNAG-0003.png [ 55.92 KiB | Viewed 2897 times ]


now it's a lot more obvious that for a given mafv (ie, steady mass flow rate) the fueling error follows a trend that runs leaner at low rpms (where load and therefore IPW is high) and richer at high rpms (where load and IPW is low). what is nice about this way of looking at the numbers is that your maf translation table errors are irrelevant: you are looking for trends while holding mafv steady.

the same data can be visualized by plotting against IPW directly:

Attachment:
File comment: ipw vs mafv
SNAG-0000.png
SNAG-0000.png [ 72.76 KiB | Viewed 2897 times ]


clearly for each row of mafv there's a trend of too rich at low IPW and too lean at high IPW: a classic symptom of latency that is set too high for the injector.

now, why had this latency issue not raised its head in a more obvious way when i was tuning SD? because with SD tuning we DO have a map (volumetric efficiency) that has a tuning axis which represents engine load/ipw, and that is MAP, so we can tune around latency issues. with maf tuning you only have the translation table and that does NOT have a load/ipw reference.

further results to follow...


Top
 Profile  
 
 Post subject: Re: why you can't tune latency via the maf translation table
PostPosted: Thu Mar 12, 2015 5:03 pm 
Offline
Senior Member

Joined: Thu Aug 03, 2006 10:40 am
Posts: 1901
so after reducing latency by 30us (1.16 to 1.13ms) and decreasing the injector scale 3% (from 650 to 630cc/min) i got the following data from the drive home:

Attachment:
2015-03-12_16-37-29.png
2015-03-12_16-37-29.png [ 39.62 KiB | Viewed 2882 times ]


driveability is noticeably improved, but the error still isn't level across each row, especially at very low ipw.

i will take it one more step with the same deltas and see how it runs in the morning.


Top
 Profile  
 
 Post subject: Re: why you can't tune latency via the maf translation table
PostPosted: Mon Mar 16, 2015 5:01 pm 
Offline
Senior Member

Joined: Thu Aug 03, 2006 10:40 am
Posts: 1901
after quite a few more iterations, i have arrived at some values i think are much closer to empirical latencies (at least at running voltage):

v,ms
6.50,2.93,
9.00,1.61,
11.50,1.02,
14.00,0.68,
16.50,0.54,

yes, that is LOWER than oem values for 07wrx injectors.

i'm as surprised as you are, but at least now the fuel correction per mafv has no slope wrt ipw. that's good enough proof for me.

what is nice about this method for tuning latency is that it can be continually monitored on daily drives, and adjusted as necessary.


Top
 Profile  
 
 Post subject: Re: why you can't tune latency via the maf translation table
PostPosted: Tue Nov 17, 2015 8:31 pm 
Offline
Newbie

Joined: Wed Mar 21, 2012 6:45 pm
Posts: 66
Hmm, I'll have to try this out. I've always thought that my "open scatter" to my mafv vs fuel error was caused by latency being off.... Instead I corrected it with EL comp. Just curious as to what was in your EL comp table at the time of this?


Top
 Profile  
 
 Post subject: Re: why you can't tune latency via the maf translation table
PostPosted: Mon Dec 21, 2015 3:07 pm 
Offline
RomRaider Donator

Joined: Thu Jan 29, 2009 11:16 am
Posts: 523
nxm08240 wrote:
Hmm, I'll have to try this out. I've always thought that my "open scatter" to my mafv vs fuel error was caused by latency being off.... Instead I corrected it with EL comp. Just curious as to what was in your EL comp table at the time of this?


If he is still running Carberry, there is no EL comp table. At least in the version I am using...

_________________
Mods: http://www.romraider.com/forum/viewtopic.php?f=7&t=6789&start=5


Top
 Profile  
 
 Post subject: Re: why you can't tune latency via the maf translation table
PostPosted: Tue Dec 22, 2015 12:23 pm 
Offline
Experienced

Joined: Mon Jun 01, 2015 9:15 pm
Posts: 100
Location: Albuquerque New Mexico
So if I want to attempt to log and tune this, I need to log wb02, rpm, mafv, IPW direct, and FFB? This is super neat and I think this will help me a lot.

Do the % error on the fuel from the (wb02/FFB)*100=fuel error where less than 100 is rich and more than 100 is lean.

make tables where: rpm vs mafv with the fuel error plotted
: ipw vs mafv with the fuel error plotted

Both tables are similar information just different ways of seeing it?
adjust latency's till the error is consistent across the entire range of the tables?

To much latency you will see rich is the upper left of the table and lean in the lower right? To little would be the opposite?

thanks
Chris

_________________
2001 RS 2.5 w/ 2002 harness and dash swap 2001 jdm ej205 w/avcs


Top
 Profile  
 
 Post subject: Re: why you can't tune latency via the maf translation table
PostPosted: Mon Jan 11, 2016 4:52 pm 
Offline
Newbie

Joined: Tue Jun 07, 2011 5:34 pm
Posts: 35
Location: Oregon
Ride5000, what software do you use to translate columns of MAFV, IPW, and error together?

_________________
Daily Driver: 2008 Subaru Outback XT
DW850cc Injectors, DW65c Fuel pump
Coated Cobb Catted Downpipe, PLX AFR Wideband


Top
 Profile  
 
 Post subject: Re: why you can't tune latency via the maf translation table
PostPosted: Mon Jan 11, 2016 5:07 pm 
Offline
Senior Member

Joined: Thu Aug 03, 2006 10:40 am
Posts: 1901
flinkly wrote:
Ride5000, what software do you use to translate columns of MAFV, IPW, and error together?

that's ecuedit.

not free, but absolutely worth the cost imo.


Top
 Profile  
 
 Post subject: Re: why you can't tune latency via the maf translation table
PostPosted: Mon Jan 11, 2016 5:39 pm 
Offline
Newbie

Joined: Tue Jun 07, 2011 5:34 pm
Posts: 35
Location: Oregon
ecuEdit standard edition?

http://www.epifansoft.com/ecuEdit-versions-prices.html

i wish Minitab would make my tables, but it won't cause "..over 40% of the cells are empty."

_________________
Daily Driver: 2008 Subaru Outback XT
DW850cc Injectors, DW65c Fuel pump
Coated Cobb Catted Downpipe, PLX AFR Wideband


Top
 Profile  
 
 Post subject: Re: why you can't tune latency via the maf translation table
PostPosted: Mon Jan 11, 2016 6:40 pm 
Offline
Newbie

Joined: Sun Jul 13, 2014 6:12 pm
Posts: 80
This would work:
viewtopic.php?f=32&t=10481


Top
 Profile  
 
 Post subject: Re: why you can't tune latency via the maf translation table
PostPosted: Tue Jan 12, 2016 10:19 am 
Offline
RomRaider Developer

Joined: Wed May 20, 2009 9:49 pm
Posts: 5659
Location: Canada eh!
You can also use any spreadsheet app that has Pivot Table support.


Top
 Profile  
 
 Post subject: Re: why you can't tune latency via the maf translation table
PostPosted: Tue Jan 12, 2016 11:58 am 
Offline
Senior Member

Joined: Thu Aug 03, 2006 10:40 am
Posts: 1901
there are of course an infinite number of ways to achieve the same results. :) a savant could just look at the numbers and give you an answer!

after a decade of fits and starts i just went ahead and bought ecuedit so that i could concentrate on tuning rather than messing around with the tools.

ecuedit is far from perfect but i found it to be an amazing tool for analyzing and manipulating log data and incorporating those results directly into the rom.

(i do not use it for log capture as it does not have support for my wideband. and no, i am not compensated by epifan in any way.)

jm2c
ken


Top
 Profile  
 
 Post subject: Re: why you can't tune latency via the maf translation table
PostPosted: Tue Jan 12, 2016 1:24 pm 
Offline
RomRaider Donator

Joined: Thu Jan 29, 2009 11:16 am
Posts: 523
I do a lot in excel and I like the flexibility it offers with the VBA, but for quick analysis, I find myself using ecuedit more and more. Just wish I could find a way to filter based on previous rows (change over time).

_________________
Mods: http://www.romraider.com/forum/viewtopic.php?f=7&t=6789&start=5


Top
 Profile  
 
 Post subject: Re: why you can't tune latency via the maf translation table
PostPosted: Wed Jan 13, 2016 4:33 am 
Offline
Newbie

Joined: Sun Jul 13, 2014 6:12 pm
Posts: 80
ride5000 wrote:
ecuedit is far from perfect but i found it to be an amazing tool for analyzing and manipulating log data and incorporating those results directly into the rom.


This is why I suggested the above, it has most if not all of the benefits of Ecuedit but is free. Admittedly I have to manually add a couple of columns in my logs but that takes less than a minute if your logs have the same column layout and then I can get results like yours above:
Image

and then, for example, quickly change to see where I get FBKC in my timing tables:
Image


Top
 Profile  
 
 Post subject: Re: why you can't tune latency via the maf translation table
PostPosted: Wed Jan 13, 2016 6:47 am 
Offline
Newbie

Joined: Wed Jun 06, 2012 10:11 pm
Posts: 25
Thanks ride5000... you've described exactly a problem I've been having...

I went to the effort of putting the stock airbox back in, the stock MAF scaling and Rom Raider's "Injector" tab to get my injector scaling spot on (or so I thought?).

I have since spent SO many hours trying to get my MAF scaling right - but I just can't seem to tame it. I've got the long term trims setting nicely, but the short term trims are all over the place.

Here's where I was getting at with the Engine Load comp (using Airboys spreadsheet... shows manifold pressure vs fuel corrections). As you can see it's pulling heaps of fuel at low RPM's towards 0psi, and adding heaps of fuel at higher RPM's but low boost..

Image

My current injector latency is:
v 8.0 10.0 12.0 14.0 16.5
ms 2.6 1.58 1.17 0.88 0.69

My current injector flow scaling is 860 (for 1000cc Denso injectors).

I suspect I an issue with the injector scaling (similar issue that you had)... but I can't really work out what I need to do next try and fine tune my injector scaling/latency...

Would tweaking the MP Compensation table be a "hack" way to sort it? I don't have any major driveability issues - I'm just bugged by the short term fuel trims.

Cheers,
Kim


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 19 posts ]  Go to page 1, 2  Next

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Style based on FI Subsilver by phpBBservice.nl