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Old 12-10-2011, 09:40 PM   #1
faeflora
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I have a pile of parts and a tactrix cable. I've tuned Hydra and Megasquirt before but am unfamiliar with this opensource MAF stuff. Here's my parts pile:

2004 Forester XT Automatic
VF48
Nvidia catted DP
3" exhaust
agency power metal intake pipe (not short ram, stock replacement)
sti TMIC
sti uppipe
stock injectors
PLX DM-6 wideband

I read a bunch of stuff but still have some questions:

How do I "tune fuel"? From what I understand, do I just adjust the MAF Sensor Scaling until my AFR gauge matches up with the targets in my Primary Open Loop Fueling table?
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Old 12-11-2011, 10:12 AM   #2
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Old 12-11-2011, 12:00 PM   #3
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That didn't answer my question. I read the guide twice. I'm just looking for the explicit answer- yes or no.
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Old 12-11-2011, 01:59 PM   #4
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The answer is yes and no. All that matters is what AFR comes out the tail pipe. You can do that in several ways. You can manipulate the MAF scaling,or the openloop table and even injector scalings. Generally you want to rescale the MAF until fueling corrections are -/+ 5%, but it's not 100% " black and white" this has to be done. "Tuning fuel" is tuning ALL the fueling tables,not just the MAF table. Obviously tuning fuel would also incorperate changeing the factory calibration open loop AFR's as well since from they are pig-rich.
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Old 12-12-2011, 04:49 PM   #5
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Quote:
Originally Posted by faeflora View Post
How do I "tune fuel"? From what I understand, do I just adjust the MAF Sensor Scaling until my AFR gauge matches up with the targets in my Primary Open Loop Fueling table?
Basically yes. I set the OL table to 11 at wot then adjust the MAF to get there.

The major difference between the different methods is that changing the MAF scale changes the loads, which can effect all load based tables in the ecu.

So when you're scaling the OL portion of the MAF and you add 5%, all your load values are gonna go up.....so you may have just disabled your knock control, or be close to a load limt, or be riding the high load column in the timing and fueling table....

when you're changing the MAF scale you really need to think about how the Load is gonna change.

MAF based is not much different from MAP. Instead of MAP vs RPM tables its just Load vs Rpm and the load is calculated from the MAF via

Load = (MAF(g/s)*60)/RPM
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Old 12-13-2011, 01:10 AM   #6
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Three things to add...

First, there are spreadsheets and tools for dialing in the MAF scaling in both open-loop and closed-loop modes. I prefer to force the ECU to run open loop (details here). That you can use one method to dial in the whole MAF scaling from top to bottm.

Second, that one method is just a fairly simple Excel spreadsheet. Given a data containing your real AFR (from a wideband sensor) and the ECU's target AFR (from the "final fueling base" parameter), make an "AFR Error" column (= real_AFR / target_AFR). Then make scatter plots of error over MAFv and error over RPM. Everything I know about Excel I learned from trying to visualize the information in my data logs. Learning Excel was a fringe benefit of learning tuning.

Third, generally you only need to look at error over MAFv, but occasionally you'll find places where the same MAFv corresponds to both positive and negative errors, depending on RPM. You can fix that by fudging the fuel table values, and I did for a while, but I now prefer to have the fuel table contain the AFRs that I really want, and use the "Engine Load Compensation (MP)" table to fix issues that crop up in certain areas.
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Old 12-13-2011, 01:42 AM   #7
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^ trying to scale my maf in open loop doesnt work at all. it runs really rich. like 13.0 at idle and 13.5 cruising, if i correct the MAF then go back to closed loop i have huge corrections.

ive also tried running without the front 02 sensor in SD mode and it doesnt work at all either.
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Old 12-13-2011, 09:18 AM   #8
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Quote:
Originally Posted by Phatron View Post
^ trying to scale my maf in open loop doesnt work at all. it runs really rich. like 13.0 at idle and 13.5 cruising, if i correct the MAF then go back to closed loop i have huge corrections.

ive also tried running without the front 02 sensor in SD mode and it doesnt work at all either.
^^^ I've also tried to scale the closed loop portion of the maf scale in open loop. Then only end up with large corrections when closed loop is enabled. So I don't think that method really works. I've tried it on 16 bit and 32 bit, maf and SD.
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Old 12-13-2011, 11:39 AM   #9
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Thank you everyone, your posts have helped a lot and I feel like I'm getting pretty close to being able to tune my car successfully.

When I alter the MAF Sensor Scaling table, do I want to alter the sensor volts AND the airflow, or just the airflow? I thought that the MAF was only 0-5v but the voltage can go higher in the software.


Quote:
Originally Posted by NSFW View Post
Three things to add...

First, there are spreadsheets and tools for dialing in the MAF scaling in both open-loop and closed-loop modes. I prefer to force the ECU to run open loop (details here). That you can use one method to dial in the whole MAF scaling from top to bottm.
I agree, that sounds like a much more accurate way to tune my closed loop MAF- in open loop. Thanks!


To me, it looks like the easiest and most reliable way to tune fuel (without messing up any other load tables) would be to use the Engine Load Compensation (MP) table. Looking at the map though, there is not much resolution for boost. I only have two columns. Will it work if I reduce the number of vac columns and add more boost columns?

Like this


Original


Altered
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Old 12-13-2011, 03:23 PM   #10
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Originally Posted by faeflora View Post
When I alter the MAF Sensor Scaling table, do I want to alter the sensor volts AND the airflow, or just the airflow? I thought that the MAF was only 0-5v but the voltage can go higher in the software.
Well, the g/s is what changes the fueling. So that is the parameter you need to be modifying.

The MAFv only needs to be modified if you want more fidelity in a certain voltage range or if you're gonna be flowing more than 4.69 MAFv (the stock scale only goes to 4.69), then you need to extend the scale out further.
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Old 12-14-2011, 12:58 AM   #11
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Quote:
Originally Posted by Phatron View Post
^ trying to scale my maf in open loop doesnt work at all. it runs really rich. like 13.0 at idle and 13.5 cruising, if i correct the MAF then go back to closed loop i have huge corrections.

ive also tried running without the front 02 sensor in SD mode and it doesnt work at all either.
Quote:
Originally Posted by fastblueufo View Post
^^^ I've also tried to scale the closed loop portion of the maf scale in open loop. Then only end up with large corrections when closed loop is enabled. So I don't think that method really works. I've tried it on 16 bit and 32 bit, maf and SD.
Weird, I haven't run into those problems.
What method are you guys using to force open-loop?
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Old 12-14-2011, 01:15 AM   #12
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To me, it looks like the easiest and most reliable way to tune fuel (without messing up any other load tables) would be to use the Engine Load Compensation (MP) table. Looking at the map though, there is not much resolution for boost. I only have two columns. Will it work if I reduce the number of vac columns and add more boost columns?
You're going to affect other load-based tables regardless of which table you use to make your fueling adjustments. Suppose your ECU thinks it's pulling 2 g/rev at 4000 RPM in the middle of a pull... if you add 10% to the corresponding cell in the MAF scaling, it's going to think that it's pulling 2.2 g/rev under the same circumstances. Or if instead you add 10% to the corresponding cell in the Load Compensation table, it's still going to think that it's pulling 2.2 g/rev under the same circumstances. Either way it will start using the fueling and timing from cells slightly to the right of the ones it was using before, even though the actual load is exactly the same.

Your corrections may not actually be 10% but you get the idea.

To reduce AFR errors that consistently correspond to a particular MAF voltage (regardless of RPM or load), adjust the MAF scaling. To reduce AFR errors that correspond to a particular load and RPM (regardless of MAF voltage), adjust the Load Compensation table.

And yes, you can revise the row and column values if you want. My columns run from -10 to +22, and they're not evenly spaced but they give me resolution where I needed it.
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Old 12-14-2011, 01:30 AM   #13
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Cool, thank you. I'm picking my car up on Thursday with the new turbo and exhaust and I'm guessing that due to the stock injectors and intake my closed loops will look pretty good.

To tune boost I was thinking of running on wastegate pressure to see how the AFRs look and log and then.... look at the MAF load and AFR and adjust accordingly. I can do the arithmetic to determine how much I need to adjust MAF load for the given voltage by looking at the AFR error percentage.
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Old 12-14-2011, 02:01 AM   #14
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Weird, I haven't run into those problems.
What method are you guys using to force open-loop?
Exactly how u do....0 the delays and make the min enrichment 14.6
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Old 12-14-2011, 02:25 AM   #15
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That's pretty much how it works. Make the corrections about half of what the math suggests though, and plan to do a few iterations. The data is pretty noisy so if you try to fix it in one shot you'll just end up putting noise into your tables.

When you start turning up the boost, it's good to do pulls at wastegate boost and high boost so that you can look at data from both. If they don't have similar errors at similar MAFv, that's when you need to use the Load Compensation table.

Also, multiplying the "Knock Correction Advance Max" table by 50% will give you some extra safety margin. I tend to do that when I'm making changes that might have surprising side-effects, and if you're new at tuning, just about everything might have surprising side-effects.
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Old 12-14-2011, 02:32 AM   #16
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Exactly how u do....0 the delays and make the min enrichment 14.6
Weird. I wonder what's different about your ECU vs. mine.
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Old 12-14-2011, 03:39 PM   #17
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Exactly how u do....0 the delays and make the min enrichment 14.6
This is how I also forced open loop. I also have used the warm up enrichment table ect to keep ecu at 7 for cl/ol status. Still had same results.
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Old 12-14-2011, 06:38 PM   #18
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Weird. I wonder what's different about your ECU vs. mine.
Idk. I dont see any defined compensations in the rom that would be causing it. I tried it twice. Scaling the MAF in closed loop my corrections are +-3% and the interpolation line in MAF tabbing is right on zero. If i use that scale and go to full time OL, it is rich everywhere. If I then scale it in OL and go back to closed loop the corrections go to 10-15%.
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Old 12-15-2011, 10:05 AM   #19
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Good thread guys! There is a lot of info here.
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Old 12-22-2011, 02:59 AM   #20
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OK after about 2 hours I got my AFRs looking pretty decent. It was pretty straightforward.


I didn't use the log and spreadsheet, I just did the math and adjusted the MAF smoothly while watching my AFRs. They are sitting at 11.3-11.7ish which should be fine since I didn't touch the factory timing map. After I get my wideband sensor logging properly I'll tune it in some more. I also zeroed out the open/closed loop transition times and also reduced the throttle position closed loop threshhold which made the car much peppier.

Open loop was just fine and sitting around 14.5-14.7. I'll see how the gas mileage is and will maybe try to set up lean cruise.

I'm on the stock solenoid which is hitting 20psi but sags to around 15. I'm not looking forward to tuning the PID crud. With the 3" exhaust I'd think there is the volumetric efficiency to hold 18psi to redline.

One boost issue I have is that between gears (I have an automatic), boost seems to take a bit longer to build than I think it should. I think it's a boost control thing and not boost onset/spool since this is a baby VF48.

Car is quite a bit more ballsy now. Nothing close to the insanity of my miata but it really does haul off the line in 1st and gets to 100mph pretty quickly.
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Old 12-22-2011, 11:29 AM   #21
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A lean afr must be fine since youre running factory timing? Unless u have an egt gauge u should really keep the afr ~11

U put on a turbo that's way bigger and youre running way more boost than stock, you need to change the load columns and the timing

Zeroing the delays is just gonna make your gas mileage worse.

Don't analize about the pid loop. Just cut the factory turbo dynamics values in half. For the max wgdc just run a flat map of whatever makes u hit 20psi. So if it takes 70% to hit 20psi just make the whole
Max map 70, then make the initial map 60 flat. Done.
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Old 12-22-2011, 11:46 AM   #22
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Here is a tutorial I wrote a while back on dialing in base maps: http://msioc.com/forums/viewtopic.php?f=23&t=266

There is a section on maf scaling in there that might help a little. However, it is a tad outdated as I have learned quite a bit more about our ecu's since then. I usually start by getting the CL portion dialed in really well with the maf tab in romraider. During every iteration, check the graph of your maf table in ECU flash to make sure it is a smooth curve. Sometimes its hard to hit certain spots in the MAF table. If you get certain spots dialed in really well, but theres a bump in the curve caused by a spot that has not been adjusted due to lack of data, you can usually just use some interpolation in ECU flash. Another way to do this, as well as smooth out your curve, is to graph your maf curve in excel, and then add a polynomial trend line, setting it to 5 or 6. Check the box that says "display equation on chart". You can enter this equation into wolframalpha.com and have it solve for the g/s value at the voltage point that lacks data. I am sure theres an easier way to do this in excel, but I'm no excel genius.

Once I have the CL portion complete, I then use a combination of the OL spreadsheet, and manual analysis inside airboys spreadsheet's afr interpolate tab. Fast polling has made this process WAY easier than it used to be. Another thing I do is graph logged WBO2 data compared to final fueling base, as NSFW mentioned. This is still a pretty gray area in subaru ECU's, but it will give you an idea of whether your maf scaling is off in a spot, or if your ecu is just acting on your target AFR's.

Once I get the OL portion within +/- 2% error in WOT, I move on to the engine load comp table by using this spreadsheet: http://www.romraider.com/forum/viewt...hp?f=32&t=5483

If I notice a correlation in AFR error outside +/-2%, and varying IAT's, I then touch everything up with the maf IAT comp table.

Last edited by D0nets; 12-22-2011 at 12:00 PM.
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Old 12-22-2011, 12:20 PM   #23
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Originally Posted by Phatron View Post
A lean afr must be fine since youre running factory timing? Unless u have an egt gauge u should really keep the afr ~11

U put on a turbo that's way bigger and youre running way more boost than stock, you need to change the load columns and the timing

Zeroing the delays is just gonna make your gas mileage worse.

Don't analize about the pid loop. Just cut the factory turbo dynamics values in half. For the max wgdc just run a flat map of whatever makes u hit 20psi. So if it takes 70% to hit 20psi just make the whole
Max map 70, then make the initial map 60 flat. Done.
Why would I want to halve the factory turbo dynamics? To make it respond more slowly?

Also, I don't have the option to log Feedback Knock Correction. I guess this is because it's not in my 04 automatic ECU?
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Old 12-22-2011, 12:44 PM   #24
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Originally Posted by faeflora View Post
Why would I want to halve the factory turbo dynamics? To make it respond more slowly?

Also, I don't have the option to log Feedback Knock Correction. I guess this is because it's not in my 04 automatic ECU?
It is probably there, just not in the logger definitions. Post on the romraider forums to have someone help add it to your defs.
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Old 12-22-2011, 01:15 PM   #25
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Why would I want to halve the factory turbo dynamics? To make it respond more slowly?
yes. it dampens out boost oscillations.

if you set the turbo dynamics aggressively then your boost curve is gonna look like a saw blade AND you're gonna boost spike bad in higher gears.

what i do is set the target boost to 0.25 psi higher than i want the car to run....so say i wanna run 20...set target boost to 20.25, then setup the max wgdc so that you only hit 20. The flat wgdc acts as a boost cap kinda like a mbc. so now you'll run 20psi and the turbo dynamics wont even really matter because you're never hitting target boost...so they dont start pulling wgdc on you and oscillating boost.
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