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Old 07-24-2007, 12:03 PM   #1
akira02rex
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Default Ok I'm stumped - AFR's way off of target

Mods:
-td05-20g turbo
-perrin silicone inlet
-sti tmic
-3in tbe
-perrin up-pipe
-stock air intake box w/ perrin replacement filter
-modded stock injectors

I had the engine tuned by modifying the MAF table recently which worked out pretty well. I then saw that MRF came up with the idea to switch back to a bone stock maf table and change latency/injector scale only so I went with his settings.
The values he provided work great; my ltft and stft are within +/- 4% cruising around town so that's good to go.

I decide to do a short pull and check out my fuel targets at WOT.
My fuel target was 8:1 and I get:

4000rpm = 10.9:1
5000rpm = 11.6:1
6000rpm = 12.1:1

It was only a 2nd gear pull and EGT's rose to 1660F which isn't TOO bad.

As you can see, as the rpm's/maf go up, the engine runs leaner and my fuel map is targeting 8:1 in all of that area.


Another problem:
I also noticed something is wrong with the tip-in enrichment which I have never messed up before; it's all stock mapping.
When I rev up the rpm's or when I take-off from a standstill I can feel the engine stutter a bit.
I checked out the AFR as it did this and it seems to go rich, down to 13:1. I think the changing the injector latency messed with this.
Any ideas??
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Last edited by akira02rex; 07-24-2007 at 12:18 PM.
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Old 07-24-2007, 12:21 PM   #2
Master2192
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I don't see a upgraded fuel pump on the list above, have you upgraded the pump or not?
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Old 07-24-2007, 12:25 PM   #3
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Quote:
Originally Posted by Master2192 View Post
I don't see a upgraded fuel pump on the list above, have you upgraded the pump or not?
Sorry, yes it's a walbro 255.
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Old 07-24-2007, 12:27 PM   #4
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Also, on the tip-in issue. When you install bigger injectors you should modify the tip-in table. I usually do a percentage adjustment and it seems to work perfect. Not sure what your injector scaler is, but mine ended up being 830cc. 420/830 = 50.6%, so I selected all the tip-in values in enginuity and multiplied them by .506

Car drives like stock.
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Old 07-24-2007, 12:30 PM   #5
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Quote:
Originally Posted by akira02rex
Sorry, yes it's a walbro 255.
Hmm, I am not sure then. The lean out looks like either fuel pressure is dropping off or you are maxing out the MAF sensor. I just maxed out the MAF voltage on a 16g, can't imagine what you are doing.

Can you provide any logs? I would like to take a closer look.
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Old 07-24-2007, 12:50 PM   #6
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Quote:
Originally Posted by Master2192 View Post
Hmm, I am not sure then. The lean out looks like either fuel pressure is dropping off or you are maxing out the MAF sensor. I just maxed out the MAF voltage on a 16g, can't imagine what you are doing.

Can you provide any logs? I would like to take a closer look.
Funny you say that lol.
My max mafv in 90* weather right now is around 4.5 - 4.55volts.

Also, I just fixed my tip-in exactly like you stated above before I even read what you posted; I read up on how to do that over at enginuity.org.
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Old 07-24-2007, 02:45 PM   #7
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I'm just going to adjust my fuel map. I'm down in the 6's for my target at redline, but what can ya do?
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Old 07-24-2007, 03:31 PM   #8
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How exactly did you go about tuning the injector size? I an unfamiliar with the MRF way, what I did was tuned the injector size until AFRs matched what the fuel map said. And then adjusted latency to get startup and fuel trims correct.

btw the lowest AFR you can put in the fuel map is 4.91, so you are running out of room to adjust it richer.
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Old 07-24-2007, 07:05 PM   #9
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what do your injector latency vaules look like?

edit: NVM, comphrehension pwnzs me tonight.
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Old 07-25-2007, 03:12 PM   #10
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Quote:
Originally Posted by akira02rex View Post
I'm just going to adjust my fuel map. I'm down in the 6's for my target at redline, but what can ya do?
something is seriously wrong with your Inject scale & latency. please list what your scale is & latency.
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Old 07-26-2007, 02:42 AM   #11
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just of curiosity u said ur egt were at 1660 and thats not to bad?

r u smokin something?
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Old 07-26-2007, 09:49 AM   #12
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Quote:
Originally Posted by ol'skoolwrx View Post
just of curiosity u said ur egt were at 1660 and thats not to bad?

r u smokin something?
It isn't out of the realm of being OK. There are many people who shoot for that number, but I like to be at 1600F or under.

The injector scale is 835 and the latencies are from MRF's thread "circumsized stock injectors". He made the thread a long time ago and the values have worked for many people. My stft/ltft are actually very very good with his values but I have had an afr target problem way long before this. I do not think the problem lies within my latency and injector scale size.
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Old 07-29-2007, 10:28 AM   #13
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cut and paste without understanding what you're doing
will cause odd problems..

yes there are a ton of people who have a "map"
but more than not their car is not the same as
your car.

not flaming anyone but do your homework and
comprehend then tinker..
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Old 07-30-2007, 09:57 AM   #14
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Sounds like you need to do your homework.
If every vehicle Subaru put out then, I guess they'd all have their own map because technically, every car is different.

The maps MRF derived are for a stock air box and modded injectors.
For slight variances, as in the case for factory vehicles there is A/F LEARNING and CORRECTION.

I hate ignorant people...
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Old 07-31-2007, 04:33 PM   #15
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Are you still running the stock MAF scale?

Quote:
Originally Posted by akira02rex View Post
Mods:
-perrin silicone inlet
-sti tmic
-stock air intake box w/ perrin replacement filter

As you can see, as the rpm's/maf go up, the engine runs leaner and my fuel map is targeting 8:1 in all of that area.

Any ideas??
All of these will change the amount of air entering the engine and you have done nothing to tell the car this.

I am still tuning out the entire MAF scale on my car just for an intake at the moment and my LTFT is 3% or less.

-Rene
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Old 07-31-2007, 09:46 PM   #16
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Quote:
Originally Posted by Rene2.5RS View Post
Are you still running the stock MAF scale?



All of these will change the amount of air entering the engine and you have done nothing to tell the car this.

I am still tuning out the entire MAF scale on my car just for an intake at the moment and my LTFT is 3% or less.

-Rene
well the stock acceptable range +/-14% for both stft & ltft
so you did a good job
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Old 08-01-2007, 02:16 AM   #17
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Thanks. I take pride in ensuring my car is running the best that it can. Here is a short example from tonight. This is while the car is at idle at full operating temp at a MAF volt of 1.40:

STFT
Before 0.78, 0.78, 0.78, 1.56, 1.56
After -0.78, 0, 0, 0, 0

LTFT
Before 4.69, 4.69, 4.69, 4.69, 4.69
After -1.56, -1.56, -1.56, -1.56, -1.56

Side not while at idle in the lower MAF volt range it is better to have fuel being removed than being added.

Sorry for the hijack. akira02rex if you want some help scaling your MAF send me a PM.

-Rene
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Old 08-01-2007, 04:25 AM   #18
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there's no need to rescale a MAF. It's a band aid to the correct way of tuning it out.

Akira, I'd start to play with your latency value because something is very wrong there. How's the car drive during closed loop? Sounds to me like you've got a post MAF leak under boost.
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Old 08-01-2007, 09:05 AM   #19
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I agree. The only reason to change the MAF table is for an intake change.

Modded stock injectors can be hard to tune IMO simply due to the variance in flows, among other reasons.
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Old 08-01-2007, 09:29 AM   #20
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Well, I think I have found the culprit:

This is before I decided to go the inj. scale/latency tuning route:
1. Before I modified the maf table and my inj scale was 783cc - once again, from mrf and it worked flawlessly. I also had to rescale the upper end of the maf table for even more fuel. I was hitting 300g/sec at only 4.5mafv to achieve the fueling I needed for my 20G.

2. I modified the stock BPV by drilling a hole in the sidevent tube and plugging it underneath which is determined to hold a ****-load of boost.
^- One thing I noticed though and MIGHT be throwing my afr off is - when I first installed the bpv I left the bpv return line unhooked and the engine ran like complete crap. I noticed that it was leaking?! I then hooked up the return line and all was well because the "leak" from the bpv was "recycled" back into the intake.

Now that I think of it though, if I am under boost pressure, then this leaked air is going right back into the intake. This could be measured as unmetered air if I am not mistaken. It WAS metered at one point, but it's being recycled if you will, back into the turbo and causing me to lean out even more.

OR...is this bpv leak just compensating for what is basically a boost leak?

Some basic math I did of my fueling of my old rom tune compared to my new one:

I calculated that before I was adding in 40% more fuel via afr target, maf scale, inj. scale value.

Now, take my current afr target 6:1 and divide by my current actual = 11.7:1 and you get close to 40%. And a little more for the previous rom may be contributed to the fact of the bpv theory I mentioned above.

I think I need to put my perrin bov back on and switch to my old method of tuning...
Even though people must say it is the wrong approach..it DID however work much better.
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Old 08-01-2007, 02:15 PM   #21
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You will have to explain this leak to me a bit more, both the Perrin and the stock BPV are designed to "leak" or otherwise be open at idle. The air never leaves the system so it does not cause you to run lean, its all after the maf. Just because it is recirc'd back before the turbo does not mean it is suddenly unmetered air.

What you need to do to get the AFR targets to match real world is:
1.Use the STOCK injector scaler, but with the proper latency values.
2. Rescale the entire maf table, you can usually start of by multiplying the whole table by the percentage difference between the injector scale and true injector size. I'll assume that you know how to rescale maf.

If you do it right, all of your AFR targets in the map will be identical to real world AFR. This is the only way to get past the 300 g/s limit as of now.
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Old 08-01-2007, 02:42 PM   #22
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Quote:
Originally Posted by HndaTch627 View Post
there's no need to rescale a MAF. It's a band aid to the correct way of tuning it out.
How can you say that scaling the MAF table to the correct amount of air entering the engine is a band aid fix.

Say for example you drop a new panel high flow panel filter into the air box (something the OP did) why would you call this a high flow panel filter, because it flows more air. Lets see now add a smoother and higher flowing turbo inlet and you get more air enterig the engine. Do you see what is happening here yet. You know have more air entering but the ECU does not know this so the old amount of fuel isn't enough. To correct this you rescale the MAF table so the ECU knows exactly how much air is entering so it can properly achieve your target AFR. You do not richen up your fuel map to do this, that would be the band aid fix.

If you tune for a target AFR of 6:1 to actually achieve 11:1 you need to start over. Period.

Follow what Master2192 said and if this doesn't work let us know and maybe provide some logs so we can look further into this.

-Rene
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Old 08-01-2007, 02:45 PM   #23
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I went back to a 783cc inj. scale with mrf's maf table down low for good fuel trims at idle and cruising. I left the latency values stock as well.

I then took a couple a/f logs and modified the table up top to match target and actual a/f. I also have the 400g/sec rom fix which I mapped out to 400g/sec for security .

Car runs perfect now and I decided to hook up my trusty MBC and I'm keeping 20.6psi all the way to redline...maybe I'll turn it up some more .

People may say this is the incorrect approach of tuning the engine, but it sure does work well for me.
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Old 08-01-2007, 03:02 PM   #24
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Quote:
Originally Posted by akira02rex
People may say this is the incorrect approach of tuning the engine, but it sure does work well for me.
Personally, I would say anyway that gives you good timing/afr values is the correct way regardless of what anyone says. If the car starts and drives like stock, then I accomplished my goal.
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Old 08-01-2007, 03:34 PM   #25
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Quote:
Originally Posted by Rene2.5RS View Post
Say for example you drop a new panel high flow panel filter into the air box (something the OP did) why would you call this a high flow panel filter, because it flows more air. Lets see now add a smoother and higher flowing turbo inlet and you get more air enterig the engine. Do you see what is happening here yet. You know have more air entering but the ECU does not know this so the old amount of fuel isn't enough. To correct this you rescale the MAF table so the ECU knows exactly how much air is entering so it can properly achieve your target AFR. You do not richen up your fuel map to do this, that would be the band aid fix.
ummm, the MAF sensor's job is to measure airflow... so if more air is flowing through the intake due to a less restrictive turbo inlet hose, guess what? the MAF will record more air. the ECU will know EXACTLY how much more air is going in. the only thing that could change this is varying MAF housing diameters and extreme turbulence.

this is clear as day to me.
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