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Old 05-26-2010, 03:17 PM   #1
xlsupreme
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Default Adjust injector scale, or adjust MAF curve?

How do you decide which to adjust?

Let's say at WOT I'm running around 10.2:1, but I'm targeting 11.2:1. How do I decide whether I should adjust the injector scale, or adjust the MAF (V) vs. MAF (g/s) curve?

Using the stock off the shelf map from Cobb for stage 2, and I find my target values are no where effing near my actual when doing WOT pulls.

It's my thought that since the car runs mega rich in high load, but fluctuates the error in the CL phase of driving, that I need to adjust the MAF curve up top for that.
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Old 05-26-2010, 03:54 PM   #2
Concillian
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You adjust what you changed out.

If you changed the injectors, you adjust injector parameters
If you changed intake, you adjust the MAF scale.

If you changed both? You put the intake back to stock and scale the injectors with the stock MAF, then you put the new intake back and scale the MAF... or you just guess at the injectors and then scale the MAF (which is what most do, since if you get the injectors close enough, the MAF can get you the rest.)

Once the injectors are close and you have a reasonably flat MAFv curve as far as latency / flow scaling adjustment, you can use the MAF scaling to take more of the "wave' out that you can't adjust with injector parameters.
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Old 05-26-2010, 04:11 PM   #3
xlsupreme
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Well, they're both stock, but the target AFR isn't being met. like I said, I'm running silly rich (by comparison to the requested AFR)
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Old 05-26-2010, 04:49 PM   #4
bswilmington
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If your lower fuel correction below 40 g/s on sti ecu, i dont know what load columns are on wrx, are off and your higher rpms are off in same direction then i would adjust injector size to correct across board. if its off in higher rpm but close to +-5% in less than 40 g/s then i would adjust maf.

on my sti i adjusted both the injector size from 503 to 513 and rescaled part of the maf on my stock intake and my lower fuel trims were less than 4% and high rpm was almost dead on.

so the answer to your question depends on how it is off and where.
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Old 05-26-2010, 04:55 PM   #5
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In this case, I'd think the course of action is to figure out what is making you rich, not to just adjust it. It sounds like you're WAY off, not just a little off which likely means there is some other problem.

I'd look for a boost leak. A shop will be able to pressurize your intake and look for leaks. Without an adapter and an air compressor this can be difficult to do for a DIYer. Smoke machine may help, but for a boost leak, it may not show without pressure.

To start, go over all the connections in the intake tract looking for small holes and loose clamps. You can try squirting something combustible (carb cleaner) around the joints trying to find a leak, but like I said, a boost leak may not show without pressure.

Do you have a Tactrix so you can look at long term fueling trims with Learning View? This will tell more of a story.
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Old 05-26-2010, 05:14 PM   #6
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Have you made any changes that could be related to the problem?
Does your car have a rough/unstable idle ? If not its most likely not a vacuum leak

test the fuel pressure regulator http://www.2carpros.com/dia/test_fuel_pressure.htm

Look very closely at the vacuum tube going to the f.p.r. for cracks and/or leaks

Also check your pcv valve and system, up to 30% of engine intake air can passthrough the pcv system. If its clogged/restricted you will run rich.
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Old 05-27-2010, 02:26 AM   #7
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Quote:
Originally Posted by dazedone View Post
Also check your pcv valve and system, up to 30% of engine intake air can passthrough the pcv system. If its clogged/restricted you will run rich.
Why? The PCV system pulls air from the turbo inlet (downstream of the MAF sensor), and vents that air into the intake manifold (downstream of the MAF sensor). If it's clogged, you'd just have more air going through the regular intake tract (turbo, IC, etc) and less air going through the motor, but either way the amount of air entering the cylinders should be the same as the amount of air that went past the MAF sensor.
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Old 05-27-2010, 10:11 AM   #8
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the idle is pretty smooth. the car pulls well, without bucking or hesitation.

how will something combustable assist me in checking for leaks?
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Old 05-27-2010, 10:32 AM   #9
bswilmington
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you use something combustable to spray around the intake, vacuum lines, and anywhere you might expect to see a leak with the engine running. if you hit a spot with leak then engine will idle up.

do you know what your closed loop fuel trims are? if they are off it can help you determine if you have a leak.

what source of tuning are you using?
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Old 05-27-2010, 11:20 AM   #10
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Quote:
Originally Posted by NSFW View Post
Why? The PCV system pulls air from the turbo inlet (downstream of the MAF sensor), and vents that air into the intake manifold (downstream of the MAF sensor). If it's clogged, you'd just have more air going through the regular intake tract (turbo, IC, etc) and less air going through the motor, but either way the amount of air entering the cylinders should be the same as the amount of air that went past the MAF sensor.
Sorry I ment to say egr exhaust gas recalculation valve. I know stis don't have them does the wrx?

If the egr is not closing all the way, Inert gas is filling space that o2 should be filling.


xlsupreme you also need to tell us what kind of car you have,or did I miss it

Last edited by dazedone; 05-27-2010 at 11:33 AM.
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Old 05-27-2010, 11:55 AM   #11
xlsupreme
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I have an 05 STi. I'll check the joints with carb cleaner, and post a log of fuel trims in closed loop. I'm using access tuner race.
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