Adjust injector scale, or adjust MAF curve?

xlsupreme · 05-26-2010, 03:17 PM

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.

Concillian · 05-26-2010, 03:54 PM

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.

xlsupreme · 05-26-2010, 04:11 PM

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)

bswilmington · 05-26-2010, 04:49 PM

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.

Concillian · 05-26-2010, 04:55 PM

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.

dazedone · 05-26-2010, 05:14 PM

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.

NSFW · 05-27-2010, 02:26 AM

Quote:

Originally Posted by dazedone

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.

dazedone · 05-27-2010, 11:20 AM

Quote:

Originally Posted by NSFW

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

xlsupreme · 05-27-2010, 10:11 AM

the idle is pretty smooth. the car pulls well, without bucking or hesitation.

how will something combustable assist me in checking for leaks?

bswilmington · 05-27-2010, 10:32 AM

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?

xlsupreme · 05-27-2010, 11:55 AM

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.

05-26-2010, 03:17 PM	#1
xlsupreme Scooby Newbie Member#: 120789 Join Date: Jul 2006 Location: Richmond, VA Vehicle: 2005 USDM STi	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.

Thread Tools
Show Printable Version Email this Page
Display Modes
Switch to Linear Mode Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Question regarding maf and injector scaling	akeric	Open Source Reflashes	2	08-17-2009 12:35 PM
better way to reach target afrs: adjust maf scaling or fuel map?	nhat	Open Source Reflashes	37	06-16-2008 08:07 PM
WTB- Perrin BIG MAF, Perrin Inlet, STI injectors (stock or 816s+), more	BlackSTI2006	NESIC Private Classifieds	0	12-10-2006 09:49 PM
Intersting thoughts on injector scaling and resulting timing effects	Hitokiri	Engine Management & Tuning	6	06-24-2004 09:31 AM
UTEC injector scaling thoughts	cdvma	Engine Management & Tuning	19	06-05-2004 01:42 PM

05-26-2010, 03:54 PM	#2
Concillian Scooby Guru Member#: 4414 Join Date: Feb 2001 Location: Dublin, CA Vehicle: 2002 WRX Sedan Midnight Black	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.

05-26-2010, 04:11 PM	#3
xlsupreme Scooby Newbie Member#: 120789 Join Date: Jul 2006 Location: Richmond, VA Vehicle: 2005 USDM STi	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)

05-26-2010, 04:49 PM	#4
bswilmington Scooby Specialist Member#: 217563 Join Date: Jul 2009 Chapter/Region: South East Location: Eden NC Vehicle: 2006 Sti 12.68 @ 108 321WHP 422WTQ dynojet SAE	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.

05-26-2010, 04:55 PM	#5
Concillian Scooby Guru Member#: 4414 Join Date: Feb 2001 Location: Dublin, CA Vehicle: 2002 WRX Sedan Midnight Black	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.

05-26-2010, 05:14 PM	#6
dazedone Scooby Newbie Member#: 173938 Join Date: Mar 2008 Chapter/Region: NWIC Location: Oregon Vehicle: 06 sti matte black	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.

05-27-2010, 10:11 AM	#9
xlsupreme Scooby Newbie Member#: 120789 Join Date: Jul 2006 Location: Richmond, VA Vehicle: 2005 USDM STi	the idle is pretty smooth. the car pulls well, without bucking or hesitation. how will something combustable assist me in checking for leaks?

05-27-2010, 10:32 AM	#10
bswilmington Scooby Specialist Member#: 217563 Join Date: Jul 2009 Chapter/Region: South East Location: Eden NC Vehicle: 2006 Sti 12.68 @ 108 321WHP 422WTQ dynojet SAE	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?

05-27-2010, 11:55 AM	#11
xlsupreme Scooby Newbie Member#: 120789 Join Date: Jul 2006 Location: Richmond, VA Vehicle: 2005 USDM STi	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.