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Old 08-10-2009, 07:05 PM   #1
Scooby Specialist
Member#: 122954
Join Date: Aug 2006
Chapter/Region: AKIC
Location: Anchorage, AK
2006 Evo IX
My car is black not

Default Question regarding maf and injector scaling

I did use the search function and apparently injector scaling and maf scaling are 'too common'.... so I looked back about 20 pages but still didn't find the answers I was looking for. I did read however that its best to only changes injectors, scale those and then the maf.... or vice versa.

So I'm just finishing up my turbo setup on my 07 Sti....went with a Borg Warner S256 turbo... did a custom up-pipe, down-pipe, TGV port delete and coating... stock manifold port and coating, new GrimmSpeed BCS, and FIC 850cc injectors and a Cobb 72mm Big MAF.

So now that everything is coming back together I need to scale the new injectors and the new MAF I no longer have the stock injectors. I have the flow sheet from FIC that lists the max flow in cc/min for all the injectors 3 rate at 862 and one at 866 at 44psi fuel pressure. It also lists all of my latencies for a given battery voltage.

Are these values from the builder good enough to use? For example the battery voltages listed on the flow sheet do not match the exact values already in the latency map. Do I need to just replace all the values or is it better to keep the stock voltages references and extrapolate the proper latency values?

Now I do have the stock intake track but I am building a 3" intake and there is no way the stock one will fit there without using say ductape to hold it together. Would you seriously recommend using the stock maf sensor ductaped into to the intake and use that to calibrate the injectors? Is this seriously foolish? is there a better way? not that I have a problem using ductape....... anyway let me know

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Old 08-11-2009, 01:12 AM   #2
Scooby Specialist
Member#: 156973
Join Date: Aug 2007
Chapter/Region: International
Location: Adelaide, Australia
2002 ADM WRX STi
STi Black/Blue


Put stock intake, airbox and maf housing back on, then sort out your injector latencies and injector flow scaling. Once injectors are set, reinstall your aftermarket intake, MAF housing and rescale your MAF.

There are utilities available on the RomRaider forum that will help you sort out your injectors and scale your MAF.

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Old 08-17-2009, 01:35 PM   #3
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Member#: 14911
Join Date: Feb 2002
Chapter/Region: MWSOC
Location: The land of E85
Not A Wagon!
2011 WRX - 285s on 18x9.5


I'm still unsure why everyone whines and moans about how tough it is to scale MAF and injectors at the same time. I can usually do it in less than 2 hours. The most important step is to make sure there are no vacuum leaks. You can use formulas to get a starting value for the MAF (This formula is for increased MAF diameter):

Injector size / (New MAF diameter / Old MAF diameter)

Plug that value in as the injector scaler and then start the car and let it warm up for 10 minutes. I always leave the hood open so heat doesn't build up in the intake. Now log AF Learning and AF Correction with the engine idling for a few minutes. Open the log and add the values together (easy in excel) to create a new column called AF Total. Average the AF Total column. If the average is positive, increase the Latency by small amounts until the average is close to -2.

Now you can do some cruise logging (with the engine still warm). Try to hold steady throttle and speed for at least a few minutes at various RPMs and gears from 1500 - 4500 rpm in 300-500 rpm increments while logging. I use my own spreadsheet to average out the values at the different MAF volt points in the MAF table, but you could use RomRaider or one of the downloadable spreadsheets. The basic idea is that you need to adjust the latency so that the corrections are the same value accross the whole MAF table. Then adjust the scaler so the correction is close to 0 across the whole MAF table. Learning View is a great tool here and here are some examples of what you may see:

  A	   	   B	  	  C	 	 D
0-5.6		5.6-10		10-50		50+
15.00		10.00		7.00		5.00
Increase the latency

  A	   	   B	  	  C	 	 D
0-5.6		5.6-10		10-50		50+
-2.00		-7.00		-11.00		-15.00
Decrease the latency

  A	   	   B	  	  C	 	 D
0-5.6		5.6-10		10-50		50+
-2.00		5.00		10.00		15.00
Increase the latency
After increasing or decreasing the latency correctly, you should see something like this:

  A	   	   B	  	  C	 	 D
0-5.6		5.6-10		10-50		50+
0.00		1.00		3.00		2.00
Current scaler / 1.02

  A	   	   B	  	  C	 	 D
0-5.6		5.6-10		10-50		50+
-17.00		-14.00		-13.00		-15.00
Current scaler * 1.15

  A	   	   B	  	  C	 	 D
0-5.6		5.6-10		10-50		50+
16.00		17.00		19.00		18.00
Current Scaler / 1.18
Of course you can't always get that lucky and you may see something where the MAF needs tuned like this:
  A	   	   B	  	  C	 	 D
0-5.6		5.6-10		10-50		50+
-2.00		-7.00		1.00		0.25
Tune the MAF values in the B range
Now that you've dialed in the Closed loop, you can hook up your wideband and tune open loop. I like to start at low boost (1-5 psi) and do a few runs then check the log. Adjust the table by 1% for every 0.1 AFR off from the target for each of the MAF table columns. Then increase the boost a few psi and log again and adjust.

If you notice a trend in the open loop such as you're adding 8-10% accross the entire MAF table, you may want to change the scaler by 9% and then retune the closed loop. If you notice that higher MAF volts is requiring steadily increasing corrections (positive or negative), you may want to change the latency and retune the closed loop. I wouldn't bother retuning the closed loop for less than 6% correction in the open loop values.

Remember, increasing the injector scaler decreases the fueling and increasing the MAF values increases the fueling.
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