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Old 04-18-2010, 11:36 PM   #1
Soobie22
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Default Fuel injector parameters

The Fuel Injector Scale table contains is a singular value used to tell the ECU what is the size (or flow rate) of the fuel injector it is controlling. Any
changes to this table will affect ALL tables within the ECU related to fuel delivery calculations. When using stock fuel injectors this table does not need to
be altered. When adjusting this value, a smaller scale value represents a LARGER fuel injector whereas a larger scale value represents a SMALLER fuel
injector.

To calculate a starting value for a different injector size than stock, use the following formula:
New Scale Value = (Original Injector Size / New Injector Size) * Original Scale Value.

For example, letís say you are replacing your factory WRX injectors (420cc) for aftermarket 650cc injectors. The formula would look like:
New Scale Value = (420cc / 650cc) * 6442;
New Scale Value = 4162
For another example, letís say you are replacing your factory 2004+ USDM STi injectors (500cc) for aftermarket
850cc injectors. The formula would look like:
New Scale Value = (500cc / 850cc) * 5372;
New Scale Value = 3160

I dont know if its because i am tired. But this is bothering me. Im not really sure how they got the fuel injector scale. Makes no sense to me at the moment. Since they dont really explain how they got that maybe someone on here could. Got the above from their how to guide on how to tune. Ive tuned before with dsms and didnt have to worry about that.
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Old 04-19-2010, 05:11 PM   #2
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wow, no one has an idea?
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Old 04-19-2010, 05:14 PM   #3
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WHAT?

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I don't know what you're talking about, but does this help?

http://www.rceng.com/technical.aspx?...X7SYdFzWNMw7VV
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Old 04-19-2010, 05:53 PM   #4
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its actually on cobbs site. AccessECU software calibration & training guide. Just was reading and this caught my eye and makes no sense.
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Old 04-19-2010, 06:31 PM   #5
Dutch Scooby lover
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Site seems wrong.
They divide old/new both times, but they multiply that value with a different value both times.
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Old 04-19-2010, 08:56 PM   #6
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it works. believe me.

i scaled id1000s using exactly the instructions. then i scaled them for e85 which adds even more twists..

i think if you search enough, somewhere on romraider or even here, it is explained exactly how they came up wit the number.

think of the number as telling the ecu how long to open the nozzle, the bigger the injector, the smaller the time. and the number for the bigger injectors is thusly smaller..

never-the-less. i would not have attempted tuning without a wideband.. widebands dont lie. if you get the number off, you just tweak it a bit up or down till it works..

latency is important too. but you get that from your injector provider...
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Old 04-20-2010, 06:47 AM   #7
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I know that there could be a formula for this, my PowerFC also works like this, but why do they multiply with 2 different values, that is what seems strange to me, because how/when do you use the one value (6442) and when do you use the second one (5372)
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Old 04-20-2010, 08:16 AM   #8
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just seems a lot more confusing then it actually needs to be.
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Old 04-21-2010, 10:27 AM   #9
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The fuel injector scale is the injector pulse width (IPW) for stoich fueling per gram of load (in microseconds). When the ECU is targeting a stoich "AFR", the IPW (microseconds) would be calculated load * fuel injector scale (multiply by 0.001 to get ms). This base pulse width is what the ECU uses for all fuel calculations.

The underlying value of the primary fuel map is not an AFR, but, basically, a percent enrichment over stoich. So, for example, a cell may call for 10% more fueling than stoich (13.36:1 AFR). That is applied to the base pulse width above (in open loop in this case) to determine the final IPW. All fueling calculations use the same method.

This might sound complicated, but it is actually much easier when changing injectors. Higher flow injectors will require a smaller fuel injector scale to maintain the correct stoich fueling. Since everything is based off of that base pulse width, once you change the fuel injector scale everything else will still be correct. That is, for example, a cell that targets 10% enrichment (13.36:1 AFR) will not require re-tuning if that is the AFR you wish to target with the new injectors (assuming you have the correct injector scale).

The same holds true for E85 tuning where you would increase the injector scale (all else being equal).

Remember, different manufacturers can and do use different strategies for fueling, timing, etc. There is no standard and they can sometimes be quite a bit different, even though they are ultimately calculating the same final values. This is just how Subaru does it.

Bill
Subaru ECU Discovery
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Old 04-21-2010, 10:44 AM   #10
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Quote:
Originally Posted by Dutch Scooby lover View Post
I know that there could be a formula for this, my PowerFC also works like this, but why do they multiply with 2 different values, that is what seems strange to me, because how/when do you use the one value (6442) and when do you use the second one (5372)
Those are two different examples. The first example is "factory WRX injectors (420cc) for aftermarket 650cc injectors." The second example is "factory 2004+ USDM STi injectors (500cc) for aftermarket
850cc injectors".

What you would use for your car would depend on what new injectors you are going to use and what old injectors you are replacing (presumably the OEM injectors). And then what the current injector scale is for the old injectors.

Bill
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