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Old Thu, Aug-18-2016, 03:24:36 PM   #1
SliM3
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Default Global Fuel Factor: Definitive & Final Guide to Calbrating MSS54 for Larger Injectors

Greetings all:

I have made quite a bit of posts in the past in regards to using the global fuel factor (K_TI_GA) to accommodate larger injectors, or to increase flow rate of stock injectors for use of 50/50 mix 93 & E85. Though I was working with this scalar on a very limited basis, and making minor adjustments to accommodate very small flow rate changes, it wasn't until working with my large injectors that I realized exactly how this adjustment is calculated in the background.

I will try to explain it in this thread, but please be forewarned, I'm not a binary guru so for the guys that are, please excuse my terminology if it is not the industry standard. Please correct me as well, as that arms me with more "key words" to search-out and learn about.

So just to recap the operation of the global fuel factor; It is a multiplicative scalar that is calculated after all other fueling factors have been determined, and affects the final injector pulse width (PW). This is an across the board change, so by making changes to the factor you are adjusting everything from starting PW, after-start PW, to warm-up PW, to idle, to cruise, to WOT

Now here's where all the binary math gets to be a little crazy! Well, at least I had to change my mindset when working with binary math. Probably nothing new to the experts. LOL
As mentioned, the multiplicative global factor is neutral at "1". If we were to add fuel, say 1.25, the binary math operation (multiplying) remains the same, and you pretty much increase fuel flow linearly.
Now, when we take fuel away we have to input a decimal, and this where the binary math changes. Because binary doesn't work with fractional numbers (decimals), it has to make sign changes in order to calculate; i.e. changing the operand from a positive number to a negative number.
So in essence if you want to take 40% out of the injector PW, you would think setting the factor to 0.60 would be the target you're after (1 - 40% = 0.60). Big hand on big buzzer button. WROOOOOONNNGGG!!

What we need to do is calculate fuel mass flow rates for the stock injectors and your new injectors, using some information that's already available to us in the DME. Let's start:

F U E L I N J E C T O R M A S S F L O W R A T E S
The stock injectors flow 257cc/min (Information provided by MEPEH Injectors). We need to convert this to mass flow rate, down to the mg per msec. Then we must account for the increased flow rate due to 5-bar fuel pressure. I use Witch Hunter Fuel Injector Calcs..





Our stock injectors have a final fuel mass flow rate of 31.6 lbs/hr. We need to break this down to mg/msecs. For this, I just use the conversion and calculator apps on my phone.
  • 31.6 lbs/hr = 14,333,519 mg/hr
  • 14,333,519 / 60 minutes = 238,892 mg/min
  • 238,892 / 60,000 msecs = 4 mg/msec

Let's use my 1100cc injectors:
  • 135.3 lbs.hr = 61,371,048 mg/hr
  • 61,371,048 / 60 minutes = 1,022,850 mg/min
  • 1,022,850 / 60,000 msecs = 17 mg/msec


Now that we have our flow rates, we need to figure out what the fuel requirements are for the engine, based on what's commanded by the DME. The best way to determine this is to use the start factor (K_TI_START). Even though this is actually your "raw" cranking PW, when the global factor is set to "1", it still gives us an idea of what the fuel flow requirements should be.

F U E L M A S S F L O W R A T E R E Q U I R E M E N T
  • 9.7 msecs * 4mg/msec
  • Cranking fuel mass flow = 39 mg


Now that we have the fuel requirement, we can figure out the equivalent PW requirement for our new larger injectors.
  • 39 mg / new injector flow rate
  • 39 / 17 = 2.3 msec PW for 1100cc injectors


Remember how I said the binary math changes when dealing with decimals?? Follow along:

We take our new PW of 2.3 msec and divide that by the start factor 9.7. That will give us a percentage of reduction, so to speak.
  • 2.3 / 9.7 = 0.24

Naturally, you would think 0.24 is your final global factor! But again, that crazy math requires us to make the "sign" change to find THE REAL value to set.
  • 0.24 - 1 = -0.76


Since the sign change happens behind the scenes in the DME program, your final factor for running 1100cc injectors will actually be 0.76 K_TI_GA, w/out the negative.

To back check your math, convert the global factor to a percentage (0.76*100 = 76%). Now take that percentage and subtract it from the start factor.
  • 9.7 - 76% = 2.3 msec cranking PW

Keep in mind that your new global factor will be applied to pretty much all factors controlling fuel injection. So in essence if you're just dropping in larger injectors with no other changes, you should see the same AFR's as stock, and you'll alleviate the need to address individual maps to make the injectors work.

Of course you can fine tune by setting your cruise map to "1" (14.7), setting all the additional factors to "1" so they don't make any corrections, and datalog AFR's. If you over or undershoot your target just make your little adjustments, and bam, you're injectors are now calibrated to your DME.

If you're looking to run 100% E85, just add anywhere from +35% to +42% to the fuel mass flow requirement (39 mg), and do your calculations from that; i.e 39 + 42% = 55 mg
  • 55 mg / 17 mg-msecs = 3.2 msec requirement for E85
  • (3.2 / 9.7) - 1 = 0.67 K_TI_GA


I hope this explains it somewhat clearly.
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- Checksum corrections for modified DME partial & full bin files

- CSL SMG Engine Parameters (DME) by Slim

- Fuel adaptations explained

- Checksum Verification

Last edited by SliM3; Thu, Aug-18-2016 at 03:34:10 PM.
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Old Wed, Aug-24-2016, 01:54:00 PM   #2
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Default Re: Global Fuel Factor: Definitive & Final Guide to Calbrating MSS54 for Larger Injec

Quote:
Originally Posted by SliM3 View Post

I hope this explains it somewhat clearly.
Brilliant as always
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Old Sat, Aug-27-2016, 12:52:32 AM   #3
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Default Re: Global Fuel Factor: Definitive & Final Guide to Calbrating MSS54 for Larger Injec

Is there an editable table for injector response time/offset? Should be vs. system voltage at the very least. The above should work to rescale injector pulse for medium and full load, but likely the idle and light throttle fueling will be off due to different injector response time.
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Old Sat, Aug-27-2016, 04:28:10 AM   #4
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Default Re: Global Fuel Factor: Definitive & Final Guide to Calbrating MSS54 for Larger Injec

BBR:
There is, but you have to disable idle sync for the parameters to take effect.

As far as changing idle AFR's, there is a simple scalar that does just that. However, the global factor will pull the idle PW's down as well. Too low IMHO!! I'll post that scalar when I get back to the grind in a week.


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- Checksum corrections for modified DME partial & full bin files

- CSL SMG Engine Parameters (DME) by Slim

- Fuel adaptations explained

- Checksum Verification
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Old Fri, Jul-07-2017, 09:58:27 PM   #5
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Default Re: Global Fuel Factor: Definitive & Final Guide to Calbrating MSS54 for Larger Injec

Hey Brian,

I hope you're well!

I've just been running through the calcs above but I can't seem to make them work.

Here are my workings:

Injector Specs:

38.1 lb/hr / 288031.15 mg/min / 4.8 mg/msec

Fuel Requirement

39 / 4.8 = 8.125 msecs

New PW / Start factor (9.7)

8.125 / 9.7 = 0.838

Signed Value

0.838 - 1 = -0.162

Now doesnt a K_TI_GA value of 0.16 seems a little on the low side or have I missed something obvious?
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Old Sat, May-04-2019, 06:48:12 PM   #6
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Default Re: Global Fuel Factor: Definitive & Final Guide to Calbrating MSS54 for Larger Injec

Hello slim3 I do not understand how your factor for E85 is smaller than your factor with SP93

You say K_TI_GA 0.76 for SP93
and 0.67 for E85 it is not correct.

when K_TI_GA is smaller the car becomes leaner.

and for E85 you need more fuel

with your calculation and my injectors 850cc for 43.5psi
I get everything to fix K_TI_GA 0.70 so this figure is smaller than yours when it should be bigger.

I work a lot on Bosch ME3.8.3 VAG 1.8Turbo and for find factor I just use cross product the original factor is 1 also.

for example
original injector 260cc
new injector 630cc

I do 260 / 630 x 1 = 0.412 I just add 35% to 0.412 for E85 then I disable O2 regulation and I start my adjustment with this base. it's very simple and i get very good result in this way.

I do not understand exactly how you do it.
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Old Sun, May-05-2019, 02:04:15 PM   #7
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Default Re: Global Fuel Factor: Definitive & Final Guide to Calbrating MSS54 for Larger Injec

You are missing a big chunk of what he's saying.

Slim does a really good job on most of the explanation but I think he has a slight terminology glitch:

Quote:
Originally Posted by SliM3 View Post
We take our new PW of 2.3 msec and divide that by the start factor 9.7. That will give us a percentage of reduction, so to speak.
  • 2.3 / 9.7 = 0.24

Naturally, you would think 0.24 is your final global factor! But again, that crazy math requires us to make the "sign" change to find THE REAL value to set.
  • 0.24 - 1 = -0.76
So I think his lingo is a bit confusing.

Actually the 24% isn't the 'reduction'.
Its the actual magnitude of the new pulse compared to the original.

Aka: "the new injectors only need 24% of the pulse that the old ones did".

Doing the additional calculation to get the inverse - 76% ...
Now that DOES give you the reduction.

Aka: "reduce the specified pulse by 76% for these injectors" is what that means.

And since the value is for a reduction, then a smaller value = more mass and a larger value = less mass, which is why he shows a smaller 'reduction' value for E.

I can't comment on if this is the best way to accomplish injector scaling or if there's not some other problem but assuming Slim has it right, that's what he is trying to say, and maybe that helps clarify.
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Old Sun, May-05-2019, 03:01:04 PM   #8
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Default Re: Global Fuel Factor: Definitive & Final Guide to Calbrating MSS54 for Larger Injec

IIRC there is a parameter called qstat, which should be injector static flow rate. I haven't tried it myself but I believe you should be able to adjust qstat rather than changing the global fuel multiplier. That multiplier is probably there as a development tool and was not really intended to be used in the final cal.

I've brought this up before and posted in more detail but got no response. If someone has interest in this I can try to dig up my old post.
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Old Sun, May-05-2019, 03:24:51 PM   #9
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Default Re: Global Fuel Factor: Definitive & Final Guide to Calbrating MSS54 for Larger Injec

Cool. I was wondering about that. But its always tricky until somebody has really tested a parameter though - BMW/Bosch/Siemens/everybody will often leave junk lying around that can be 'unused' in various programs. Ideally somebody running big injector E setup confirms that they are using that approach and that is the way to go...

The other point that is important to re-state is that the latency tables should be updated with any injector changes.
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Old Sun, May-05-2019, 07:22:29 PM   #10
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Default Re: Global Fuel Factor: Definitive & Final Guide to Calbrating MSS54 for Larger Injec

Quote:
Originally Posted by ctres View Post
IIRC there is a parameter called qstat, which should be injector static flow rate. I haven't tried it myself but I believe you should be able to adjust qstat rather than changing the global fuel multiplier. That multiplier is probably there as a development tool and was not really intended to be used in the final cal.

I've brought this up before and posted in more detail but got no response. If someone has interest in this I can try to dig up my old post.
I want to say that's one of the parameters that appears in the funktionsrahmen, but not found in the production code.
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