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Old 08-24-2009, 11:11 AM   #1
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Default Req fuel "supposedly" tuned

I used to have a 93 MSPNP and the req fuel started at 14 and went to around 7 after i upgraded to 460 cc injectors

I never had any issue with that car, however I'm currently running a 97 with MSPNP but have nothing but problems with it

If I remember reading correctly, when using the req fuel calc the AF ratio is supposed to be 12? either way if its 12 or 14.7, the req fuel would go down to a lower number

The car was "tuned" by a local shop that supposedly does MS, however now my req fuel is at 16.5
this is causing my fuel map to really suck, the lowest value is 15 and the highest is 45, so i have roughly only 30 points between highest and lowest VE

the car is running ok for now, however I know there has got to be a way to set this thing up so i have a much wider range of VE, right now if I go up or down a point I'm either running way to rich or far too lean

this is high res code but I'm not getting the benefits of it the way its set up now. the older car ran the standard code

does anyone have a sample map of what a 1.8 with 460cc injectors should be? something i can start off roughly?
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Old 08-24-2009, 11:14 AM   #2
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turn off baro.

req_fuel number doesnt really matter so long as the vetable is scaled correctly.
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Old 08-24-2009, 11:38 AM   #3
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Quote:
Originally Posted by Braineack View Post
req_fuel number doesnt really matter so long as the vetable is scaled correctly.
+1.

My Req_Fuel number, for instance, is complete fiction. I chose a value of 3.5, based solely on the mathematical coincidence that this causes every increment of 1 on the VE table to be an even multiple of the system's native PW resolution.

Just tune the VE table for target AFR, and don't worry about the actual numbers.
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Old 08-24-2009, 11:58 AM   #4
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A req fuel that is not 'correct' will result in an incorrectly reported injector DC though won't it?
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Old 08-24-2009, 12:20 PM   #5
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Nope.

Req_Fuel is just a constant that gets multiplied against VE (which is a percentage) to produce a duration. For the purpose of this example, I'm going to ignore MAP, baro, gammaE, lag, etc., and just look at one small part of the code.

Let's say that Req_Fuel is 10, and you're in a cell that has a VE of 50. 50% of 10ms is 5ms, so the commanded injector duration is 5ms.

Duty cycle gets measured after this calculation is done, as a function of RPM, and is not used in any way by the actual fuel delivery mechanism, it's just reported so you can log it. Let's say that you're at 6,000 RPM, which is 100 RPS, or 10 milliseconds per revolution, or 20 milliseconds per cycle. An injector duration of 5 milliseconds, and a cycle time of 20 milliseconds, means that injector DC is 25%. This, incidentally, is why it's possible for DC to be more than 100%. If the commanded duration that results from the Req_Fuel/VE calculation is more than the available cycle time, the injector will of course simply go to 100% DC (fully on), however the math for DC% still gets done as though the commanded duration were not impossible to achieve.


Now, let's say that without changing the injectors we cut Req_Fuel in half, to 5ms. At the same time, we multiply the whole VE table by 2. So now, under the same conditions as above, we have a VE value of 100. So, 100% of 5ms is 5ms, so just as before, the commanded duration is 5ms, and assuming the RPM to still be 6,000, calculated duty cycle is still 25%.
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Old 08-24-2009, 01:18 PM   #6
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It sounds to me like you scored a shitty tune more than anything else. Post a pic of the log and we'll let you know.
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Old 08-24-2009, 04:05 PM   #7
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Quote:
Originally Posted by richyvrlimited View Post
A req fuel that is not 'correct' will result in an incorrectly reported injector DC though won't it?
No, Required Fuel is merely the base pulse width. Take Required Fuel, multiply it by the VE percentage, scale it by the air density correction factors to get the real pulse width when there are no other enrichments applied.
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