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determine engine load with MAP or MAF?? 
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hello guys. i am trying to figure out, how you determine the engine load....
1)the fuel that needs to be injected, is depended only on the Engine load?? (assuming you target stoichometric). if it is depended on RPM as well, then why?

2) i get that the MAP Sensor, measures the vacuum of the manifold, and the MAF, measures the incoming air, But which one, gives the actual engine load??


Mon Jan 27, 2014 2:50 pm
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QFP80 - Contributor

Joined: Tue Feb 12, 2013 5:43 am
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Location: Scarborough, ON
1. The fuel is injected according to the engine load and the desired AFR. Where it gets interesting is that the engine load (and power available) varies with RPM due to the breathing ability and resonant effects. A 20% throttle opening at 4000 rpm will likely require a significantly different amount of fuel than the same throttle opening at 8000 rpm, even though the throttle position is the same.

2. Either can be used to determine engine load. MAP is typically less accurate, as the MAP timing window must be carefully selected to consider resonant fill effects, the IAT sensor must be properly calibrated (and is subject to heat soak - lean hot restart issues is a common complaint with MS), and other problems. MAF is typically far more accurate and easier to use - enter the transfer function into the firmware, and let it do its thing. If you don't know the transfer function, or you're adapting a MAF sensor from a different vehicle, then calibrating the MAF sensor can be quite difficult, to the point where it's simply easier to use a set of MAP and IAT sensors.

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Mon Jan 27, 2014 8:09 pm
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DonTZ125 wrote:
1. A 20% throttle opening at 4000 rpm will likely require a significantly different amount of fuel than the same throttle opening at 8000 rpm, even though the throttle position is the same.


yes, but isin't this reflected to the outpout of the MAF sensor?? i mean, at 20% throttle, and 4000rpm, the MAF outpout will be less than 20% throttle and 2000rpm ???

DonTZ125 wrote:
2.. MAF is typically far more accurate and easier to use - enter the transfer function into the firmware, and let it do its thing. If you don't know the transfer function, or you're adapting a MAF sensor from a different vehicle, then calibrating the MAF sensor can be quite difficult, to the point where it's simply easier to use a set of MAP and IAT sensors.


i want to use MAF, because it seems way more easier to implement, both mechanically, and in software.. but all the hardware (electronics), and software i will be using, are going to be made by me.
so, do i really need a transfer function??my plan so far was to :

determine the lower and max MAF values.
then make a table with 10 - 20 or whatever, MAF values
and then , fine tuen the best fuel needed for each, with the help of a wideband..

(if something of the above seems stupid, please adress them seperatly, so i can understand :P :P )


Mon Jan 27, 2014 8:20 pm
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QFP80 - Contributor

Joined: Tue Feb 12, 2013 5:43 am
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Location: Scarborough, ON
settra wrote:
DonTZ125 wrote:
1. A 20% throttle opening at 4000 rpm will likely require a significantly different amount of fuel than the same throttle opening at 8000 rpm, even though the throttle position is the same.


yes, but isin't this reflected to the outpout of the MAF sensor?? i mean, at 20% throttle, and 4000rpm, the MAF outpout will be less than 20% throttle and 2000rpm ???

The MAF sensor doesn't care what the rpm is, it reports what the air flow IS. 20% at 2k could be more that 20% at 4k, it could be less. Depends on the engine. Mine hits max power at 16500 rpm; yours is probably flowing zero air because the pistons went through the head.

Quote:
DonTZ125 wrote:
2.. MAF is typically far more accurate and easier to use - enter the transfer function into the firmware, and let it do its thing. If you don't know the transfer function, or you're adapting a MAF sensor from a different vehicle, then calibrating the MAF sensor can be quite difficult, to the point where it's simply easier to use a set of MAP and IAT sensors.


i want to use MAF, because it seems way more easier to implement, both mechanically, and in software.. but all the hardware (electronics), and software i will be using, are going to be made by me.
so, do i really need a transfer function??my plan so far was to :

determine the lower and max MAF values.
then make a table with 10 - 20 or whatever, MAF values
and then , fine tuen the best fuel needed for each, with the help of a wideband..

(if something of the above seems stupid, please adress them seperatly, so i can understand :P :P )

What you're describing is a VE table, and is how you tune in a MAP system. Now, you can ALSO datalog the MAF output, and correlate MAP / VE values to MAF values, but it takes a long time.

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Mon Jan 27, 2014 8:29 pm
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DonTZ125 wrote:
The MAF sensor doesn't care what the rpm is, it reports what the air flow IS. 20% at 2k could be more that 20% at 4k, it could be less. Depends on the engine.

hm?? can the engine drow more air, that what it needs?? where does it go then ? :P


DonTZ125 wrote:
What you're describing is a VE table, and is how you tune in a MAP system. Now, you can ALSO datalog the MAF output, and correlate MAP / VE values to MAF values, but it takes a long time.


so , in order to do that, i would need a MAP sensor? not a MAF? i have them comfused it seems... do you have a good source, to help me understand this?


( my problem is, that since i begin from scratch, i will not have the slightest basic table to begin with...
i suppose i could make a 3d table, with MAFoutpout/RPM/fuel needed, but in order to do that, i would need to go to a DYNO??
i was hoping the tuning could be on my garage, with neutral... :/ )


Mon Jan 27, 2014 8:36 pm
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QFP80 - Contributor

Joined: Tue Feb 12, 2013 5:43 am
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Location: Scarborough, ON
The engine always draws in as much air as it can, taking into account port size, runner size and shape, carb / TB size, etc etc etc. The engine may draw more air at 2k vs 4k; it may draw less. Depends on the engine. The MAF will sense how much air is flowing (or calculate it from the MAP and IAT sensors according to the VE table), and the ECU will inject the appropriate amount of fuel according to the AFR table.

MAF sensor - again, if you know the transfer function of your sensor, plug it into the firmware and you're done. If you don't, you have a long and laborious struggle ahead of you.

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Mon Jan 27, 2014 8:48 pm
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ok cool. worst case senario, i will get a maf sensor with known transfer function :)


Mon Jan 27, 2014 8:50 pm
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after all, what kind of table , should i produce ??

engine load - fuel needed ??
engine load - rpm - fuel needed ??


Mon Jan 27, 2014 9:15 pm
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settra, a few words of advice: try something and see, try something else and see, this is how russian learned enough to get his engine barely running. It'll serve you well too. Asking for answers on a plate will not help you in the long or even medium or EVEN short terms. Learning will help you. Learning first hand will help you most.

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Mon Jan 27, 2014 10:36 pm
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believe me, i know :) i will anyway , have to do it trial and error way :)
i just look to find any info i can, before my exams are over, when i will start , to actually do things..
the project will anyway be hard, so why not take as much advice as you can... :)


Mon Jan 27, 2014 10:43 pm
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