Rbob, One more calculation question-MAF BPW
09-14-2004, 12:40 PM
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Rbob, One more calculation question-MAF BPW
Rbob, man, I'm a pain, sorry 'bout that........but...
so I've gotten some help from you to describe the MAF calculations(courtesy of older posts), and just recently you broke down the LV8 calculations, but I'm kinda stuck on the last deal of how the ecm generates the final base pulse width.
I have some formulas, both from previous threads, and the couple of hac's, what the real answer, how does the math work?
bpinj/5=89*inj bc*lv8/(1024*LV scalar)
thats listed in one of the hacs in the comments.
?bpw=airflow*drp
this I saw in some older posts, but that can't be the full equation.
the ecm also calcuated the 14.7:1 afr to a number around 446 or something like that......dividing 65536 by the ratio
so how does it all tie together?
thanks!
so I've gotten some help from you to describe the MAF calculations(courtesy of older posts), and just recently you broke down the LV8 calculations, but I'm kinda stuck on the last deal of how the ecm generates the final base pulse width.
I have some formulas, both from previous threads, and the couple of hac's, what the real answer, how does the math work?
bpinj/5=89*inj bc*lv8/(1024*LV scalar)
thats listed in one of the hacs in the comments.
?bpw=airflow*drp
this I saw in some older posts, but that can't be the full equation.
the ecm also calcuated the 14.7:1 afr to a number around 446 or something like that......dividing 65536 by the ratio
so how does it all tie together?
thanks!
09-16-2004, 09:45 AM
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I've been doing some more digging, and found a quote from Rbob that describes the formula:
'quote'
The PW calculation in the $6E code is even more straightforward. They take the airflow and multiply it by the inverse RPM. This converts a steady air flow rate to a pulsed rate by frequency. The commanded AFR is factored in followed by the injector flow constant. Add/subtract the blm/int/proportional terms and out pops a PW.
so that pretty much gives you:
BPW=gms/sec airflow/RPM*(AFR)*Injector flow*BLM correction
my question(s) is for the actual values used.
the gms/sec airflow= actual gms/sec determined from look up? (eg. 20g/s)
inverse RPM, ex. 1/6000 rpm, or DRP (@ 6000, 164)?
AFR, the value of 445 as coded?
finally, injector flow rate, single fire or double fire, (value of 441 or 882)??
thanks for any info!!
Joe
'quote'
The PW calculation in the $6E code is even more straightforward. They take the airflow and multiply it by the inverse RPM. This converts a steady air flow rate to a pulsed rate by frequency. The commanded AFR is factored in followed by the injector flow constant. Add/subtract the blm/int/proportional terms and out pops a PW.
so that pretty much gives you:
BPW=gms/sec airflow/RPM*(AFR)*Injector flow*BLM correction
my question(s) is for the actual values used.
the gms/sec airflow= actual gms/sec determined from look up? (eg. 20g/s)
inverse RPM, ex. 1/6000 rpm, or DRP (@ 6000, 164)?
AFR, the value of 445 as coded?
finally, injector flow rate, single fire or double fire, (value of 441 or 882)??
thanks for any info!!
Joe
09-16-2004, 05:53 PM
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Car: check
Engine: check
Transmission: check
This looks correct:
To convert from RPM to DRP for an 8 cylinder:
983040 / RPM = DRP
The inverse of this is what the ECM uses to convert the number of counts between DRP pulses to RPM:
983040 / DRP = RPM
The constant 983040 varies according to the number of cylinders.
The AFR term of 445 is for 14.7:1. This will change with the commanded AFR (such as PE mode).
The double fire term of 441 will change to 882 if in single fire mode. Double fire is an injector firing every revolution, single fire is an injector fire every two revolutions.
The term itself is the injector flow term.
RBob.
Code:
; ; calc PW ; ; PW = (((((DRP * gms/sec) / 512) * AFR) / 256) * InjFlwRate / 128) * 0.01526 ; ; 4,000 RPM, 128 gms/sec., 445 AFR, 441 secs/gms Inj: ; ; PW = ((((((246 * 128) / 512) * 445) / 256) * 441) / 128) * 0.01526 ; ; = 5.62 msec. ;
983040 / RPM = DRP
The inverse of this is what the ECM uses to convert the number of counts between DRP pulses to RPM:
983040 / DRP = RPM
The constant 983040 varies according to the number of cylinders.
The AFR term of 445 is for 14.7:1. This will change with the commanded AFR (such as PE mode).
The double fire term of 441 will change to 882 if in single fire mode. Double fire is an injector firing every revolution, single fire is an injector fire every two revolutions.
The term itself is the injector flow term.
RBob.
09-16-2004, 07:40 PM
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thats awesome, thanks!!
I was having real trouble trying to figure out the variables and there seems to be alot more to the calcualtions to convert the numbers than I thought, so that really clarifies.
its hard to convert the assembly back to an easily understood equation for me.
you da man!
I was having real trouble trying to figure out the variables and there seems to be alot more to the calcualtions to convert the numbers than I thought, so that really clarifies.
its hard to convert the assembly back to an easily understood equation for me.
you da man!
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