;
; CK RPM THRESH FOR WOT PWR ENR
;
DC06: LDAA L001C ; RPM/25
DC08: CMPA LD2D0 ; 2000 RPM THRESH FOR PWR ENRICH
DC0B: BCC LDC13 ; BR IF RPM GT 2000 RPM
; ... else
DC0D: SUBB LD2D1 ; 1.5:1 AFR PWR ENRICH FOR COLD
DC10: BCC LDC13 ; BR IF GT 1.5:1
; ... else
DC12: CLRB
DC13: LDC13: LDAA L00A5 ; OPN LP AFR
DC15: CBA ;
DC16: BLS LDC2F
; ... else
DC18: STAB L00A5 ; OPN LP AFR
DC1A: LDC1A BRA LDC2F ;
;-------------------------------------

Ok I was looking through the 747 hack because it doesn't seem like adjusting the PE AFR table does much to change my WOT PW times. Although the upper VE does. This snippet from the 747 hack is one of the qualifiers that has to happen before PE is enabled. The Line

BR IF RPM GT 2000 RPM

leads me to believe that PE won't happen unless your UNDER 2000 rpm. I read this line as " break if RPM is greater than 2000 RPM" Is this correct? And if so where is my motor getting the extra fuel it needs at WOT? I just need a reality check.

 

Looking at that snippet there at a quick look at the hac, it looks like PE happens, but that 1.5 AFR bias isnt subtracted out from the AFR in accumulator B. The CBA makes sure that the PE afr isnt numerically greater then the open loop AFR. It saves the lower of the two as the commanded AFR and moves on.

 

that makes sense now that I go back and look at all the code for PE. I just saw that one little section and and it rang a bell.

Does anyone know the math routine that the ecm goes through to calculate PE AFR from your base VE? I'm kinda wanting to visualize how much VE % corresponds to to actual AFR or at least calculated AFR.

 

Well, the actual AFR will depend on how closely the tables and everything in the ecm coorespond to the motor itself. As you know the fuel calculations are only indirect estimates since the actual airflow isnt known.

The math (in people friendly terms) is something like this: The fueling in the ecm is done on a single cylinder basis since one injector fires each time a cylinder fires. The ecm uses the manifold pressure, volumetric efficiency, the air density and various corrections in some form, and the cylinder volume in the BPW constant to basically construct an estimate of the mass of air in the cylinder. The VE gives a ratio of the volume of air taken in to the total cylinder volume. The MAP, correction factors, and some form of air density relates the mass to the volume of air in the cylinder. The air fuel ratio is used to relate the mass of fuel needed for the given mass of air. Finally the injectors flowrate in the BPW constant provides a pulsewidth, or time for the injector to be open. Since the injectors flowrate is mass of fuel flowed per unit time, dividing the mass of fuel needed by the mass of fuel that can be flowed with time, an actual time that the injector needs to be on is the result.

There is also lots of other corrections to go along with this but that pretty much gives teh core pulsewidth.

The actual code looks pretty funky and is sort of an approximation to SD, which is probably due to the fact that tbi is a wetflow system, but from what I can tell thats thats sort of what the code does.

 

I think thats right anyway. Its all so complicated

 

Thanks, Demented. Thats kinda what I figured. I'm still digging through the math section of the code trying to find exactly where it's done. I'd like to come up with a fast and DIRTY way of relating x amount of VE is worth X amount of AFR. Just for visulization purposes. Of course this will be different for every engine, depending on BPW constants and such.

 

The VE and the AFR are really two seperate things that are used in calculating the BPW. I guess you could use a general form of the equation used for calculating the BPW and then get the VE in terms of everything else, but it wouldnt be a quick and dirty way to relate them to eachother. Youd have to know all the other variables like the map value and temperature correction when you calculate it out.