Synch vs Asynch fueling

[RobertISaar]

the IDC calc being correct depends on if whoever wrote the ADX accounted for the injector firing pattern. my cars are all double-fire MPFI and SFI and their ADXs are setup as such.

[EagleMark]

chevmasta had quoted he found it on FullSizeChevy and I had found it as well, from 2007 IIRC. It was wrong then and it's wrong now for TBI...

[EagleMark]

Back to Async... From what this disassembly says it was never based on time without DRP... the 12.5 is the MAX Async BPW. 80 was divided by firings all based of DRP converted to Duty Cycle.

 ;~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
; Here to enter asnyc fire, convert sync BPW to async firing time
;~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
;											
L8507	CLRA				;
	CLRB				;Clear out sync BPW
	STD     L3FCE			;TBI injector driver hardware
	JSR     LF08A			;Short delay
;
;-Convert BPW to a duty cycle
;
	LDD     L3FC0			;DRP
	ASLD				;x2 for quad injector firings
	BCC     L8518			;Bra if no overflow
;											
	LDD     #$FFFF			;Clear overflow
;
L8518	XGDX				;Swap result into X    
	LDD     L0271			;Sync BPW
	FDIV				;BPW/DRP x 65536, now %DC 
;
;-%DC x (1/80 firings), or 12.5 msec per asnyc firing

[damanx]

What is Asych and Synch operation?

[EagleMark]

Asynchronous fueling is both injectors firing each DRP (Distributor Reference Pulse)

Synchronous fueling is alternating injector firing each DRP (Distributor Reference Pulse)

http://www.gearhead-efi.com/Fuel-Inj...Asynch-fueling

[damanx]

Ok, that explains why when I was playing with a dso program on my laptop and looking at the injector pulses, they went from alternating to simultaneous, as in this video I made.

Also, is the 1227747 ecm a 2k pulse per mile or 4k? EDIT: looks like 2k per mile.

[gregs78cam]

Asynchronous fueling is both injectors firing each DRP (Distributor Reference Pulse)

Synchronous fueling is alternating injector firing each DRP (Distributor Reference Pulse)

http://www.gearhead-efi.com/Fuel-Inj...Asynch-fueling

I am pretty sure that Asynch Fueling is pulsing the injectors at 80Hz regardless of DRP. That is why you can't have more than 12.5ms injector pulsewidth, because that is 1/80th of 1 second.

[EagleMark]

Yeah, I know, but it still does not make sense... then I found some algorithm that says it uses BPW/DRP to convert to duty cycle before it goes Async. Last post of this thread:
http://www.gearhead-efi.com/Fuel-Inj...-fueling/page6

Sure killed a good thread, no comments so I'm not sure. More I learn about hacks and comments the more I'm sure nothing is guaranteed accurate. Scope patterns in that thread seemed to show Sync to Async firings still at DRP?

One thing I haven't found anyone argue is Async sucks to tune and worse for idle, absolutely horrible on I6 engine conversions I've done...which may prove your right as it's just dumping fuel into intake at timed intervals instead of timed to DRP... but then again it is twice as much fuel I can't tune out? Sync works sweet!

When my kid gets his truck out of the shop I'm going to do Oscilloscope patterns in the Suburban with a Sync and Async bin and prove whatever it is once and for all...

That is why you can't have more than 12.5ms injector pulsewidth, because that is 1/80th of 1 second.

I've thought about that too. But as RPM increase ms time available decreases?

[gregs78cam]

But as RPM increase ms time available decreases?

ONLY if you look at it as being tied to DRP. If for instance you were to enable Asynch at only WOT, then for as long as you are in Asynch mode it will be dumping fuel at 80 pulses per second, and calculating the PW off of that.

[EagleMark]

What about engine rotation? Time intake valve is open? As RPM increase this time decreases. BPC time is directly tied to this available time.

I'm not saying your wrong or I'm right, just can't make sense of it. I know for a hands on fact Asyn is horrible idle and low RPM tune, but it is firing both injectors so more fuel for higher RPM.

That said I'm trying to get my Sync bin to go Asyn at WOT above 3500 RPM where it goes 100% Duty Cycle. Just haven't figured out the settings yet. My setttings are in that other thread and clearly shows it should be going Async... but does not... EBL does it. But seems they have some issues in the transition. I'd like to figure out the math for all the BPW/BPC Sync to Async etc... settings instead of guessing. Already found the Cop Car injectors don't put out more fuel! They have a lower BPW/BPC so they don't go 100%/Static at 3500-3800 RPM... yes more LB/HR but the lower BPC makes them the same each firing as regular 5.7L injectors.

[RobertISaar]

synch vs asynch =

synchronized to DRP vs not synchrnoized to DRP.

converting the BPW into a duty cycle(instead of a timed burst) is a dead giveaway of asynch. consider this: with synch, the injector pulses happen when the reference pulses happen, maybe a short delay, but they're directly driven by it. with asynch, ref pulses are needed ONLY for the speed-density calc, it doesn't care when they happen, only that they happen. converting to a DC takes away the timing and just flows the calculated fuel while running at whatever speed loop(was it 80Hz?). it CAN work, but there's no real reason for it to be used when you have the capability to run synch.