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Thread: Synch vs Asynch fueling

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    Synch vs Asynch fueling

    EDIT EagleMark: Question moved from another thread.

    Synch vs Asynch fueling...

    Synch fires with DRP. There may be a time delay, but it's DRP--Inj DRP--Inj. Asynch uses a strange method with an accumulator and an internal timer. Each time the code wants some type of quickie extra fuel it sends a request for asynch fuel to the accumulator. If the requested injector on time is less than the minimum asynch pulse value, the request is held in the accumulator. Once the accumulator value is equal to or greater than minimum asynch value, the injector is pulsed on the next cycle of the internal timer and the accumulator is reset. DRP has nothing to do with this one. If the accumulator value = (or is greater than) minimum asynch pulse, the injector is triggered.

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    RIP EagleMark's Avatar
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    Thanks 1project2 many!

    That is strange? I had it wrong as I thought async was both injectors each DRP and Sycn alternated injectores each DRP. Or is that still the case? I can see where async could provide extra fuel if need be, but how would this ever be used at idle, or like I mentioned in other bins that async is always on?

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    Asynch will fire both injectors. For asynch at idle look at AE and stall saver. The Corvair has low vacuum so if there's enough of a change that the ecm thinks the engine's loading up, it might call for AE. Or if there's enough of a surge in idle speed the stall saver might become active. Stall saver usually comes with a bunch of spark advance as well so use that as a clue. I don't believe asynch is ever always on. I think the checkbox allows or prevents asynch at idle. Have you got a mask / cal and maybe I can look through code??

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    We already fixed the Corvair, he started with a fresh bin and idles great now. Besides a lot of things checked and unchecked wrong there was a lot of Items Not Defined, so I don't know what the issue was but it's good now.

    I moved this to a seperate post for info.

    I don't believe asynch is ever always on.
    That was my thought, but I have V6 7747 bins that Async is always on, they run horrible so I took a V8 bin I knew was Sync and made it a 6 and they run great, this was on I6 conversions. I was wondering if there was a reason a V6 needed Async?

    One of those bins (AKSF and AKSK) that runs Async always on is in ony's thread on Lean Cruise, it was a superceded bin and now that he has the updated bin he says it runs much better but I have not seen data yet to see if it is now Sync. I'm very curious...

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    Ony got the data from the updated bin and it's still Async all the time... just don't understand why they would do this on a 7747 V6 cal? The Corviar is running a 97427 V6 cal and it is Sync. Is there a change in V6 engines?

    Then I remembered some? 7747 4.3L had 2 differant size injectors? That alone has always baffled me...

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    I'm not sure what you're looking at. Which location? Which TP definition file? I've looked in TP and TC and I don't see a selection for what you're describing.

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    Well that is kind of the point, there is no parameter for this in $42! But in DATA there is a bit for Sync or Async under all switches. If it weren't for the TunerPro ADX file telling me fueling was Sync/Async I would never have known and continued to tune? Changing to a known Sync fueling bin cures all the issues. Seems every six cylinder bin (or at least all ones I've tried) is Async?

    In $0D they run Sync and at WOT/PE or for some other reason goes Async. I think $42 does the same but it takes a lot more then a stock TBI engine...

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    Well, that's a little different. I'll have to investigate a couple of different cals and the recorded data to see what's causing that.

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    Did a lot of reading today and going through hacks and bins... I just don't understand why any cal would be Async always from factory? It's not just V6 $42 either, there are some 7.4l and even $0D, $0E, $E6...

    Some of the old DIY-EFI posts quote Async as firing every 12.5 Msec and has nothing to do with DRP, this would explain the accumulater/timer and saving some then dumping what's left if not used. Just sounds like a bad way to do things...

    I'm now wondering if a couple rigs I tuned awhile back was a poor choice of starter bin/cal and not noticing this? Never had an issue with 5.7L stuff as I alwas start with ASDU, since then I have used it for everything. One's I had issues with were 7.4L and 4.3L, went back and looked and sure enough they were Async!!! I hate Async!!!

    Because of all the research today $42 ended up with a few more paremeters, most importantly 2 BPW times, with these you can now spot an Async always bin... also filled in at least 100 descriptions in paremeters. All my notes from papers written, posts found and all my personal finds, it's like an EFI tuning dictionary now!

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    How can you tell a async only bin from a regular bin?
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

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    Until I do some testing on these $42 bins the only way be sure is data log.

    But if you look at this picture and compare you will see the differences, bin is Async, compare bin is Sync.

    Sync is so easy to tune and idles so much better...
    Attached Images Attached Images

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
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    Looking through $42 hack it's easy to see how Async could be used to calm down injector pulse at idle or add fuel at WOT. At 2400 RPM it is 1.0 so even, under that it is taking away and over that it is adding.

    Also makes it impossible to watch Injector Duty cycle?

    Code:
     ;----------------------------------------------
    
    ; ASYNC MULT vs RPM TABLE
    
    ;
    
    ;
    
    ; THIS MULT IS USED TO CONVERT SMALL PW
    
    ; (PW/CYL)TO ASYNC (PW/12.5 Msec) INJ.
    
    ; FOR ASYNC INJECTIONS
    
    ;
    
    ;
    
    ; ASYNC IS BOTH INJECTORS, SYMO
    
    ; SYNC IS ATRNATING INJECTIONS
    
    ;
    
    ; FACTOR = (NUM CYLS/2) * (RPM/60) * (0.0125/2)
    
    ; .0125 = PULSE PERIOD, (80 Hz)
    
    ;
    
    ;
    
    ; TBL = MULT * 64
    
    ;----------------------------------------------
    
    LD46B: FCB 8 ; 9 LINE TABLE
    
    ;
    
    ; MULT RPM
    
    ;----------------------------------
    
    LD46C FCB 0 ; 0.000 0
    
    LD46D FCB 21 ; 0.328 800
    
    LD46E FCB 43 ; 0.672 1600
    
    LD46F FCB 64 ; 1.000 2400
    
    LD470 FCB 85 ; 1.328 3200
    
    LD471 FCB 107 ; 1.672 4000
    
    LD472 FCB 128 ; 2.000 4800
    
    LD473 FCB 149 ; 2.328 5600
    
    LD474 FCB 171 ; 2.672 6400
    

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
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  13. #13
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    Quote Originally Posted by EagleMark View Post
    Also makes it impossible to watch Injector Duty cycle?
    depends. if it's done entirely on the 80Hz loop, you know that 80 times per second, the BPW displayed is being injected.

    if it can flip between 80Hz async and sync, then you'll have a really tough time dealing with it.
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    OK, but what about the mulitlier? it starts at .328 to 2.672 depending on RPM... I don't even want to think how to make a Injector Duty Cycle % gauge for that!

    This whole Sync - Async thing started awhile back for me until I noticed it in Data, then realized Sync was so much easier and smoother. Then this summer I tuned a Jeep engine conversion and noticed the Async always? Swaped bins and viola! POOF! Good runner and easy tune. Since then he told another Jeep buddy with a TBI conversion and sure enough another Async system, started with new bin and POOF! Good runner and easy tune. I thought it may be a GM V6 engine needing this and issue to the long intake runners of a Jeep engine? Still have not had my hands on a GM V6... but I have screwed up a perfectly good tune in my V8 Suburban trying to get an Async tune to run. No way to get it even close to running as well as Sync?

    So I'm back to my origanal question, why Async?

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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    that table is a straight line(and shouldn't ever be changed actually).... could be taken care of in the equation easily.

    why run async? the only reason i would see it being needed is if you didn't have a good reference pulse interrupt subroutine setup or even capable(a lot of old code gets recycled, possibly code so old that it was used with a processor that didn't support external interrupts?) of firing the injectors based on anything other than a timer loop.

    or perhaps it was GM's way of not needing multiple injector pulses to get AE fueling in when needed?

    in any case, avoid. fix when possible, start over when not.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


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