Synch vs Asynch fueling

[EagleMark]

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?

[RobertISaar]

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.

[EagleMark]

You just made a lightbulb go off! So does Async use DRP or not? If not it would work on a conversion without need for tach filter or GM ignition EST module...

[RobertISaar]

yes and no....

yes because to do the speed-density calc(and therefore determine the amount of fuel to inject), speed(RPM) is required.

no because it doesn't fire based on where the crank/pistons are at, only based on time.

at 80Hz, 12.5mS is 100% injector DC

[POZE]

In the synchronized mode of operation, the injector is pulsed once for each distributor reference pulse. In dual throttle body systems, the injectors are pulsed alternately. In non-synchronized mode operation, the injector is pulsed once every 12.5ms or 6.25 ms depending on calibration. This pulse time is totally independent of distributor reference pulses.

Non-synchronized mode results only under the following conditions:
When the pulse width is to small to be delivered by the injector (approximately 1.5ms ).
During acceleration enrichment.
During deceleration leanout.

This is information came from a GM book published in the late 80's.

[POZE]

With a scope you could compare the IPW to the DRP and verify async vs sync mode.
On a TBI simulator running at a steady speed, if the TPS is quickly opened and no DRP change you will hear the injector being rapidly pulsed. You can do the same thing on a running engine and hear the engine drop rpm's because of the added fuel. I guess that added rapid pulse (AE?) would be asynchronous.

[1project2many]

In non-synchronized mode operation, the injector is pulsed once every 12.5ms or 6.25 ms depending on calibration.

It's always amazing just how much GM engineers just handed out in the repair manuals and instructional books in the '80s. This variable can be configured in software and it can be helpful to adjust it when using injectors that are dramatically different from what the calibration was designed for.

With a scope you could compare the IPW to the DRP and verify async vs sync mode.

In the service bay I used to use a timing light attached to #1. I could see which TBI injector was synched with #1, which fired alternately, and it was very plain when asynch was operating. It was a good way in the early days to check injector pattern and quality. It's funny how, after enough years, you learn what things are likely to be a problem and which are not. I haven't bothered doing that with TBI in years. They fire or they don't.

Some software, most notably $58, has a quasi-asynchronous mode as well. This mode is used when IPW is too small for the injector. The Injector will be fired for 2X IPW but 1/2 as many times. Getting the transition right can be tough and in the SYTY world there are plenty of guys that have forced quasi-asynch at all times in order to avoid tuning at the transition.

[Ronny]

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.

When i first modded my engine adding 75 lbs inj's at 13 lbs FP I witnessed surge at idle. I was told(RBob) to disable asynch partly due to my TPI pump having adequate supply of fuel for WOT. I thought it was reducing the pulse rate by half by disregarding the DRP every other injector pulse. Now I see it actually was a multiplier to injector pulse width.

ASYNC IS BOTH INJECTORS, SYMO
; SYNC IS ATRNATING INJECTIONS;
; FACTOR = (NUM CYLS/2) * (RPM/60) * (0.0125/2)
; .0125 = PULSE PERIOD, (80 Hz)

So by going all synch at idle it will achieve less fuel than asynch? Or is it the cycle repeating of synch to asynch that causes the surge? I bet that is the reason for surge. My result was a richer idle(WB) witnessed but stable idle.

[EagleMark]

If it's $42 then just start with a Sync bin like ADSU auto or ASDX manual.

There's lots of other things that can cause surging as well, biggest is a vacuum leak. Built motors can be several settings in bin.

[Ronny]

It has been eight years since I ran a 7747/$42. this is Ronny from 3rd gen BTW.

[EagleMark]

Bought time you came by!

[907 Chevy]

So I'm still trying to wrap my mind around this... asynch is a good thing when using larger injectors at idle due to pulsewidths becoming to short in synch mode? That about right?