Synch vs Asynch fueling

[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.

[1project2many]

What's tough about IPW isn't displaying actual value... it's relating it to numbers you're used to seeing. There's a flag for synch / asynch operation which you could use to know which mode is operational.

I've never noticed an "asynch only" cal and I've made plenty of BBC based cals over the years. I'll have to think about why the values would be set as they are.

[RobertISaar]

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.

that's an understatement.

all of the MPFI 60V6 programs have this capability.... i tried to get the transisition to work correctly for weeks and ended up just running full-time single-fire.... then after a while, went back to double-fire, didn't really see a difference between the two, but i was also playing with some really small injectors(16.7 lb/hr).

problem was that while some transitions worked correctly, other times a normal single-fire injector pulse would happen, followed immediately by a double-fire pulse, making the entire engine go super-rich for a cycle or two. felt bad with the TCC engaged. never could find that bug in the software that caused it.

[EagleMark]

I've never noticed an "asynch only" cal and I've made plenty of BBC based cals over the years. I'll have to think about why the values would be set as they are.

AZFT is an updated bin from superceeded ???? and it's times were cut in half, but not quite as low as what I pictured below. I think it was Async may be a Sync/Async now? Jims new dissasembly IIRC has recommented some Aysnc to Sync in code and before I read that I found the other two BPW times and added them to $42 mask.


Compare bin is Sync fueling...

[EagleMark]

I don't do much data logging with DFCO, PE, EGR etc... so I never noticed. But DFCO is Async! (7747 $42 Sync fueling bin)

[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?

[Ronny]

I believe synch is better for larger injectors for idle. I am thinking that if asynch is allowed the ecu moves form synch to asynch in a rythmic pattern causuiing a surge. Pulse width is constanting oscillating. For PE WOT asynch I believe will work but if you have adequate inj size and or FP then synch may be better. You cant have both
synch and asynch.

Downside of using synch only is ecu may not be able to command a desireable A/F as there is a limit as to small a PW is possible. I recall discussion as to the maximum PW being around 7.0 msec but have not seen any comment on minimum PW. There is also proportional gains that may need to be reduced to allow a very short PW. Mine are about 50% less than stock L03(inj's75 lbs at 26 lbs FP).

As pointed out a surge can be caused by vac leak or lean. Other tools exist to steady idle. Try varying SA to determine what works best for you. Make all SA around your idle cell the same SA. Lock SA for idle. Consider idleing in open loop at a richer A/F. Some masks allow the above others do not.