What does the async to sync threshold and sync to async threshold vs map/rpm do (diffrent values in bjym to my bjlk).

I think my cam and rear end ratio(3.08) vs trans 0.70 is the pain in the *** for fuel mil(or my foot).

Going to try change the shift points and lockup to higher mph/rpm
to see if it lower the dc a bit

 

Those thresholds determine when the injector firing scheme switches from synchronous (injectors fire alternately with each DRP) to asynchronous (injectors fire simultaneously at 40 cycles per second) and vice-versa. In my experience with this PCM, those thresholds have no bearing on fuel economy or drivability. Some $0D bins only use synchronous mode at idle and asynchronous off idle with no issues. HTH

 

I think its 80 Hz since thats the speed the loop updates the PW, not that it really matters for the topic at hand.

Im not quite sure why they switch to async when off idle using all those threasholds but Id say its to spread the firings out and increase the available firing time since a lower percentage of time will be needed for opening/closings. You could probably just use sync firings most of the time. With the old computers, async was used so the ecm could withold firings if the PW was too low but IIRC, thats no longer the case. Id have to go back and see for sure.

 

Has anyone verified that it ever goes into async mode?
I only see aynce being necessary for AE when it needs "to be done quick" or when big fuel injectors are used. The factory never used real big injectors though.

 

What do you mean "done quick"?
I don't see async being necessary... ever...
To do AE, just add it to the final pulse width. If the pulse width gets so high that the injector is static then the remander is carried over to the next pulse width.
Honestly, I think the guys programming the TBI ecm/pcm's might not have been the brightest bunch of guys. From the looks of the code vs other code I'd say they weren't getting much help from the smart ones . Either that or there was a conspiracy to keep TBI from EVER becoming a hot rod solution.
In reality there is very little if any measurable difference between using async vs sync so long as the calculations are done correctly and the same amount of fuel is delivered.
Maybe, just maybe, the later TBI pcm's used async off idle to get rid of the AE async vs sync missing fuel problem . Either they knew it was there and decided it would just be easier to run in full async OR they didn't know it was there and were beating their heads against the wall until somebody made a robust choice to run async all the time.

 

What he said. . .

RBob.

 

FWIW it is only the V-6 applications, TBI and CPI, that go asynch immediately off idle from what I have seen. The V-8 TBI applications stay in synch til around 2k RPM and about 85 kPa MAP. That would kinda tend to disprove the "spreading out the firings" theory as there is 25% less DRP's/RPM, hence 25% less firings per RPM with a V-6. The AE routines seem to work well although I cannot say the same for the calibrations (MAP AE is seriously lacking in the cals) even though it is asynch so I cannot, for the life of me, figure out why GM did this. Maybe they were just lazy.

 

I really don't know much about this stuff. At 1000rpm it would be about 20ms between DRP on a V6. Done quick would be adding fuel for AE at a rate of 12.5ms instead of 20ms. That is "done quick". Not fact, just my theory.

 

I lookt at my 94 bjlk 6395 vs 95 bjyk bin 7427 (350 lo5).

Async to sync fuel rpm thresh = bjlk 1200 rpm (2000 rpm bjyk).

sync to async fuel rpm thresh = bjlk 1300 rpm (2100 rpm bjyk).

Async to sync fuel map thresh = bjlk 45.78 kpa (81.20 kpa).

Sync to async fuel map thresh = bjlk 51.68 kpa (87.11 kpa).

This is the only async and sync values thats diffrent.

 

It kind of seems opposite to me - are you sure there isn't a mistake in the .ecu or .xdf?

Typically Async would be used at low loads, not high.

Has anyone measured the PWs with an oscilloscope to see if it's correct?

 

I compared the bins with tunerpro rt same xdf.

bjlk = 3.73

bjyk = 3.08

 

The settings are correct. The "synch at idle" bit is set so the paramaters reflect the hysteresis of going out of and and back into synchronous mode. HTH

 

I have verified that it does indeed work as said above via hacking the code.

The only reason I can see is to increase the available PW at high RPMs while allowing for use of injectors small enough to give reasonable PWs at low loads/idle. In the older stock fbody tbi cals, the DC was in the low 90's, so theres definatly evidence that they where trading off DC at high rpms for DC at idle. Having async frees up a few more percent at high rpms.

 

Dude, no flame intended. I agree with your theory about high RPM operation and bieng able to get more from smaller injectors, but that doesn't answer the question of running asynch just off idle and only on the V-6 stuff. Do you have a theory on that?