In regards to the 80 Hz async firings for async with TBI, think instead switching to firing an injector every other DRP (IOW, 4 DRPs per each injector firing rather then 2 on a V8) work as well? On one hand it seems like it could as the PCM is going to skip firings in async, anyway, to accumulate enough pulsewidth to fire the injectors. On the other hand, the async firings will likely happen more often at low RPMs, so the manifold may not get as dry in between firings.

Id like to add a more elegant method of MPFI support to the TBI PCM, but currently the async is a bit of a mess. In the PCM, there are three seperate controllers for the injectors. The hardware level and async controllers like the old ECMs, and an interrupt driven controller that is triggered within the software. Switching async modes for the TBI would clean it up alot. On the software side, going to MPFI would instead just be a matter of setting an option byte to '1' and the software would automatically adjust the firing rate based on the # of cylinders the engine has. TBI would be alt fire while the other modes would be bank fire.

 

We did that on small displacement 4 cylinders (single TBI injector) with good results, but not perfect of course. The idle emissions increased a little, signalling that the cylinders weren't getting perfectly even distribution. The flow from the injector was very stable and helped idle a lot, though. This wasn't compared to GMs 12.5 ms interval async, though, so I can't say if it's better or worse, but it definitely was better than plain sync.
I think the P4 ecu has a good alternate fire mode description in the hack that's been around and back.
When doing async like this, it's CRITICAL to get the injector vbatt offset darn close. Also need a wide hysteresis of PW to avoid going in and out and in and out of async mode.

 

More than anything else, the async in TBI mode will be a last ditch effort if the pulsewidth gets really low. Its better then having the PCM just dump the pulsewidth altogether if it gets too low.

Not having the 80 Hz async will make the code much more modular. All the firing modes will work as bank fire, just that the interval will increase in MPFI. Before, they had the rate set within the memcal, which set a flag in the code, which triggered teh injector firings. Sort of messy and round about when the rate can be just set in the code.

 

lol...

its things like this that still give me hope....

on one hand, theres the logical side of "why the hell are you even thinking about this? and why not just run a megasquirt,GMPCM, ect..


on the other hand...... i totally get the cool, and fun factor of figuring out how to "make this work"... we know its theoretically possible.. now lets figure out how to do it. lol.

 

No offense, but your post makes no sense and its way out of context. I dont know whether to be offended, or just confused...

 

It just CONFUSED me. Since when did Megasquirt arrive to the same level as a GM PCM. The TBI PCM can control coil packs and an electronically shifted transmission too.

 

When I was playing with the $8D and the 730 I had thoughts about doing async at low RPM, low BPWs. The idea was to use single fire mode and base it off of the 720* crank rev time so that I could get the injector firings as close as possible. This is using the $8D with large injectors and small cams. Using double fire batch results in BPWs that are too small, and single fire has a long time between injects.

What this led me to was the fact that I need alternate bank firing. That is, squirt all of bank 1 for the first crank rev. Then squirt bank 2 for the second crank rev. It makes the time more evenly spaced and you can still go to double fire batch when the BPWs get too high. All that is not possible with the 730, but the 427 has the hardware and as you pointed out it is all under software control. Just something to think about if you want to go straight sync BPWs.

EDIT: The other thing I was thinking about doing was using single fire mode and a BPW predictor much like the spark advance predictor works. A Kalman filter was in the works for the BPW predictor. I ditched it all when I read about the 427 ECM and the hardware it had. Although, that stuff could be done async alternate bank fire with the Kalman filter in the 427.

 

Im going to be doing what you described with the code. One bank firing per revolution. Id also like to add some sort of signal processing as well for the BPW. The BPW will be calculated as though the PCM where firing in SFI with only one injector firing at a time. But, four injectors will be firing every rev (or 3, or 2, depending on the motor) Id like to at least average the PW over that interval to keep the idle from getting lumpy. I wonder if just averaging the PW over one rev would be sufficient, or if something more would be needed?

Also, where is the Kalman filter? Is it that big complicated one thats used for the TIS filtering?