DIY LTCC or similar system for LT1s

[kur4o]

How about the dwell time of ls1 coils. They need to be charged between 3.5-5ms before they fire. If we use pcm signal as a spark trigger, the coils should be already charged in advance, so they can fire at the correct time. Guessing is not an option here, so how do we calculate properly in advance start time of coil charging.
If we can you measure the time between the icm recieving spark signal from the pcm and the coil firing, we can put this time into account.
I hope it can be spread by software calibration in pcm.

Low resolution signal measures time between 90* crank rotation. 19ms are around 750 rpm and 2.5ms around 6000 rpm. It is used as a source for rpm calculation for PCM. This is the conversion formula
x=word_a1[eside]
983040/x = rpm
0.015234*x = msec.
Half of the pcm calculation depends on correct RPM value.
Without any low res opti signal PCM is doomed.

Vilefly can you remember when you make that awesome graph at page 8-9, what was the car coolant temp at time it was taken.
I am trying to find and confirm End of injection time constant but without the proper scope tools it will take indefinite time.

[vilefly]

All my posted waveforms were done with a warmed up engine. 196-224 deg. F. I try to do all mine at this temp range to remain as consistent as I can.

[spfautsch]

How about the dwell time of ls1 coils. They need to be charged between 3.5-5ms before they fire. If we use pcm signal as a spark trigger, the coils should be already charged in advance, so they can fire at the correct time. Guessing is not an option here, so how do we calculate properly in advance start time of coil charging.

I hadn't taken charge / dwell into consideration. This complicates things - at higher RPMs the coils will need to be charged two low res pulses ahead of firing sequence, before the preceding cylinder will be firing. And then there's spark advance to consider, and evidently also primary voltage. This puts things way out of my league as far as time constraints go. Essentially this becomes an ignition computer instead of a simple sequence controller.

[kur4o]

Ltcc somehow managed to overcome that obstacle. I wonder if it works as it should be or there are some shortcuts. Anyone with ltcc experience can share how it works.

Vilefly thanks alot for the shared info. It really helps alot.
It partially confirms my theory how end of injection target works.
At b-body bins at warmed engine it is $50 which might be 5 low res pulses before TDC, exactly as seen on the graph.
If you want to contribute a little more, you can play with low res signal and #1 injector pulse at the scope. The coolant should be below 32*C at startup.
If my assumptions are correct the end of injector pulse will move slowly from 4 low res pulses bTDC to 5 low res pulses slowly as the engine warms to 44*C.

I have a cold starting log. The engine starts after 300ms cranking at 10*C coolant. It took two low res pulses to syncronise before starting.

[vilefly]

I suspect that the LTCC module simply lets the original ECM run the coil dwell time. I will attempt to prove that the ECM controls coil dwell time, not the Ignition module with a waveform if I can find the time. Something like EST signal vs primary waveform.
As to controlling dwell time yourselves, I suspect they use a simple lookup table instead of real-time calculations that would slow everything down. You guys would know more about that than I would, though. One thing I learned from messing with ECM strategies externally is that they run the engine on a dyno with cylinder pressure sensors on each cylinder so they can put the info all into lookup tables so that the cheapest processor can be used to run the show.
The Delteq has a UV eprom in it, and I still wonder what is on it. I believe its lookup table should mimic my northstar data array in pattern, at least.

[spfautsch]

I suspect that the LTCC module simply lets the original ECM run the coil dwell time.

Is this module still available? I don't see any technical data about it on his website and most of the links are dead.

I will attempt to prove that the ECM controls coil dwell time, not the Ignition module with a waveform if I can find the time. Something like EST signal vs primary waveform.

Even if it does that's somewhat irrelevant, because we would still have to maintain a real-time picture of RPM and commanded spark advance in the uc to be able to provide adequate coil charge time while avoiding overcharging / overheating the coils.

As to controlling dwell time yourselves, I suspect they use a simple lookup table instead of real-time calculations that would slow everything down.

Even with lookup tables for dwell you still have to calculate RPM, advance, and ideally supply voltage to know what to lookup. I believe this may be possible with a 16mhz avr, but I'm not sure I trust myself to write the code to maintain accurate spark to 6800rpm with a $25 microcontroller.

[vilefly]

I found the LTCC installation instructions here. https://www.camaroz28.com/forums/lt1...ns-new-882760/

I noticed it requires the EST signal to function, as well as hi/low res signals. If it truly controls dwell by itself, then it would have no need for the EST signal at all. It probably takes the EST signal, measures the pulsewidth and stores it, multiplexes a pulse to the correct ignition coil driver and fires the coil at a stock pulsewidth/dwell time.

If I had to, at gunpoint, reduce the dwell time, I would send +300v to the primary of the ignition coils. Works for MSD. Or maybe just 24v. Lie once, cheat twice.

Oh, something else the LTCC unit does......flash codes with green light to identify failure conditions. Seems to complain if the key is toggled inside of 5 seconds for some reason. This is what I have been able to find out so far.

[spfautsch]

If it truly controls dwell by itself, then it would have no need for the EST signal at all.

EST being the white wire? Are you implying the LTCC module has it's own spark advance tables?

Adding a buck-boost circuit to power the coils with > 14.4v adds part count and would significantly increase cost. Considering this and the difficulties I see in writing the controller firmware, the LTCC module seems very reasonably priced. I may just buy one eventually but right now my toy fund is severely depleted.

If I had a way to produce a cad drawing of the trigger wheel quickly I'd draw up some graphics to illustrate. But I just don't have time. Here's the best I can do with words.

Let's assume some generic constants - 5ms coil charge time, and 30 degreees spark advance. 1000RPM idle and 6000RPM wot with these same constants. Please double-check my math.

RPM            1000        6000
Crank Rev. Time (360d)    60ms        10ms
Cam Angular Velocity    0.333ms/d    0.0556ms/d
Cam deg - 5ms dwell    15 deg        90 deg
Spark advance in ms    4.995ms        0.834ms
Cyl 1 Dwell Strt (cam)    30d btdc    105d btdc
Cyl 1 Dwell Strt (crnk)    60d btdc    210d btdc

What I'm hoping you take from this is that at 6000 rpm the #1 coil pack will need to start charging 15 cam degrees before the #2 low res slot is encountered, or approximately the same time the #2 coil is fired. And 30 degrees advance at 6k rpm is fairly tame at 100kpa.

This has been a very valuable learning experience. I've learned that the factory coil must have really low impedance and charge time. At the same time I can't help but think I'm probably losing power above 5500 rpm due to weak spark.