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Thread: DIY LTCC or similar system for LT1s

  1. #151
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by kur4o View Post
    If you unset high res dtc bit at 12029 bit $10, you may try again runnig with high res disconnected.
    I am pretty sure it will at least fire up and all the calculations will be time based on the low res signal. It will work just like the older distributor system with coil pick up signal. Of course spark scatter will be higher and timing will be not very accurate and we will lose the great starting time of less than a second.
    None of this compels me to want to code to time based sequence detection. At least not for a proof of concept. What are your thoughts? Does the Delteq system require high res?
    '95 C4 LT-1 ZF-6, Polo Green
    Comp 467 / XFI 280, UltraProMag RRs, LE1 Heads, Lunati 73925 Springs

    Somebody stole the spark plugs out of my other car, yet it still runs???

  2. #152
    Fuel Injected! vilefly's Avatar
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    Just confirming obd-1 status. I will see if I have time to see if my 95 caprice does anything different. probably next week I might have the time at work.

  3. #153
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    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.
    Last edited by kur4o; 3 Weeks Ago at 03:40 AM.

  4. #154
    Fuel Injected! vilefly's Avatar
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    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.

  5. #155
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by kur4o View Post
    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.
    '95 C4 LT-1 ZF-6, Polo Green
    Comp 467 / XFI 280, UltraProMag RRs, LE1 Heads, Lunati 73925 Springs

    Somebody stole the spark plugs out of my other car, yet it still runs???

  6. #156
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    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.

  7. #157
    Fuel Injected! vilefly's Avatar
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    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.

  8. #158
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by vilefly View Post
    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.

    Quote Originally Posted by vilefly View Post
    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.

    Quote Originally Posted by vilefly View Post
    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.
    '95 C4 LT-1 ZF-6, Polo Green
    Comp 467 / XFI 280, UltraProMag RRs, LE1 Heads, Lunati 73925 Springs

    Somebody stole the spark plugs out of my other car, yet it still runs???

  9. #159
    Fuel Injected! vilefly's Avatar
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    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.

  10. #160
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by vilefly View Post
    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.

    Code:
    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.
    '95 C4 LT-1 ZF-6, Polo Green
    Comp 467 / XFI 280, UltraProMag RRs, LE1 Heads, Lunati 73925 Springs

    Somebody stole the spark plugs out of my other car, yet it still runs???

  11. #161
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    That`s it. Ltcc measures the time between low res pulses and calculates rpm. Than use simple lookup table [rpm] vs [low res pulses till BTDC] to start charging the coil.

    low res pulses till BTDC=at tdc counter is reset for current cylinder and you have 7 low res pulses till next ignition event.

    Here are some formula [60*1000] / [x*4]=rpm
    60=60 seconds in a minute
    1000= to convert in ms
    x= time for 90* cranshaft rotation or time between low res pulses
    4= to get 1 crankshaft revolution time

    2.5ms/90 = 0.0278ms for 1 degree rotation at 6000 rpm

    46 total advance = 1.27ms error at 6000 rpm for dwell time. which is acceptable since dwell can vary.
    Since nobody runs anything between 20 and 38 at high rpm that error can be brought down.

  12. #162
    Fuel Injected! vilefly's Avatar
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    spfautsch,
    I am not sure if the LTCC unit has its own spark tables, but it has its own spark-retard tables and settings. I cannot say if it changes timing during normal, non-knock operation without proof for myself. I grant you it would be cheaper not to bother with it.
    But it seems rather certain that it does not control dwell time, only divides it by 8 by selecting coils. If you take the stock dwell time, and give each coil 2 revolutions before the next fire, you will have solved any dwell problems easily without the need to modify anything. Now, you can magically rev beyond stock speeds. Cheap and easy.
    As to the lack of power above 5500, that depends if you are using a stock cam or not, or outrunning your injector flow rate/on-time. I don't know any specifics on the engine you mention, unless it is the one listed under each of your posts. The science of dwell time is no mystery to me, but it never hurts to review. Injector on time can pose major problems at high speed, though.

  13. #163
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by kur4o
    That`s it. Ltcc measures the time between low res pulses and calculates rpm.
    Don't you think measuring / tracking spark advance would be necessary also?

    Quote Originally Posted by vilefly View Post
    I am not sure if the LTCC unit has its own spark tables
    I'm more than a little sure it doesn't. More directly the ECM controls spark advance, which is why it requires a signal from EST. Otherwise anyone with a LTCC would have to customize the spark tables for their own tune.

    Quote Originally Posted by vilefly View Post
    If you take the stock dwell time, and give each coil 2 revolutions before the next fire, you will have solved any dwell problems easily without the need to modify anything.
    You also create a condition where you have a bunch of coils that are energized all the time and will all spark simultaneously the moment the ignition circuit is cut.

    On top of this, wouldn't coil overheating be a concern?

    [edit: or did I misunderstand your suggestion here]

    Quote Originally Posted by vilefly View Post
    As to the lack of power above 5500, ... The science of dwell time is no mystery to me, but it never hurts to review. Injector on time can pose major problems at high speed, though.
    The point I was trying to make is that the stock setup has very little dwell time capacity at higher RPMs and spark advance. Or am I mistaken?

    The only way I can forsee doing something like this "easily" with an Arduino compatible uc would rely heavily on the high-res signal, using dwell lookup tables and keeping everything in terms of degrees so the uc can track by the high-res count. Unfortunately it still needs to be able to measure the time between low res pulses to four or five decimal places or RPM [edit: and spark advance] calculations are going to be horribly inaccurate. So three inputs that all need relatively precise and fast ISRs, and time to within 100us, possibly 10us. All this is well outside my comfort zone.

    Attached is the sketch as I left it yesterday. It has not been tested but does compile. If it's of any help take whatever liberties you'd like with it.
    Attached Files Attached Files
    Last edited by spfautsch; 2 Weeks Ago at 01:58 PM.
    '95 C4 LT-1 ZF-6, Polo Green
    Comp 467 / XFI 280, UltraProMag RRs, LE1 Heads, Lunati 73925 Springs

    Somebody stole the spark plugs out of my other car, yet it still runs???

  14. #164
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    Here are some threads with pictures.

    https://www.youtube.com/watch?v=_8JrLEso7Vg at 0:56

    http://www.dw-zone.com/ltcc/LTCC1.jpg

    So ltcc have different board revisions.

    https://encrypted-tbn0.gstatic.com/i...mWbfWgxK6HQx-X

    And the delteq unit.

  15. #165
    Fuel Injected! spfautsch's Avatar
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    I recognize that microcontroller package but it's from waaaaaay before my time (in the realm of ucs).

    I think before I jump to any more conclusions I'd like to see a scope capture of the following signals.

    EST
    LowRes Opti
    Inductive clamp on #1 spark
    #8 Injector (or #4 or whichever gives best waveform capture for kur4o's request)

    Both at idle and holding at say, 4000rpm.

    If that's not something you can do any time soon vilefly, I'll look into doing it. I wouldn't mind owning one of the little capture devices you posted, even though my toy fund is currently deep in the red.
    '95 C4 LT-1 ZF-6, Polo Green
    Comp 467 / XFI 280, UltraProMag RRs, LE1 Heads, Lunati 73925 Springs

    Somebody stole the spark plugs out of my other car, yet it still runs???

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