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Thread: DIY LTCC or similar system for LT1s

  1. #166
    Fuel Injected! vilefly's Avatar
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    "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?"

    Naw. You're just overthinking it like I did earlier. All I meant was that the on/off signal for the stock, single coil would be rotated through the 8 coils in sequence. None of them would be on until the transistor was switched on by the redirected EST signal. This would be plenty of charge time for a coil running 12.5% as much as the original coil. This is the basis of my non-processor approach to the problem. Just GATE the signals to the right coils at the right time. No calculation. No changes. Just sequence the gating so that it "arms" the right coil transistor at the right time. I have no intentions of going beyond this. You have plans to do so, I bet, and there's nothing wrong with running 2 arduinos to accomplish what you need to do. One to calculate, one to act on it. 2 arduino pro minis don't take up much space. (5v-16mhz versions) I don't know for sure if it would be fast enough, but at $5 each, it would be nice.

    I have weekends off from work, and away from the best scopes. I have only 1 old 4 channel Interro PDA scope with a small black/white lcd display. Probably have to take a picture with my phone to get a decent capture. Or.....I could try for the next work week when I have access to everything. Either way, I will see what I can do.

  2. #167
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    Quote Originally Posted by vilefly View Post
    So, Johnny, how's the northstar ignition module working for you?
    Haven't had much time to play with anything, as I have about 5 weeks left in the semester.

    Given Kur40 knowledge of EE if he thinks the northstar icm is a step back then it most likely is so I have abandoned that idea.

    I'm still lurking on y'alls discussion though

    good luck guys

  3. #168
    Fuel Injected! vilefly's Avatar
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    Quote Originally Posted by johnny_b View Post
    Haven't had much time to play with anything, as I have about 5 weeks left in the semester.

    Given Kur40 knowledge of EE if he thinks the northstar icm is a step back then it most likely is so I have abandoned that idea.

    I'm still lurking on y'alls discussion though

    good luck guys
    I tend to look at it as a half-step towards 1 coil per cylinder. It still eliminates the hi-voltage side of the optispark, which is the goal of all these
    experiments. I would not use it for a top-fuel dragster, but on the street, sure.

  4. #169
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by vilefly View Post
    All I meant was that the on/off signal for the stock, single coil would be rotated through the 8 coils in sequence. None of them would be on until the transistor was switched on by the redirected EST signal. This would be plenty of charge time for a coil running 12.5% as much as the original coil.
    This makes the assumption that the LS coils have electromagnetic properties that are similar to the Opti / HEI2 coil, and I think that's a flawed assumption. If you recall back to this post the auto companies put a lot of effort into sourcing the cheapest components that will get the job done. I'm sure the LS coil selection received the same due diligence. If they knew they had two full engine revolutions to provide adequate charge time I'd bet that heavily influenced the type of coil that was chosen. I haven't been able to find any specs on the HEI2 coil or driver module to compare, but what I was hoping to see with the waveform capture at idle and then 4k rpm is a rough picture of dwell at different speeds. I would imagine there's a dwell table in $EE but I haven't had a chance to dig through all the .xdfs and the disassembly looking for it.

    Quote Originally Posted by vilefly View Post
    This is the basis of my non-processor approach to the problem. Just GATE the signals to the right coils at the right time. No calculation. No changes. Just sequence the gating so that it "arms" the right coil transistor at the right time. I have no intentions of going beyond this.
    And that approach might be perfectly adequate up to a certain RPM. But I doubt many of the LT-1 enthusiasts would care much for an ignition system that performs worse than a properly functioning Opti.

    Quote Originally Posted by vilefly View Post
    You have plans to do so, I bet, and there's nothing wrong with running 2 arduinos to accomplish what you need to do.
    I haven't ruled out the possibility but it's certainly looking more and more like a scenario where the the LTCC module is a much better value than what I initially thought. The only thing I would gain by spending all the time and effort to do it on an arduino platform is having the code open-sourced.

    In looking for more intelligence on the subject I ran across this article that seems to hint the opti system is heavily reliant on the high res signal for controlling spark advance in real time during cranking when angular velocity is least stable. There's even a heading where they discuss time versus angle based ignition.
    '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???

  5. #170
    Fuel Injected! vilefly's Avatar
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    Well, I didn't get a chance to get a scope capture for you yet. I will try this week at work, but we are hammered with cars so ugly, a genius couldn't sell them. It's "resurrection season" at the shop. Blech. It will be later in the week, if possible.
    I know it drives everyone crazy that I play "slop" pool, but it gets me through the tedious things without a proper education. heh. It's from racing around in my youth with "claimer" engines, and such. Get it running, then fix it. Bass ackwards. Infuriating to those who follow proper procedure, for sure.

  6. #171
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    An interesting find from a 94 service manual.
    Attached Images Attached Images

  7. #172
    Fuel Injected! vilefly's Avatar
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    AH HA! Just as we suspected! Thanks kur4o.
    EST controls dwell.
    Loss of Hi-Res signal = still runs.
    Loss of Lo-Res signal = does not run.
    Limp mode is most likely simultaneous double-fire injection.
    I will still gather waveforms when in limp mode, though.

  8. #173
    Fuel Injected! spfautsch's Avatar
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    Here's a really good writeup on the LS coils. Describes how the dwell requirement changes with input voltage. Also states they have internal current and dwell limiting.

    Curious, does anyone know the cpu clocking of the 8051 and 1333 PCMs? The only spec I've been able to turn up is the flash size.
    '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. #174
    Fuel Injected! vilefly's Avatar
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    Is there a dwell setting that is accessible with $ee hack?

  10. #175
    Fuel Injected! spfautsch's Avatar
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    I assume you mean in the PCM firmware (referred to as the $EE mask for 94-95 model years), and not that I've been able to discern. All the documentation we've seen indicates it's controlled by the EST output but I would have to defer to kur4o or someone else who has the intestinal fortitude to stare at the disassembly because I simply lack the willpower.

    I've found an interrupt triggered capture function available on the Atmegas that might allow for calculating RPM accurately enough to suffice, but a lot more research is needed. One thing I can say for certain is whatever I might be able to come up with will not function whatsoever without the high res signal.
    '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. #176
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    There are plenty of unidentified parameters used by tpu processor.
    It runs from some built in memory ROM but uses some of data in the bin as calibration parameters.

    I figured some high res counters in the code, thanks to service manual opti error descriptions.
    Finding dwell parameters without TPU processor main code will be a guess work.
    Some waveforms from the est signal might help alot though.

    PCM calulates spark:
    1. angle based when high res signal is present{high res counter {possibly triggered after low res rising edge} + {90- spark advance}
    2. time based when high res error is set( in ms after low res pulse is detected}.

    68hc11f1 is 4mhz. I cant find a pic of the crystal used on the board to confirm.

  12. #177
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by kur4o View Post
    There are plenty of unidentified parameters used by tpu processor.
    It runs from some built in memory ROM but uses some of data in the bin as calibration parameters.
    Like a mask ROM? There's generally no way to dump something like that, right?

    Quote Originally Posted by kur4o View Post
    I figured some high res counters in the code, thanks to service manual opti error descriptions.
    Finding dwell parameters without TPU processor main code will be a guess work.
    I was afraid that would be the case. This goes way beyond my propensity for machine code hacking. The deepest I got into this type of thing was dumping avr firmware from a smartcard "unlooper" and reverse engineering it to change a few uart commands.

    Quote Originally Posted by kur4o View Post
    68hc11f1 is 4mhz. I cant find a pic of the crystal used on the board to confirm.
    This got me thinking it would probably advisable to use an arduino with a crystal oscillator, which eliminates my preferred adafruit piece. :-\
    '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???

  13. #178
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    Mask rom code showed some good google results.
    The best invasive method is to scrape the chip and read the data optically.

    I know someone figured an easy way. These D84G TPU processors{I guess some 68hcXX variant} are used in many sir, abs, and other controllers in that era as a primary processor.

  14. #179
    Fuel Injected! vilefly's Avatar
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    Ok. I was extremely busy this week at work, so I did this tonight in the cold after I cannibalized a battery pack to fix my interro scope. Hopefully, this will be enough to keep all coil dwell paranoia at bay, and determine which coils will work best.
    From what I have found out, the LS2 non-finned truck ignition coils (barrel shaped), should work best for this conversion. My '95 wagon has 4.59 mS max dwell and 3.2 mS minimum dwell. According to the Megasquirt coil dwell page, max dwell for the LS2 coil should be set to 4.5 mS. This looks like a perfect match. The LTCC product page says you cannot use the finned LS2 ignition coils. Not sure why.
    "The round body truck coils with the metal fins (19005218) DO NOT WORK"
    Now we also know why the LTCC module has so few parts. It most likely GATES the EST signal to the correct coil in sequence. The lack of other chips is why I suspected this. It just looked too simple for yesteryear's technology. I figured that engineer was clever, and he sure is. More clever than most, since he has a finished product with a minimum of internal parts.

    Anyways, here is my proofs. The battery voltage was 13.85v
    Attachment 12253
    Attachment 12254
    Attachment 12255
    damn it. The server flipped them sideways.
    Last edited by vilefly; 1 Week Ago at 07:20 PM. Reason: crooked pictures

  15. #180
    Fuel Injected! spfautsch's Avatar
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    None of the attachments are working on this end. Anxious to see what you got but no rush. This weekend I'm going to be freezing my stones off finishing my deck rebuild that should have been done in May.

    What I think you might be misunderstanding or in denial about is the notion that multiplexing the EST circuit will work. The reason coil per cylinder setups work well at high RPMs is because they aren't limited to 90 degrees of crank / 45 degrees of distributor rotation to charge. The EST circuit on the other hand has to live within this constraint. What I was trying to illustrate with this post is that if we're multiplexing the EST line, the very best dwell we could possibly get at 6000 RPM, assuming a very tame 30 degrees spark advance is 1.67 ms. That's the opposite of "good".

    edit: I got sidetracked by dogs needing to go outside, but meant to also add that I've been thinking this over non-stop and think there may be hope for the arduino platform. If the original LTCC module multiplexes / gates the EST line (I'd bet you a bottle of good whiskey it doesn't) then what I'm hoping to be able to come up with should be better in the same way sliced bread was an improvement on flour dough baked on a hot stone.
    Last edited by spfautsch; 1 Week Ago at 08:11 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???

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