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Thread: DIY LTCC or similar system for LT1s

  1. #496
    Fuel Injected! spfautsch's Avatar
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    I guess I misunderstood what you were getting at with the rpm spark advance adder. It seems a little like you're trying to fix a problem before you know it exists. Take it from someone who's done that quite a bit lately - science is your friend.

    Whatever the case, since we made the firmware and can modify it to our liking, the first, most obvious place to start trying to fix deficiencies is in the controller firmware, not the PCM. This was the first "commandment" I adopted when I decided to give this a shot - no tuning changes should be necessary. Even if only to avoid a CEL that's easily disabled - a problem that was fixed by finding the right set of resistors (thanks be to vilefly). If users disagree with this and want to take my code and fork it in a different direction you have my blessing and encouragement, just call it something else and keep your sources publicly available.

    So, I'm hoping to reel you back in on how the spark fire event happens - there's nothing going on in the controller firmware other than the code I posted in the disassembly. This is the highest priority interrupt on the AVR so when the PCM drives the EST line low within four clock ticks all other code execution is pushed down the stack and the ISR that fires the controller's coil is executed. To quantify exactly how much delay that is would require stepping through the disassembly and figuring out how many clock cycles the instructions eat, then dividing by 16mhz. In summary - it doesn't matter how fast the engine is spinning, when the PCM commands the EST line low the AVR stops what it's doing and handles the coil firing.

    Edit: going by the instruction set summary it looks like this comes out to a maximum of 14 clock ticks for BTDC spark timing. Adding the worst case of 4 before the ISR begins executing that looks to be 1.125 microseconds (0.000001125s). Check my math, but at 8000 rpm doesn't each crankshaft degree represent about 20.8 microseconds? If that's correct the coil firing delay introduced by the controller would be about 0.054 degrees? So if there is any delta it should be too small to observe at any engine speed the PCM is capable of.

    I mean this in a positive and joking way, but I think you might have an addiction to patching. If you're jonesing for a new challenge there's somebody over here asking for a lean cruise strategy for $ee. This would interest me immensely but it's not something I'm capable of and wouldn't have time to test until spring of 2020. It seems to be right in your wheelhouse.

    In case anyone's interested, my personal roadmap / goals as they pertain to this project are:

    1) replace my wideband and control power to it so it's not being heated without the engine running - should get this done this weekend

    In no particular order other than how they're popping out of memory:

    *) get my tune to a solid, consistent baseline so I can work on improving and optimizing the diy-ltcc firmware without having to second-guess the cause of any problem - pretty sure this is done but would like to verify with reliable wideband data
    *) gather igniter current and target dwell data on some of the most common coils that will be used here
    *) improve and optimize the firmware as mentioned, including possibly adding misfire detection, verifying dwell times, etc.
    *) add an in-circuit programming header and jumpered ground planes for the leds, and order another, larger batch of boards
    *) build an arduino based injector flow bench - I know, this has nothing to do with the project - just a pipe dream I wanted to share

  2. #497
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    Since the LTCC fires immediately after it gets low on ESC line, there shouldn`t be any spark advance error. The ICM module should also have some delay so if these 2 match, we will have dead spot on spark advance.
    The only problem that may arise will be that dwell time is not optimal when the fire event is executed. You can shed some more light on that part.
    At 7200rpm which is the built in opti software limit, 1 degree rotation will be done in 0.023ms.


    I looked at the dwell code the pcm use. There is some built in limit which is opti signal - 0.60936ms. So I guess the coil needs at least 0.60936ms off time or it could be some lag compensation. A dwell adder when engine is cranking is at 0.437ms and the dwell is calculated different above 3400 rpm[some extra calculations are done].
    Last edited by kur4o; 1 Week Ago at 09:40 AM.

  3. #498
    Fuel Injected! spfautsch's Avatar
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    I believe I read somewhere there is also a small delay for the coils - the magnetic field doesn't collapse at the same rate after power is cut to the primary winding depending on the size of the core and winding specifics, etc.

    I'm really not terribly concerned with how the $ee PCM manages dwell because it's designed to work within the constraints of a single coil and distributor. There may be things to learn from it but I'd be more interested in what the newer coil per cylinder tunes do. I have yet to really dig into this subject other than skimming over (and being largely confused by) the dwell table for the tune you posted that uses the 8183 coils I have.

    The dwell time is really the thing I want to research, test and improve upon. The way the dwell logic works is based on degrees - the lookup table is the target dwell time converted to crankshaft degrees vs engine speed. There is a voltage compensation table applied also that is somewhat generic and should probably be customized based on test data for different coils. Lastly there is a map adder that adds a fixed amount of dwell for large drops in map - sort of a "pump shot" type adder with a timer. Ultimately I think I want to change this to a map adder table which would give more predictable, linear results.

    The dwell lookup routine finds the desired degrees of dwell for engine speed, voltage and map and then adds current spark advance to this to return the degree count where dwell should begin. It also has an overflow function for instances when dwell needs to start before the previous cylinder (or two, three cylinders) has reached TDC. If you enable logging and look at the data you'll see dwell specified as:

    Code:
    R906:A29:D0.61:C1:M458:V13.61:T30:E0:L0:S0
    R901:A29:D0.62:C8:M520:V13.65:T31:E0:L0:S0
    R900:A27:D0.62:C4:M585:V13.59:T32:E0:L0:S0
    R910:A26:D0.60:C3:M678:V13.66:T33:E0:L0:S0 < dwell begins at 60* BTDC
    R923:A23:D0.58:C6:M794:V13.66:T34:E0:L0:S0
    R1055:A12:D0.45:C4:M930:V13.45:T40:E0:L0:S0
    R2153:A24:D1.4:C4:M934:V13.52:T40:E0:L0:S0
    R2772:A29:D1.38:C4:M153:V12.95:T40:E0:L0:S0 < dwell begins at 128* BTDC
    R2402:A29:D1.23:C4:M112:V13.12:T40:E0:L0:S0
    R1984:A27:D1.4:C4:M157:V13.33:T40:E0:L0:S0
    R1636:A27:D0.80:C4:M205:V13.42:T40:E0:L0:S0
    R1326:A27:D0.67:C4:M268:V13.44:T40:E0:L0:S0
    R1099:A27:D0.69:C4:M337:V13.61:T40:E0:L0:S0
    Note that this data is filtered through a conversion script so you'll see raw timer #s for RPM and raw adc counts for voltage.

    I've been thinking about how to switch to time based dwell after sequence has been detected, but there are bunch of pitfalls that I'm not sure how to work around. Particularly the part where dwell needs to begin one or more low-res / TDC signals before the firing cylinder is on it's compression stroke.

  4. #499
    Fuel Injected! spfautsch's Avatar
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    As I've been re-routing wiring through my interior today and had to remove / clean out a bunch of junk to add a power relay for my wideband so it's turned on by the ignition controller after ~300 engine revolutions, I ran across a couple blown fuses and thought it would be a good idea to drop a reminder here - anyone planning to test should upgrade your coil fuse from 10 amps to 15-20. Mine is currently 25 because the same circuit is powering my wideband and a USB hub connected to the ALDL and DIY-LTCC serial ports. Carry some spares because if you get into the 6500 rpm range you may find out quite abruptly what happens when you have more than four coils dwelling at the same time.

  5. #500
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    I suggest a b+ coil feed wire upgrade with the LTCC.
    The factory wiring of the coils have 2 separate circuits bank to bank each running 15amp fuse with 0.8 wires. That will be the minimum and going to 1 wire is preffered to overcome any voltage drops at high rpm.
    I think the ltcc needs to sample voltage on that wire too.

    How about the spark plug gap. Ls1`s use 0.06'' vs 0.05'' on stock lt1. Did you adjust yours`.

    On a side note how hard will be to repurpose the LTCC controller to signal translator from opti to ls1 based 24x signal. It might get very popular compared to 1200$+ commercial products.

    I will dig into ls1 disassembly and try to find anything dwell related. I don`t expect any major changes through out the years.
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    Last edited by kur4o; 6 Days Ago at 05:19 AM.

  6. #501
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by kur4o View Post
    The factory wiring of the coils have 2 separate circuits bank to bank each running 15amp fuse
    I would assume those fuses are probably well oversized for the D580 coil requirements. Of course, I only know what my 8183 coils draw by way of having blown fuses.

    The fuses I blew were the original 10 amp that I killed intentionally, and then a 15 amp that only got taken out because I accidentally disconnected the EST wire from the breadboard and all the coils dwelled simultaneously without firing. Before I added my wideband to this circuit I took it to 6500+ rpm several times with a 15 amp.

    I cut my original coil power circuit back by several feet and used heavier wire between the two banks of the new harness. The controller should be powered by this circuit so it's measuring voltage as close to the coil power as possible. The total power draw of the controller is going to be less than 0.2 amps so not much to worry about there.

    Quote Originally Posted by kur4o View Post
    Ls1`s use 0.06''
    Interesting, I'm seeing one part lookup source calling for AC 41162 iridium gapped at 0.040" as the OE plugs for the first gen LS1.

    Honestly, I don't think gap makes much difference. I'm currently running double iridiums gapped at .045. I have some cheap copper plugs I could gap at .055 or .060 but it's a pain to get the boots to click on 6 & 8 because of the headers and the dipstick tube so I'm going to probably pass on experimenting with different plugs.

    Quote Originally Posted by kur4o View Post
    On a side note how hard will be to repurpose the LTCC controller to signal translator from opti to ls1 based 24x signal.
    We discussed that starting around page 28 of this thread. [link] My opinion really hasn't changed much about it but it would be fairly trivial to attempt if I was in the right mood. I just don't see a really compelling reason to want to try.

  7. #502
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    Quote Originally Posted by spfautsch View Post
    I would assume those fuses are probably well oversized for the D580 coil requirements. Of course, I only know what my 8183 coils draw by way of having blown fuses.

    The fuses I blew were the original 10 amp that I killed intentionally, and then a 15 amp that only got taken out because I accidentally disconnected the EST wire from the breadboard and all the coils dwelled simultaneously without firing. Before I added my wideband to this circuit I took it to 6500+ rpm several times with a 15 amp.

    I cut my original coil power circuit back by several feet and used heavier wire between the two banks of the new harness. The controller should be powered by this circuit so it's measuring voltage as close to the coil power as possible. The total power draw of the controller is going to be less than 0.2 amps so not much to worry about there.



    Interesting, I'm seeing one part lookup source calling for AC 41162 iridium gapped at 0.040" as the OE plugs for the first gen LS1.

    Honestly, I don't think gap makes much difference. I'm currently running double iridiums gapped at .045. I have some cheap copper plugs I could gap at .055 or .060 but it's a pain to get the boots to click on 6 & 8 because of the headers and the dipstick tube so I'm going to probably pass on experimenting with different plugs.



    We discussed that starting around page 28 of this thread. [link] My opinion really hasn't changed much about it but it would be fairly trivial to attempt if I was in the right mood. I just don't see a really compelling reason to want to try.
    When I had the stock ignition system in my Vortec 350 I ran an AC Delco platinum that was gapped at 0.035" per a GM TSB. When I swapped to the Davis Unified Ignition setup I ran NGK 7164s gapped at 0.050". Saw some small torque gains across the whole RPM range. When I switched to the D585 coils gained about 15 ft/lbs across most of the powerband. If you have a hot ignition setup, especially coil near plug I recomeend a fine wire iridium plug with a 0.050" gap. The NGKs worked great and are under $6 a plug. if you have the plugs out anyway, get an index washer set and index them with the gap toward the intake valve.
    Last edited by Fast355; 6 Days Ago at 11:52 AM.

  8. #503
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    Injectors are also wired on the 15amp fuses. The thirstier coils are the d585. Gm doesn`t recommend changing the gap on iridiums on ls1 engines. I am not sure but they are set at 0.040'' and must not be changed. It could be something specific to iridium conducting electricity.
    So if the spark plug gap is defined by the coil used, I can recommend 0.060'' gap on platinum and copper and 0.04'' on iridiums.

    And yes gap can make a big difference on performance. It changes both the intensity and duration of the spark.

    We discussed that starting around page 28 of this thread. [link]
    I really need to reread the whole thread. I lost track of most of the stuff discussed long time ago. Even the same pic was uploaded there. I scored it from a totally different source.
    Last edited by kur4o; 4 Days Ago at 02:58 PM.

  9. #504
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    LS1's started at 0.060" and then GM released a service bulletin to drop the gap to 0.040" because of misfire complaints once the engines got some miles on them.

  10. #505
    Fuel Injected! spfautsch's Avatar
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    That seems to make sense of the conflicting info I was seeing on the big box parts website - some were 0.060 and the ACDelco "OE" parts were gapped at 0.040. So even GM's guys got it wrong out of the gate.

    Just wanted to throw out another small update - I got an email from the place that made the first batch of circuit boards saying they're doing a 20% off sale until the end of December. So I'm simultaneously working on adding the ICP header and LED jumper circuits to the original 1.0 PCB design, and I also ordered a D580 and D581 coil and should have them in a few days. Once I'm sure the circuit will drive all the coils I have, I'm planning to order a fairly substantial quantity. If nothing else, I'll have a bunch of really cool bookmarks. :-)

  11. #506
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    Quote Originally Posted by spfautsch View Post
    That seems to make sense of the conflicting info I was seeing on the big box parts website - some were 0.060 and the ACDelco "OE" parts were gapped at 0.040. So even GM's guys got it wrong out of the gate.

    Just wanted to throw out another small update - I got an email from the place that made the first batch of circuit boards saying they're doing a 20% off sale until the end of December. So I'm simultaneously working on adding the ICP header and LED jumper circuits to the original 1.0 PCB design, and I also ordered a D580 and D581 coil and should have them in a few days. Once I'm sure the circuit will drive all the coils I have, I'm planning to order a fairly substantial quantity. If nothing else, I'll have a bunch of really cool bookmarks. :-)
    Bwahaha. I see we both made the same "mistake" on our 1.0 designs...leaving out the ICP header. "It's fine, I can just reprogram it with a pogo adapter! ...oh wait"

    Cool stuff, best of luck with the 2.0!

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