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Thread: DIY LTCC or similar system for LT1s

  1. #466
    Fuel Injected! spfautsch's Avatar
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    If you haven't assembled the PCB you're probably fine. Desoldering the RC network resistors on the coil outputs was kind of a pain. I lifted several of the pads but luckily none that required traces to be repaired. If I had a soldering iron that wasn't made by fischer-price I might have been able to do better.

    The coil indicator LEDs are probably not a dangerous amount of load for the AVR if you're using the same coils I am. More details on the coils later.

    I'm posting my math for everyone to double check, please don't hesitate to do so and post any corrections.

    Voltage drop over the 1k ohm current limiting resistor driving the red LED indicating the spare output (I configured it for a tach driver) measured about 3.2 average - peak of 3.6 at turn-on. Sticking with average that's 3.2 / 1000 = 0.0032 A or 3.2 ma. If my math is correct there's no worries here. With that said I'd still eliminate / omit the coil indicators - they were really only intended for experimental / diagnostic purposes. If anyone thinks they'll prove useful I can split their grounding network on a re-designed pcb so they can be configured with a removable or soldered jumper.

    Moving on to the coil igniter circuits, I replaced the 470 ohm resistors with 100s. Previous testing showed 0.425ma draw. Getting a clean sync on the signal was difficult but I was able to get a faint image about every other engine revolution. Across the 100 ohm resistor I was seeing 60 millivolts. This waveform had a surge at the beginning then settled down to a flat voltage level - the peak was probably 80mv but I'm going to use 60mv. So 0.06 / 100 = 0.0006 A or 0.6 ma. This is well within the capabilities of the AVR even with coil indicator LEDs and still leaving headroom for other loads.

    I am somewhat baffled by this current figure. The reason I decided to research this topic further is because I was afraid the coil igniters weren't getting driven into saturation and spark energy was suffering as a result. Unfortunately this critical piece of data doesn't appear readily available on the interwebs. What would really be useful here are some standardized specification data. Search as I might, I've found nothing similar to a datasheet on any of the GM CNP ignition packs. All I have to work with are anecdotal reports.

    My primary source of data was the oft-mentioned megaquirt 2 sequencer manual [link]. In all references to the igniter circuit draw, "a few dozen milliamps" is given. Also salient is the mention of 1000 ohms in series (internal to the sequencer) with the output circuits being used to drive the igniters.

    Another tidbit I found in the beginning and then re-discovered a few days ago is [this] post on allaboutcircuits.com's discussion forum by a college student struggling with a very similar project for his 99 Infiniti. Seems like he had problems with connected and / or induced interference. But the recurring theme seemed to be 20ma at TTL levels on the igniter pin.

    So, barring someone coming forward with veritable treasure trove of technical data on coil packs, I suppose what's needed is independent testing not only for igniter current but ignition energy relative to dwell time.

    Based solely on appearance, I purchased 8 coils off eBay for a very reasonable price that I believed to be these LS2 "hot" car coils.



    GM PN: 12573190
    AC Delco: D514A

    But I found just a few days ago they are in fact these.



    GM PN: 12658183
    AC Delco: 12674754

    Based on application data it seems like the coils I have might be a considerably newer design than the 4ms "hot" coils. But the current draw on the igniter input indicates they're anything but similar to the 12573190 coils if the anecdotal data mentioned previously is accurate (20 to several dozen milliamps). This is a huge difference indicating the coils I have utilize a shielded FET igniter instead of a more standard IGBT.

    I've found a source for some of the D514A coils on A website for about $20 apiece so I'm seriously contemplating buying a set. Also logical would be testing the "legacy" LS1 coils with the exposed laminated core.

    For those of you planning to install the test setups I'd recommend you pull the brakes if you've already chosen a coil pack, as I'd really like to test the controller driving at least one of each of the variants, especially these beasts.



    GM PN: 190005218
    AC Delco: D585

    So barring any volunteers willing to loan me hardware I guess I'm going to build a test platform and start collecting parts.

    I was able to drive it some today and it was better, but not absolutely impressive as back in May. I'll try to post more info relevant to drive data in the "humidity" thread [link], but it may be several days.

  2. #467
    Fuel Injected! vilefly's Avatar
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    Started testing my coils (12559693) to find the best dwell time. Ran into a snag. My radio shack logic pulser got killed triggering the coils. It is rated for 200mA max, and was overloaded by the trigger circuit. The circuit when loaded, showed a distorted waveform being dragged down halfway to the 0V line. Didn't get a chance to measure the current draw before the logic pulser died. Does not act like an IGBT or a MOSFET at all. Pretty thirsty for a transistor, I'd say. My next trigger source will be backed by a 5V 1A regulator.

    Ran out of time today. Will try again tomorrow. Too much crap to do.

  3. #468
    Fuel Injected! spfautsch's Avatar
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    Hey all I wanted to drop in an update on the project status.

    As many of you have probably seen over in the 'humidity' thread I've found what I believe to be the sole cause of my driveability problems - a slipped opti hub. My priority at the moment is to get this fixed so a determination can be made as to whether this was everything that was wrong, or just one piece of a larger puzzle.

    In the mean time, for anyone still wanting to actively test I'd like to hear your coil PNs so I can prioritize which to purchase for testing. It may be several weeks before I have the funds available to buy test units, and at the moment vilefly is also extremely busy. So unless anyone would want to volunteer to tackle this, all I can offer is hopefully soon one of us will be able to determine specs on the coils mentioned in post #466.

    If any of these coils that have been reported to draw several milliamps on the igniter pin will work in the current PCB configuration, it will definitely require replacing all the rc network resistors on the coil driver circuits with 47 or 100 ohm pieces. And in the case of the coils vilefly owns it's seems likely that a separate driver stage will be required.

    It was a monumental oversight on my part to have assumed all these coils would have similar igniter circuit requirements. For this I can only apologize. If any of the paying testers would like to abort at this point I'll gladly buy your kits back or refund your $25.

    The only good news I have to report is that the 12658183 coils I happened by dumb luck to choose will work with no problems whatsoever. I'm anxious to test one to determine dwell requirements.

  4. #469
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    https://www.eevblog.com/forum/projec...il-driver-cct/

    Some interesting reading.

    I will try to gather a list of all available coils through the years and link them to pcm they were used with.

    I also remembered that there were a dwell tables in some of the ls calibrations.
    There is 1 main table base dwell time vs rpm vs voltage.
    There is coolant temp correction multiplier vs voltage, and map correction multiplier.

    So to dublicate the tables you need 4 inputs: map, coolant, rpm and IGN voltage.

    I will get you some screenshots of the tables later for reference

  5. #470
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    SOme coil reference by years.

    The one you have are not available in the catalog, I could only find that they interchange with 12621750. So you got one of newest designs. I will try to dig out a 2014 truck bin to see the dwell tables.

    The general consensus is that d585 is the highest output coil, so if you`re shopping look for that one.
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    Last edited by kur4o; 1 Week Ago at 03:45 PM. Reason: Added high res image

  6. #471
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    http://www.gearhead-efi.com/Fuel-Inj...7&d=1529720855

    A printout of 2015 truck calibration data. Search for dwell.

    I hope the coils you have are the same used with this 2015 truck.

  7. #472
    Fuel Injected! vilefly's Avatar
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    Looks like base dwell @ 14v ranges from 3.10 mS to 2.41@8000rpm.

  8. #473
    Fuel Injected! spfautsch's Avatar
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    Good info kur4o, thanks!

    Quote Originally Posted by kur4o View Post
    I think I ran across this in some of my initial research and dismissed it as a nothing sandwich. There's no meat between the bread, just anecdotal nonsense that couln't be verified. I've never found anything leading me to believe the early LS (or even the current stuff) had feedback capable coils. If that's the case it opens the doors to a lot of possibilities for future work.

    Quote Originally Posted by kur4o View Post
    The general consensus is that d585 is the highest output coil, so if you`re shopping look for that one.
    They're also the most expensive. I had one saved in my Amazon cart at a relatively decent price, but it was no longer available this morning. :-\ I'm still paying for the recently acquired valvetrain parts - in more ways than one. My wife has been threatening to "roll <censored: the car> out in the driveway and set it on fire".

    From what I've been able to gather from RockAuto's parts lookup the 12658183 coils I have were only used on some of the 2014 and newer LT1,LT4 and LT5s and only in the Y-bodies. I've also been unable to find an abbreviated Delco part # (i.e. D514).

    Edit: correction - it looks like these were also used on the 6.2 truck engines starting in 2014.

    Edit2: Interesting - AutoZone is describing the AC 12674754 a "Capacitive Discharge System".

    Quote Originally Posted by vilefly View Post
    Looks like base dwell @ 14v ranges from 3.10 mS to 2.41@8000rpm.
    I wonder why they're reducing dwell with RPM. It seems like if there is time available to get a fatter spark, why not utilize it? Obviously above 5000 RPM the driver is requesting all the "go" the machine has available.

  9. #474
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    In 2014 Gm introduced new Pcm with the Direct injection v8s. The ingition drivers might also get an upgrade and the need of new coils. I saw some interesting tables labelled multi pulse spark dwell. Not clear what they do and is this coil capable of multi spark events. They have the shortest dwell of all of the GM coils. When you factor the 10% coolant reduction you land at 2.16ms dwell at 8000rpm.

  10. #475
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    Some more dwell food to digest, while contemplating on a new fire extinguisher system.
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  11. #476
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by kur4o View Post
    I saw some interesting tables labelled multi pulse spark dwell. Not clear what they do
    Don't they all appear to be zeroed? Makes me wonder if there were different calibrations for the vehicles equipped with the round coils. All the parts lookups seem to specify "With round shaped coils OEM #12674754. For 1st design see 12619161. Service coils marked Delphi"

    Quote Originally Posted by kur4o View Post
    They have the shortest dwell of all of the GM coils. When you factor the 10% coolant reduction you land at 2.16ms dwell at 8000rpm.
    This makes me wonder if the coils are smart enough to use the dwell duration as a signal to determine how many discharge pulses to fire. Now I'm anxious to test them and see what the high tension side is doing.

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