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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; 09-10-2019 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.

  12. #477
    Fuel Injected! spfautsch's Avatar
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    I wanted to drop in an update - unfortunately nothing has happened at my camp along the lines of testing coils. When I replenish my toy budget I promise I'll get on it, but it could be a while.

    I know it will taste like weak tea to those who already own or have purchased coils, but I feel completely confident the GM 12658183 coils I have will work perfectly with whatever RC network resistors you have in your version 1.0 boards.

    The driveability problems I was experiencing over in the humidity thread seem to have been caused entirely by the hub slipping 30+ degrees retarded in my opti. After fixing this I got it running last saturday, just in time to be pressed in to service as my daily driver since the Jetta has a siezed brake caliper. I just filled up the test mule after putting another 513 miles on it while working through a tuning workshop headed by none other than kur4o, and despite the ridiculously rich smell it's emitting I had to double-take when the gas pump popped off at 17.48 gallons and then I gave it another five or six squeezes just because I didn't believe it. I was by no means driving in a manner conducive to low fuel consumption, and experienced zero driveability problems that couldn't be attributed to the ASR or the fuel pump swallowing air after pinning it's ears back in 2nd gear with good traction and 1/4 tank of fuel. This was with 4.5ms dwell, but I suspect these coils would run just as well in the neighborhood of 3.5ms.

    Food for thought...

  13. #478
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    29 MPG, holy hell! Back when my Integra actually ran properly that's about what I got in it cruising around for work. If I can get the Corvette to do that, I'd be thrilled!

    As for the coil selection, I was going for one I found a deal for. I still haven't had the budget to jump on them yet (as expected; the not-an-LT1 race car got priority since we have a race coming up in the middle of October), but they're too good a deal to pass up. According to the ad they're 12658183 as you mention above, but...well, we'll see about that. I won't trust it until I have them in my hands. That being said, if they really are that part number, then I'll be totally stoked. If all goes well I'll be able to order a set in one week!

    Of course, that would mean the race car has no more surprise maintenance. I'll let you know.

  14. #479
    Fuel Injected! spfautsch's Avatar
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    I'm still not sure I believe it. My CCM went goofy last night (during an E-side flash no less) and I had to unhook the battery to make it quit popping my hatch. This means the trip odometer got lost from when I filled up Tuesday morning. The 513.7 miles was me re-tracing my driving via google maps. But at the very least I drove 120 miles a day for 4 days without any side trips (of which there were many), which falls in the neighborhood of 27mpg. I really need to strip my interior and find what wires are dicked up in the console that are causing the CCM to go batshit crazy.

    Good luck with the coils you're looking at - I'm sure if they have the GM logo molded in the cases they'll work just fine.

  15. #480
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    In an effort to fine tune the controller I will try to hack the GMs ignition controller used on numerous, different PCMs.

    The ignition controller is found on v6 fwd pcms,early ls1 pcms and 512kb and 1mb ls1 pcms.
    It is labeled 11124 a delco chip part number and is a 52 pin QFP package.
    It can run at least 8 individual coils, and get a signal from multiple cam/crank sensor.

    All coil outputs goes through 431 ohm resistor[1mb pcms have different resistor, and the value have not been confirmed yet] and have a capacitor wired for noise reduction. The cam/crank inputs goes through a 471 ohm resistor and a capacitor. there are a 4mhz ceramic resonator wired on 2 pins of the chip, and we can assume it runs at 5v, since all gm pcm voltage regulators and in general the ICs can run at either 5v or 3.3v.

    It should output the cam/crank signal to the main CPU. So it can be some sort of filter too. It must sense open inputs, shorts to ground and B+ and sends the info to the CPU.

    It can be configured by the cpu to run in different modes. Single coil output with a distributor, single coil output with external ICM, and multi coil setup for ls1 and northstar type of coils and for 4,6 or 8 cylinders setup.

    SInce it get the signals for crank/cam it should also be able to fire the coils on it`s own based on the input signals. A possible use of this will be at startup and limp home mode.

    The ultimate hack will be to make it accept an LT1 opti signals.

    The output resistors can be some kind of current limiting device, so the chip doesn`t get fried by the coils` ignition driver.

    The coils could also have some smart ignition driver that can auto trigger the coils and prevent melt down. Someone with a fried coil can try to open the case and see what is inside.


    I will look more on the hardware side to map mostof the pins.

    ANd some random pics of the chip, The blue part near the chip is the ceramic resonator.
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