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Thread: DIY LTCC or similar system for LT1s

  1. #226
    Fuel Injected! spfautsch's Avatar
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    It's hard to put a finger on what all the issues might be, so I can't say positively that noise is one of them but it's highly likely. I unwrapped the right bank upper harness and tapped the 14ga pink wire for power Sunday. In the process I created a small rat's nest of wire that could be contributing also.

    It doesn't help that I'm only getting about 90 minutes a day to work on it, and those are usually distracted minutes. Words cannot describe how anxious I am to get this nailed down and move on to yanking the engine and fixing the oil leak, etc. I'm sure that impatience isn't helping.

    I managed to get an order placed yesterday with digikey for some rc filter parts, a spare boarduino kit and a couple proto boards. Hopefully I'll have that this weekend and can try cleaning up my wiring mess. Between chasing noise / count errors and soforth I've been contemplating how to package the thing for underhood conditions - would love to hear ideas here. Mine is going to be dead simple - potting the whole thing in epoxy. Possibly an external m+f weatherpack connector set for the power, uart and inputs (10 pins total if memory serves) and then either 10 or 16 loose-ended pigtails (8 ttl pins and either two or eight ttl grounds) for the coil igniters coming right out of the epoxy.

    Work's been busy lately so I haven't had much time to research and audit code. Today I was hoping to look for a wiring diagram because the info at http://chevythunder.com/lt1_electrical_page.htm isn't close to what my Y body has - there is no tach wire on my black coil connector.

  2. #227
    Fuel Injected! vilefly's Avatar
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    What I am going to suggest might seem obvious, but it could be a lot of the problem. I suggest twisting the positive and negative voltage supply wires around each other. I remember the early fuel injection computers having issues with their injector drivers until they did that. Twisting the input signal wires around each other is a good idea, too. (5v signal + gnd). Twist all inputs and outputs if nessesary, but start with the heavy current users 1st.
    I was putting together my Rostock MAX 3D printer 3yrs ago, and noticed in the forum that they have feedback issues, so I twisted all my wires in +/- pairs, and never had a problem. So from then on, I twist everything. ABS wheel speed sensors have twisted wires going to them as well, as they are touchy amplified inputs to begin with.

    Worth a shot.

    How about some PCM pinouts?
    95 corvette pinvoltage chart1.jpg95 corvette pinvoltage chart2.jpg95 corvette pinvoltage chart3.jpg95 corvette pinvoltage chart4.jpg
    95 corvette ignition schematic.png
    Last edited by vilefly; 01-09-2018 at 10:33 PM. Reason: more stuff

  3. #228
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    I would have to say potting can have it's downsides, especially with a hard material like epoxy. I have been involved with some items at work that were potted and failures were happening due to the potting and components expanding and contracting with temperature at different rates. Components were breaking and solder joints were getting damaged. Then, it can't be fixed either. Just saying, it's great to seal but can still create problems.

    Now, if you can find a silicone based material that remains soft then you might be better off. Still can't fix it, but at least it avoids mechanical thermal stresses.

  4. #229
    Fuel Injected! vilefly's Avatar
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    I think a light layer with RTV silicone followed with epoxy for the rest of the cavity would balance the need for speed (curing time) and retain some degree of toughness. If it were fast, I'd use 100% RTV silicone, but it would take too long. Silicone dielecric grease would be nice(thermal conductivity), but may leak out before it "dries out" in high temps. A nice "chewy" potting material would be perfect, like the potting material used in Ford TFI ignition modules, and such. Chewy=tough.

  5. #230
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    Have a look at ELASTOSIL products, I have used their two component curing silicone before with great results. I don't remember the exact number, but you mixed it with hardener, poured it into the case like water and it cured chemically, becoming reristant to over 150*C.
    It is a german company, but I'm sure you have something similar in US :)

  6. #231
    Fuel Injected! spfautsch's Avatar
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    All good info, thanks guys. I hadn't given much thought to the possibility of thermo-mechanical stress problems from hard potting. The catalyzed silicone sounds intriguing, but I may go with some combination of silicone around the soldered components and epoxy over that for impact resistance for mine.

    I didn't see any mention of a tach driver in those diagrams, but at least the colors match what I have. For now I'm going to labor under the assumption that the 94-96 Y bodies have a digital gauge cluster. Edit 2: found an addendum to the ltcc install document stating that only a few LT1 cars had the tach driven off the coil - 92-94 y bodies and 93 f bodies. Sweet - sounds like I can eliminate that with conditional compilation for those who don't need it.

    I'm sorry to report I haven't made much progress over the last few days but I did get about an hour on it yesterday during which the outside temp dropped from 62f to 32f finally settling in at a balmy 16f. It's back to "stupid" cold. :-\

    After cleaning up some changes I hadn't debugged fully I was able to get a better picture of what the microcontroller is seeing. This looks likely to be a case of the EST line causing induced or capacitively coupled noise on the low res input. Edit: the test coil was disconnected at this point so the microcontroller was only driving leds.

    Code:
    R1000:S29:D27:C1:E0:L0
    R1000:S29:D27:C4:E1:L0
    R1000:S29:D27:C3:E1:L0
    R1000:S29:D27:C6:E1:L0
    R1000:S29:D27:C5:E1:L0
    R1000:S29:D27:C7:E1:L0
    R1400:S29:D37:C1:E29:L0 << looks like low res rising edge is caught about 29 degrees early here - eerily similar to spark advance
    R600:S0:D16:C8:E59:L0 << low res falling edge is then delayed another 30 degrees
    R1000:S29:D27:C4:E59:L16
    R1000:S29:D27:C3:E0:L0
    If I decide to brave the cold tonight I'll try some external pullup resistors on these inputs since the AVR's built-in pullups are advertised to be in the neighborhood of 20-40K ohms.

    Another possible source of noise may be a ground loop - I added a power ground for the microcontroller to one of the fuel rail bolts but didn't disconnect the other ground at the opti pigtail connector. I'm open to suggestions on what the best practice is here - do I need some type of filter for this secondary signal ground or should I do away with it?

  7. #232
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    LT1 PCMs have separate Tach output, so don't worry about that function.

  8. #233
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    Quote Originally Posted by dzidaV8 View Post
    LT1 PCMs have separate Tach output, so don't worry about that function.
    The flash based LT1 PCMs do, the older chip based LT1 ECMs do not.

  9. #234
    Fuel Injected! vilefly's Avatar
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    Just in case, I would check the alternator output for ac voltage and voltage drops from the positive lead to the alternator connection. Mine had some issues, and I added an extra positive connection to the underhood fusebox when I replaced and upgraded the alternator. Since the optispark runs off of 12V, I figure this could help.

    I tested the optispark with a regulated 5v power supply, and it worked. It was a few months ago, so I hope I am remembering it right. With a clean power supply to it (grounded to the power supply of the controller), it could help eliminate any 12v entanglements.

    I wonder if feedback was designed into the coil drivers like nissans do. One can hook an oscilloscope to a nissan's coil trigger signal and see a 5v representation of the secondary output. Kinda neat, but can cause problems if you are not ready for it. I suggest running your coil trigger outputs through a buffer IC with 8 input/outputs. I think the proper term is "unity gain amplifiers", but they will probably be sold as buffers.

    Probably could use a big, fat capacitor right at the controller for anything else I missed.
    Last edited by vilefly; 01-13-2018 at 12:18 PM.

  10. #235
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by Fast355 View Post
    The flash based LT1 PCMs do, the older chip based LT1 ECMs do not.
    Thanks, that's exactly what I was looking for! Shouldn't be an issue either way, there are plenty of open pins so I'm using the tach driver output to display the state of the EST input when in input test mode.

    Quote Originally Posted by vilefly View Post
    Just in case, I would check the alternator output for ac voltage ... Since the optispark runs off of 12V, I figure this could help.
    I think I've got it sorted out, it wasn't a power problem. I just didn't know where the 12v power to the opti was connected to so I wanted to eliminate any doubt about adequate power. The extra signal ground from the opti pigtail also wasn't the apparent cause of the noise.

    I ended up with 4.7k pullup resistors on the opti pins with a 1000pf cap on the low res input, and a 10k on the EST line. Oddly, 4.7k on the EST line set a "EST Open" code - 41 if memory serves.

    Quote Originally Posted by vilefly View Post
    I suggest running your coil trigger outputs through a buffer IC with 8 input/outputs. I think the proper term is "unity gain amplifiers", but they will probably be sold as buffers.
    I'm opposed to growing part count unless absolutely necessary. When you test, if you can find a need for driving the coils w/ buffers we'll look into it.

    The LS2 coils I have apparently have a very low current requirement on the igniter pin. I'm feeding mine through a 470 ohm resistor in series to the arduino pin. I'm also driving the sequencer leds from the arduino pins directly. I've noticed no issues thus far, but I'll save any further comment for when I've been able to bring the engine up to temp with the system.

    Here's about a minute worth of video demonstrating cylinder #4 driven by the system with the opti running the other 7 cylinders. Once again, apologies for the shoddy camera work. I have no aspirations of becoming a videographer, amateur or otherwise.

    Zip of logs here.

  11. #236
    Fuel Injected! vilefly's Avatar
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    I have to agree to low parts count. Nice video. Got a question. Is your LS1 ignition coil hooked up the the same + lead that feeds the ignition coil? I know the ignition coil feed has a noise capacitor on it right at the coil. Other manufacturers do this too. Try using the V+ feed for the OEM ignition coil and see if your noise goes away. The inductance of he other coil may dampen some noise as well. The ignition module may have other noise-dampening circuits in it (on the shared positive side), such as a zener diode or something. No extra parts required.

  12. #237
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by vilefly View Post
    Is your LS1 ignition coil hooked up the the same + lead that feeds the ignition coil? I know the ignition coil feed has a noise capacitor on it right at the coil.
    Yes, and I'm relatively sure there's nothing like that on my '95. Last weekend I stripped the tape off the entire right side harness from the #8 injector to where the MAF sensor branches out including all of the ignition feeds and there's nothing but wires and connectors.

    If I can find all my old spark plug wires I'll try firing it with the original ignition system disconnected tonight. Fingers crossed, bunghole clenched...

  13. #238
    Fuel Injected! spfautsch's Avatar
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    As my videography skills run, I accidentally deleted the crank / start segment from my phone. It was unimpressive because I'd already started it twice before - once so I wouldn't drop my phone in the event the engine came apart and I soiled myself, and the second time my wife was "helping" with the video. The valves had warmed up by #3 so it was a bit of a long crank as I suspect it flooded slightly. After the final video when ECT was around 60c I re-started it and it fired off just as vigorously as we're all used to.

    At any rate, proof of concept at long last. Also, revel in my woodworking skillz (temporary coil brackets).

    Short clip revving (haven't looked at the logs to see peak rpm).

    90 second clip showing eehack when it switched to closed loop. At the end I walk around and pick up the disconnected ICM and coil connectors as well as the opti coil wire.

    Logs


    After disconnecting the ICM plug, DTC 41 set immediately as it did when I was using a 4.7k pullup. So I suppose I might need to try a zener diode or something on this pin to keep the ECM from freaking out.

    I'm stoked to have gotten this far. There's still a lot of work, but that's all going to be dead nuts fun for me.

    What still remains to be seen is what the Atmega will behave like the first time I get stuck in St. Louis traffic on a 95F day.

    I'm going wander over to my neighbor's place, have a couple glasses of bourbon and come home and sleep like I haven't in a few months. I'll do some research tomorrow and try to decide how to publish the source code.

  14. #239
    Fuel Injected! vilefly's Avatar
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    Very awesome work! I commend you on beating me to the punch very soundly. I especially like the wooden coil bracket, seeing how most bracket kits cost $85 and up.
    You are using the mega2560 unit, right? I imagine you can send a password-locked zip file. If legality issues concern you, you can draw up a patent-style Disclosure Document that proves you thought of the idea before you disclosed it to someone else, and have them sign it, and send it back to you. This will hold up in a court of law, but am not sure if you need to have it notarized. Should provide you with some code protection at least.

    What I don't know, is how you can download what has been flashed to the AtMega so you can prove the code was stolen with a comparison. Should probably keep that secret to yourself, though. Just say if you can do it or not.

    As to the code 41- I think the circuit impedence on the EST line is 10k ohms. Perhaps a 10k resistor in between the arduino and the EST white wire might fix it. (ignition module terminal "B")
    95 corvette optispark.png

  15. #240
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by vilefly View Post
    Very awesome work!
    Thx!

    Quote Originally Posted by vilefly View Post
    I commend you on beating me to the punch very soundly.
    I wasn't exactly trying to scoop you - just possibly a little more enthusiastic about the prospect of <the title of the thread>. DIY is ingrained in me fairly deeply.

    Quote Originally Posted by vilefly View Post
    You are using the mega2560 unit, right?
    No, 328P. 28 pin dip package. Google "DC Boarduino Kit". Us hillbillies with shaky soldering hands love 'em. I'll have to read the 2560 datasheet to see what changes would be needed to make my sketch compatible (if possible).

    Quote Originally Posted by vilefly View Post
    I imagine you can send a password-locked zip file. If legality issues concern you, you can draw up a patent-style Disclosure Document ...
    My legal concerns aren't focused on you or the gearhead community at large, but the inventor of the namesake device. I just want to protect myself from legal repercussions if Bailey owns a patent and decides to go after me. The only reason I put all this work in is to have the source open and available for everyone to modify and improve upon.

    Quote Originally Posted by vilefly View Post
    What I don't know, is how you can download what has been flashed to the AtMega...
    The compiled binary can be flashed with avrdude if you can wrangle the command line. But I don't intend to make it that difficult.

    Quote Originally Posted by vilefly View Post
    As to the code 41- I think the circuit impedence on the EST line is 10k ohms. Perhaps a 10k resistor in between the arduino and the EST white wire might fix it. (ignition module terminal "B")
    I'm relatively sure the "EST Open" refers to not having enough loading on the EST circuit (i.e. the absence of the ignition control module). So adding resistance is probably going in the wrong direction. In the grand scheme of things this is the proverbial gnat on an elephant's ass.

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