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Thread: DIY LTCC or similar system for LT1s

  1. #271
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    I see your point with the DIY-friendly side of Arduino, and probably can agree. You are also right not to make this topic a discussion about pros and cons of different IDEs, so I won't. I just couldn't have helped myself to make that point. :)
    I'll work on your code to move more work on precompiler and clean up the lookups when I'll find some spare time.

  2. #272
    Fuel Injected! spfautsch's Avatar
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    Just so I'm understanding, you're saying you can build precompiler directives that will perform the function of the populate routines so users can edit the following macro definitions / constants and end up with a custom dwell table?

    Code:
    #define DWELL_TGT 4.5       // dwell target in milliseconds - edit to your liking (using 4.5ms for standard ls2 coils)
    #define CRANK_DWELL_TGT 3.2 // dwell target for cranking / startup
    
    #define VOLT_COMP_8 2.4     // adds / subtracts from dwell target at given input voltage
    #define VOLT_COMP_9 1.5
    #define VOLT_COMP_10 0.9
    #define VOLT_COMP_11 0.4
    #define VOLT_COMP_13 -0.2
    #define VOLT_COMP_14 -0.4
    #define VOLT_COMP_15 -0.7
    #define VOLT_COMP_16 -0.9
    #define VOLT_COMP_17 -1.0
    Or are you talking about making the tables statically initialized variables like the RPM table?

    Code:
    int rpmReference[RPM_DIVS] = { 25, 50, 75, 100, 125, 150, 175, 200, // the rpm reference
      400, 600, 800, 1000, 1200, 1400, 1600, 1800, 2000, 2200, 2400, 2600, 2800, 
      3000, 3200, 3400, 3600, 3800, 4000, 4400, 4800, 5200, 5600, 6000, 6400, 6800 };
    Also, I'm always a proponent of optimizing code but flash and memory resources aren't in short supply at this point.

    Code:
    Sketch uses 9816 bytes (31%) of program storage space. Maximum is 30720 bytes.
    Global variables use 1013 bytes (49%) of dynamic memory, leaving 1035 bytes for local variables. Maximum is 2048 bytes.
    Lastly, I don't see a point in trying to run this on a lesser mcu. This isn't a project focused on profitability, so saving a dollar or two on the mcu only to limit what can be added in the future seems counter productive. One of the reasons I developed a fondness for the adafruit clones is because they developed a bootloader mod that allows no-wait program startup while maintaining the ability to flash the chip over uart hands-off. This is important - I want the user to be able to update the firmware easily in the same way they can tune flash based PCMs. I also want it to be easily customizable, even if that means something as trivial as the end user printing their name or VIN # to uart on startup.

    Latest changes tested and uploaded. Link to github repo is in my signature.

  3. #273
    Fuel Injected! spfautsch's Avatar
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    Partial schematic interfacing to an Arduino compatible device. Sorry for the bunching on the input side, I'm still learning how to use this drawing soft.

    Wire colors on the input side are only confirmed on the Y chassis code. Others may use different colors.

    diy-ltcc-boarduino-1.0-partial.jpg

    The LED + limiting resistor on pin 13 are usually present on all Arduino-like devices so I didn't number them. My ultimate goal is to develop a complete schematic and turn that into a single plane PCB with the Atmega (28 pin dip) directly onboard instead of using the Arduino device as a "daughter board". If that works out maybe we can arrange a group buy for a large quantity.

    I'm hoping it's obvious, but just to be safe the the ancillary output circuitry on pin 4 (coil #1) needs to be duplicated for the other 7 cylinders.

    Edit: R3 and R4 (the famous impedance matching network) is an approximation of potentiometer measurements from this post that produced ~4.29 volts on the EST line's diagnostic ADC channel. Testing and possible fine-tuning may be required (I can't find a 5.6k resistor in my substantial collection of "stuff").


  4. #274
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by kur4o View Post
    The last stable version is 4.7. I am working on some version labeled 4.9 but is far from ready. Anyway my improvement will be only on added mode 4 controls and some clean up of the patches.
    Thanks for the explanation. I'd seen mention of 4.9 in your patches thread and wasn't sure what was going on.

    Quick question for you or anyone that might know - I'm relatively sure there aren't any calibrations that call for it, but is it possible for the PCM to command negative (atdc) spark timing? I'm thinking about how to implement some self-diagnostics, and wondered if atdc timing was a possibility for the EST signal.

    Lastly wanted to update that I started it four times today, the first round the ECT was at 10c / 50f and it fired right off as did the three subsequent times. I think my longer cranking times were mostly a side effect of my battery getting ready to roll over dead on me. I did have a particularly long crank last night that I'm sure wasn't imagined, but I probably caused that when I yanked the injector fuses to simulate a stall. Ambient was also easily 6c / 10f colder.

  5. #275
    Fuel Injected! vilefly's Avatar
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    Quote Originally Posted by spfautsch View Post
    Quick question for you or anyone that might know - I'm relatively sure there aren't any calibrations that call for it, but is it possible for the PCM to command negative (atdc) spark timing? I'm thinking about how to implement some self-diagnostics, and wondered if atdc timing was a possibility for the EST signal.
    I think when the ABS is triggered, the ignition timing could be retarded that far, but I have no proof. Would have to scope/datalog during an ABS stop. If it were a chrysler, it would happen between shifts, but not in the case of a 90s chevy.
    Interesting question. Did you have some kind of misfire detection based on a second spark strike attempt by the ecm in mind?

    I do know that most misfire detection is based on degrees of crankshaft acceleration after spark. (deg/second,etc)
    I might have an opportunity tomorrow to scope a 2010 chevy truck ignition "fire" signal to a coil. What I am looking for is feedback or no feedback on the line. Some coil drivers provide feedback on the "fire" line, with a magnitude of 5v max, which allows the "burn time" from the secondary side to be measured and compared to the rest off the cylinders.
    Last edited by vilefly; 1 Day Ago at 06:43 PM. Reason: another theory

  6. #276
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by vilefly View Post
    I think when the ABS is triggered
    Good thinking - I didn't realize ABS used torque limiting but that got me thinking about ASR. I took a look at the traction control table and I think it's possible to have a condition where negative spark advance could be commanded.

    Can anyone confirm the correct scalar for the 0x123A1 table? I have some xdfs with (0.062500 * X) and some with (0.250000 * X). If 0.0625 is correct there are only a few essentially "unreal" load ranges where negative timing might be commanded such as at 400 rpm and 100 map. If the other one's right there's a significant range.

    Quote Originally Posted by vilefly View Post
    Did you have some kind of misfire detection based on a second spark strike attempt by the ecm in mind?
    Sorry, nothing quite that ambitious. In it's current state I would characterize the maturity of the code as "nearly mastered crawling". I merely want to add some minimal failsafe logic so if the controller doesn't see a signal on the EST line in x amount of degrees it considers it a system fault and shuts everything down. That way if the EST circuit does happen to get broken it doesn't dwell more coils than the IGN circuit fuse can tolerate. Additionally, I didn't account for the possibility of negative spark advance so it could cause unexpected behavior if the PCM were to command it.

  7. #277
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by dzidaV8 View Post
    I'll work on your code to move more work on precompiler...
    Relative to my question in post #272, if the dwell tables can't be dynamically generated by precompiler directives - the idea crossed my mind of creating another conditional mode of operation to generate the initializers could be a better solution. That way the user could set the compiler directive and customize their dwell targets. Then when the mcu boots in this config mode the populate functions would spit out their customized tables to the uart as static initializers to be pasted directly into the source. That would eliminate the populate functions from being run at bootup in normal mode, shortening start time by 10ms or so, as well as alleviating the need to create yet another external spreadsheet tool to generate the tables.

    If I don't hear from you I'm going to code toward that goal as it's a very simple change.

  8. #278
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    This is the coil trigger signal from a 2010 5.3L silverado, no open circuits. So technically, we only know that it pulls down to exactly 4V, not sure what open circuit voltage is, due to a lack of time at the end of a friday....so I didn't think to do so...damnit. This engine uses the barrel shaped coils like spfautsch used in his videos.

    2010 silerado ign trigger.jpg

    So there is no feedback on that signal line to worry about when it comes to this type of coil.
    I will venture a guess that a 5V signal suffers a 1v-.8v semiconductor based voltage drop on one leg of a transistor tied to ground.
    Last edited by vilefly; 9 Hours Ago at 08:10 PM. Reason: more theory

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