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Thread: DIY LTCC or similar system for LT1s

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  1. #11
    Fuel Injected!
    Join Date
    Oct 2013
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    1,022
    spfautsch

    At this point, I definitely would bet against switching to the next coil on each low-res crank signal working correctly. I too highly doubt that the PCM could command 46* advance at any rpm and still restrain the coil charging time to be between two low-res signals. I'd bet that the PCM turns the coil back on to fire the next cylinder coil before the low-res pulse identifying the cylinder that just fired even appears.

    This doesn't make it that much more difficult to use 8 coils. Do it by using the opti signals to determine which coil to connect next and the EST to switch to that coil. In that way, you connect the next coil required immediately after the previous coil has fired. This doesn't give the ideal dwell time, but would work. However, this eliminates the main advantages of using 8 coils. A proper 8 coil system will overlap the operation of the 8 coils to maintain the ideal dwell time for the coils at every rpm. That's too big an advantage to give up.

    I too would bet against the LTCC module simply multiplexing EST line. It is advertised as having more spark energy which likely means it does maintain the ideal dwell time for each coil. This means it also does some much more complicated calculations to be able to switch 2 coils on at once. It doesn't need to do any timing calculations, but rather just use the EST and rpm along with the desired dwell time of the coil to calculate the time when the next coil should turn on. The EST can still be used to trigger the correct coil firing. In this way, even if there was some error in the dwell timing calculations as the engine operating conditions vary, it wouldn't affect the actual engine timing. Or in other words, the calculations don't have to be as exact as doing timing would require for it to still work just fine.

    I recall posting something about having a full plan before going off half-cocked on a solution fairly early in this thread. It seems to have taken another 100+ posts to start coming up with a plan that could work but I think there is a decent understanding of what is required to properly do a coil near plug system now. It's much more complicated then just multiplexing the coil driving wire.
    Last edited by lionelhutz; 11-11-2017 at 07:22 PM.

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