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Thread: Understanding Timing Coolant/IAT retard tables

  1. #1
    New Member
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    May 2021

    Default Understanding Timing Coolant/IAT retard tables

    I'm trying to grasp the tables used to reduce timing at increased IAT and ECT temperatures. There are two tables used for this which I'm including. These are the stock tables.
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    As IAT and ECT raises, the ignition delay decreases and I'd want to reduce the timing most at these points. I'm trying to understand what is actually happening with these tables. Let's say at the highlighted points where the multiplier is 0.40 and the retard is 5. To me this would be 5*0.4=2. Is this the value that is subtracted from the main timing table? When the value is negative is it actually increasing timing?

    Also wondering what a multiplier of 0 does? Since I want to retard the most when the multiplier table is at "0" on the outside rows and columns, I'd expect to see the opposite with a value of 1. Any input would be appreciated.

    2008 F550 6.7 swapped running CM849 ecu

  2. #2
    New Member
    Join Date
    Aug 2023


    I know this is old but someone might see this and get confused. Your understanding is backwards, it's not retarding 5* as that would be counterproductive of what you need and you'd have to have a negative value instead of a positive in order to do that. If you have a value of 5*, that is asking to add 5* before the multiplier takes effect. So you have a value of 5* times the multiplier or in your example 0.4 thats 5 times 0.4 which equals 2* of advance. That means that value of 2* will be added onto the base map. Say your base map is asking for -2, the math is -2+2=0* so your injection timing would start 0* BTDC instead of the base map's -2 value... As the multiplier decrease you will have a lessor and lessor value added until your multiplier reaches 0, because 5 times 0 is 0 or your base injection table value of -2 is now -2+(5x0)=-2 so no timing is added to the base map. This is why the multiplier value decreases with temp increase, as you've stated less advance is required with temp increase. Your base map should be set at temp and then the numerical number and multiplier added as required.

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