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Thread: How idle speed, corrections to idle speed and trims are calculated.

  1. #1
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    Default How idle speed, corrections to idle speed and trims are calculated.

    Hi im Mike i live in New Zealand im a mechanic still new to efi live but no stranger to tuning. I use to have a dyno at my workshop but i didnt use it alot so it got sold to buy more useful equipment a few months ago. Anyway i have a work car a holden statesman with a ls1 with a 232/236 cam in it dyno tuned it fine but never got it to idle perfect its hard to start when its hot and stalls when putting it into gear when its cold.

    So how is everything calculated? ill try break it down but have some parts i cant work out. So if anyone can help me fill in gaps add details and tell me if im wrong it will be very helpful.

    So first of all VE table and spark are done and im just trying to get my head around how it makes adjustments. To make it easy well say the engine is at operating temp, closed loop, Idle mode, In park.


    Desired idle speed (Target 850Rpm)

    Desired airflow (Target 10 G/s)
    Base spark (Target-24)

    RPM Air flow control (60rpm/1.8sec)
    <Rpm set point adjust>
    Under/Over speed timing correction (-10/+10)

    Air flow learning (60rpm/1.5sec)

    Short term idle trim (+/- 1G/s)

    Actual idle speed

    Is this how it works if so how does it decide between ign timing or air flow? Is it possible to change it to say just spark control or just air control? How is Rpm set point adjust changed eg. 0= no correction 5=some 10=alot?

    Cheers

  2. #2
    Joe (Moderator) joecar's Avatar
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    Hi Mike,

    Look at the P/N and In Gear desired airflow tables.


    More info:
    Idle-Tuning-Helpful-Info-Inside
    Idle-Tips-amp-Tricks

  3. #3
    Lifetime Member limited cv8r's Avatar
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    There are two idle tabs in the software, one for airflow and one for spark. Pic attached. Most of its pretty strait forward
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    It's all good until it goes "Bang"

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    When i first tuned it i run RAFPN and RAFIG then logged MAF grams/sec Average vs ECT and tweaked the desired airflow tables so it matches the measured airflow. I also adjusted the spark over and under speed tables.

    So this week i had a play with the desired air P/N table and could make it idle and go into gear etc. Now about once a min the idle speed goes up and down by its self i think its the STIT or LTIT maxing out? and when i take it out of gear into park the revs shoot up then come back to normal after a second or two. So im trying to work out how the RPM set point adjust works mine is set on 2 i. also can you set it so idle speed is controlled by ignition timing and not so much by IAC im thinking with a really lumpy cam it may work better that way.

  5. #5
    Joe (Moderator) joecar's Avatar
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    Post current tune and log files.

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    Lifetime Member limited cv8r's Avatar
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    you could try zeroing out the airflow correction tables
    It's all good until it goes "Bang"

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