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Thread: Crank timing for COP 4AFE/7Afe

  1. #16
    Junior Member Backyard Mechanic jondee86's Avatar
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    Default Re: Crank timing for COP 4AFE/7Afe

    I don't know how the ECU uses the Ne (rpm) signal, but looking at the 4-tooth wheel I can see that it will generate a signal every 90deg of cam rotation which is every 180deg of crank rotation. Sequential ignition on 4 cylinder engines (either COP's or distributor) requires an ignition event every 180deg of crank rotation. So if the pickup is located in a position that generates a signal at 10deg BTDC, then that will give the 10deg of ignition advance that most Toyota ECU's use for base ignition timing.

    A 24-tooth wheel on the cam has 15deg between teeth which equates to 30deg at the crank. Thus by counting teeth after a reset the ECU can calculate the crankshaft position every 30deg. I suspect (but don't know for sure) that by calculating the time interval between these teeth passing the pickup, the ECU can calculate the engine rpm.

    A 36-1 tooth crank pulley has 10deg between teeth This allows greater ignition timing accuracy but can limit maximum rpm as the time interval between teeth gets too short for accurate counting. If the Speeduino controls ignition and the ECU controls fuel they will be synchronised mechanically no matter what trigger wheel they use. I do think it might be easier if they both shared the Ne signal.

    Cheers... jondee86

  2. #17
    Learner Driver Backyard Mechanic
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    Default Re: Crank timing for COP 4AFE/7Afe

    Why don't you use a 24 tooth wheel on the crank pulley and make a sensor and mount to run of the camshaft?

    The dist you have now has a 24 tooth and a 4 tooth signal.
    The ECU does not know or care which cylinder is firing, as there is a rotor and cap to work out which cylinder needs the spark.
    This ECU cannot run sequential ing or fuel because of this.

    If all you want to do is make it tidy by running 4 coils,
    then why don't you use a 24 tooth wheel on the crank pulley
    and make a sensor wheel with 4 teeth and mount a sensor to run of the camshaft?
    They would have to be VR sensors and about the same resistance as the originals to work,

    then you could run 4 coils all triggered off the single IGT signal as per post #4 on here.

    Using a 7AFE oil pump with a built in sensor may be an option for you with a FE head,
    as they are a VR sensor,
    but so far cant get it to work with a GE head as the number of teeth to drive the cambelt is wrong.
    I am not sure what size the 4AFE cam wheels are, but I guess they will be compatable with 7AFE.
    - KE70 Corolla Dx -
    - 500hp+ 7AGTE 20V turbo -
    - MRS/Hayabusa turbo **sold**
    - TA63 3TGTE project in the build -

  3. #18
    Junior Member Backyard Mechanic jondee86's Avatar
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    Default Re: Crank timing for COP 4AFE/7Afe

    Something more to consider, although I haven't seen it done it could work

    To put everything on the crank and have it work with the factory ECU you need two pickups and a means of triggering them separately. So a conventional 12-tooth trigger wheel with a radially mounted pickup and two capscrews or similar into the face of the trigger wheel with an axially mounted pickup. With a bit of cunning it should be possible to design a bracket capable of holding both pickups and allowing a bit of adjustment for fine tuning the timing.

    If mounting to the crank becomes too difficult, then the same approach can be applied to mounting on the front end of the camshaft only with 24 and 4 tooth pickups. This doesn't offer any performance advantage over just leaving the base of the distributor where it is now except it could be lighter and more compact.

    The bracket needs to be rigid and have enough fixing points to avoid vibration as the gap between the tooth and pickup is small.

    Cheers... jondee86

  4. #19
    Forum Member 1st year Apprentice
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    Default Re: Crank timing for COP 4AFE/7Afe

    Have a look at this it might help
    https://racerxfabrication.com/mr2-ce...z-coil-on-plug

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