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Cyl & Sync Settings with 36 crank wheel

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  • Cyl & Sync Settings with 36 crank wheel

    Hi, Is there a way to calculate the divider offset based on the information below? And are the settings I listed for the I/P Cylinder & Sync correct for the below crank and cam sensor setup. Thanks.

    SM4 - Firmware V1.09_6
    Engine Toyota 4A-GE
    Cylinder sensor setup: Honeywell GT101 Gear Tooth Sensor, crank wheel with 36 evenly spaced teeth, with a tooth triggered at 0º BTDC
    Sync sensor Setup: Older Toyota Distributor with sync set to occur at approx 5º ATDC on No.1 combustion stroke.

    Trig decoder: Divider HiSpeed 2S
    Tester: Disabled
    EFP divider factor: 18
    Divider offset: ??
    Trigger event/cycle: 4
    Cylinder I/P lead: 60
    Digital angle filter: Fast
    Clylinder sensor: Hall
    Cylinder trig edge: Falling
    Cylinder I/P filter: Fast
    Sync sensor: Reluctor
    Sync trigger edge: Falling

    One more thing. The customer supplied an older style Toyota distributor to source the sync signal. It came with 4 even spaced teeth and a single tooth. It uses two circular connectors. The one for the single tooth sync has a green and a black wire. I couldn't find any information on which was +ve and -ve, except for a diagram from another vehicle which showed the same connector with +ve being the wire closest the connector clip, so I used that wire (green) for +ve. You can see the connectors in the picture in the link. if anyone knows whether or not I have this correct, please let me know. Thanks again.

    Edit, not sure why but the link keeps getting edited down to just the main page. full link below, but you will need to copy and paste it.
    Last edited by hioctane; May 21st, 2019, 03:47 AM.

  • #2
    I got it sorted, using 6 for the divider offset (sync signal six teeth away from 60º cylinder tooth). Timing was a bit erratic and I didn't like the idea of relying on the distributor, as any small change in adjustment would throw things out, so I removed one the teeth on the 36 tooth cylinder trigger wheel and made it missing tooth. Timing was then rock steady, and cylinder sync was between 45% and 50%. The scope showed distributor reluctor signal was OK so it seems the polarity is correct.


    • #3
      Good idea going to a missing tooth with 36 teeth. At best you would have had +/- 5 degrees of scatter in the Sync before the Sync pulse could "trip over" a crank pulse and jump the timing by 10 degrees.

      For future reference with a divider pattern the crank tooth referred to by the Offset parameter is before the Sync pulse (or Sync event in the case of a complex pattern) counting from 0. So for 36 teeth occurring at TDC, 10, 20 etc and the Sync pulse at 5 deg ATDC Cyl #1 you would have Offset = 0 referring to the TDC crank pulse, Offset = 1 referring to the 10 deg BTDC crank tooth, Offset = 6 -> 60 deg BDTC, etc. If the Sync had been 5 deg ATDC Cyl #4 the crank teeth would have been 360, 370, 380 etc depending on Offset value.
      For the missing tooth pattern the Offset references crank teeth before the gap but also needs to include any phase offset for Sync position.

      On Toyotas I have seen the black wire generally being a +ve signal, but that has been on the car wiring, not necessarily on distributor wiring which sometimes seems to be different colours to the other side of the loom plug. If you don't have a scope to check a reluctor polarity you can often use the software scope log if you are sure the other trace is correct. A correctly wired reluctor will show a constant position for the falling edge relative to the crank trace teeth regardless of engine speed. If the falling edge moves with engine speed the reluctor probably has the polarity swapped. Note if the tooth is really narrow it might be difficult to check by this method.


      • #4
        Hi Ian,

        Thanks for that thorough reply, it's appreciated. Exactly as you predicted, I was seeing the timing occasionally jump by 10º, so that was the nail in the coffin that lead me to go missing tooth.

        Got the car tuned today, and it runs flawless to 9,200rpm.


        • #5
          Happy to report the car ran flawless for Rally Barbados, won it's group in every stage and finished with a 4 minute victory margin! Thanks for the help with the trigger settings.

          I have an install on another rally car coming up (4 cylinder) and I checked the crank and cam setup. Below is a picture of the crank trigger wheel setup on the car. I want to confirm something, when using a missing tooth setup does sensor location factor into the settings or only the number of teeth from the missing teeth to the trigger tooth (in this case 60? BTDC)? Also I can't remember is 55? ATDC is within the acceptable range for a cam trigger?

          Would these be correct:
          Trig decoder: M02
          EEP divider factor: 18
          Divider offset: 7 pulses
          Number missing teeth: 1
          Trigger events/cycle: 4
          Cylinder I/P lead 60 degrees

          EDIT: Just realized the diagram is wrong, it should read "Sync signal occurs at 55 degrees ATDC on No. 1 combustion stroke"

          Last edited by hioctane; June 29th, 2019, 11:42 PM.


          • #6
            Edit for further clarification.

            Is the diagram showing the crank wheel position when the engine is at TDC? That is, the tooth at the top of the diagram passed the crank sensor 90 degrees ago?
            Last edited by Ian; June 30th, 2019, 11:00 AM.


            • #7
              Hi Ian, the diagram shows the positions at TDC No. 1 compression stroke, so yes, the TDC tooth marked with green would have passed the sensor 90 degrees ago.


              • #8
                Crank teeth always need to be considered relative to the crank sensor position. If I have interpreted the diagram correctly it looks that the missing tooth occurs 70 deg BTDC. That gives you a few options.

                The tooth occurring immediately before the missing tooth would be 80 deg BTDC and would be Offset = 0. Conversely, the tooth occurring immediately after the missing tooth would be 60 deg BTDC and would be Offset = 16 (The 16 comes about from (Divider - 1) - # of missing teeth being the first tooth after the gap). Also in consideration would be 90 deg BTDC (Offset = 1) or 50 deg BTDC (Offset = 15).

                Depending on things like the type of crank sensor, the tooth profile and also the depth of the missing tooth region there could be a slight position error in the sensor waveform on the teeth either side of the missing tooth so it would be prudent to reference off one of the other teeth.


                • #9
                  Many thanks Ian. I take it the cylinder sync triggering at 55 degrees ATDC on the combustion stroke is fine?


                  • #10
                    Hi Dennis, that Sync position should be fine. The Lead Angle pulse for the next cylinder will be 180 deg from the Lead Angle you choose (for that engine) so that would be 90 deg ATDC for a 90 deg Lead Angle which is plenty of room for a 55 deg ATDC Sync. For that M02 Trigger pattern the main Sync rules are that the Sync doesn't occur in the missing tooth gap in the crank or too near to the Lead Angle crank pulses.


                    • #11
                      Hi Ian, Thanks so much for the help., it's always very much appreciated.


                      • #12
                        Hi Ian, Just a quick reply to say the car started fine, using the 90 degree lead angle settings. Cylinder sync is solid at 78% at anything over 1400 rpm. It is a bit hard to start sometimes, but I find the same thing with another rally car using the Magnetti Marelli reluctor sensor. They don't do so well at lower rpms. When I get a chance I'll do a log of the car starting.

                        Another quick question. The ECU is chip version 1.09_6, and I notice the ign mod 2 is greyed out. Is this not available with the v1.09? I used Ign mod 3, via a switch, to subtract timing for when the stages are wet. The customer would also like another setting that is slightly less aggressive with timing advance. Basically he wants aggressive, normal and reduced (wet).


                        • #13
                          Ian has left the building. I am now offering a paid support option.
                          He gets his lap dogs to do his talking for him. Buzzard is a good example.


                          • #14
                            I had been working practically 2 weeks straight trying to get several cars sorted out and building a high quality mil spec motorsport harness for this rally car, and getting it ready for this weekend, so last night, being very low on sleep and on energy, I was obviously having a little brain fade.

                            Remembered this morning: Menu M2 -> Ignition Trims -> Ign Mod setup


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