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SM4 trigger accuracy with more or less teeth?

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  • #31
    This is a very good and informative thread.

    I don't have an SM4, I have a SMC v1.92.

    I was running a 60-2 crank trigger setup and I'm in the process of changing it over to a pulse-per-cylinder arrangement. I had performed the high speed (internal resistor mod) to the SMC, but was still having issues with sync/cyl percentage. It was rock solid at 38 degrees during cranking, but during running it would bounce all over the place and sometimes go as high as 103 degrees. I was told that the SMCs don't like the multipule pulses from the 60-2 and that I should change it to the pulse-per-cylinder setup.

    I haven't got the setup on yet so I'm hopeful that after reading this thread I'm going in the right direction. I should have it running next weekend.

    By the way, it is a four cylinder with 2 timing "triggers" now.

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    • #32
      Originally posted by gti View Post
      Yes, I do have some used 1.06 chips.

      You have pm if you didn't already see it ?

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      • #33
        Originally posted by Kelly2264 View Post
        still having issues with sync/cyl percentage. It was rock solid at 38 degrees during cranking, but during running it would bounce all over the place and sometimes go as high as 103 degrees.
        I did not do so many SMC motronic triggering, but this seem not okay. I beleive you mean sync/cyl above when you wrote degrees so I would first check the polarity of the inductive trigger. Check with a scope you got the positive wire connected to the+Ve red wire on the reluctor.
        Robert Jansson
        MRM-Racing

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        • #34
          I have only ever done one 60-2 on a SMC V1.92. It was faultless. What was the engine ?

          Chris
          He gets his lap dogs to do his talking for him. Buzzard is a good example.

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          • #35
            What was the engine ?
            It is an aircooled 4 cylinder Type 1 VW. The crank sensor is from a Porsche 996 (reluctor) with a reluctor interface. The "cam" signal is from a modified Golf Dist. (hall) (it has a single window in the dist. from a Vanagon).

            I believe you mean sync/cyl above when you wrote degrees
            You're correct, I meant percent. I had gone over most of the wiring issues (what could be wrong and what was right) with Ray. But, this one thing seems to be "hounding" me. I PM'd a couple of AC VW guys on the old forum and some suggested getting rid of the 60-2 for they had had problems in the past with this and SMCs. It's not that difficult to change it over, so...

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            • #36
              I did a couple of Peugeots using the Bosch 60-2 trigger with SMC. It reported sync error when the engine was being cranked, and it took a bit longer than normal to start - longer cranking time. Other than that, it ran OK. Sensor polarity is most important. If you get it wrong, it gives you all sorts of problems.

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              • #37
                Thanks for the input guys !

                I will definately be rechecking my polarity to insure it is wired right way around.

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                • #38
                  Originally posted by gti View Post
                  I did a couple of Peugeots using the Bosch 60-2 trigger with SMC. It reported sync error when the engine was being cranked, and it took a bit longer than normal to start - longer cranking time. Other than that, it ran OK. Sensor polarity is most important. If you get it wrong, it gives you all sorts of problems.
                  What engine model did you work on Peugeot? Does it have cam sensor?

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                  • #39
                    What kind of things does wrong sensor polarity cause?

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                    • #40
                      I can think of many........if it is a multi-tooth trigger the ignition can move with rpm, If 60-2 (or other missing tooth) it can result in sync errors during crank/start/run, engine will only run to a certain rpm before missing or just random errors. I remember one other brand that stated "If polarity is wrong some weird things may happen" !
                      Robert Jansson
                      MRM-Racing

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                      • #41
                        To be a bit "electric", but yet slightly simplistic: The sensing coil in an inductive pickup is wound so that it has one "hot" connection and one "cold" connection. The same goes for the signal receiver in the ECU. It has one "hot" connection that is sensitive, and one "cold" side that is less sensitive and primarily there for closing the "current loop" in the "differential signal pair" from the pickup coil.

                        So one can not just swap the positive and negative side on the sync inputs. But rather must figure out if the trigger edge is positive of negative. Some manufacturers detect trig events with bumps, and others detect with holes in the timing disc. This tells if the correct trigger edge is positive or negative.

                        Also, The correct detection edge on an inductive pickup is always the second edge that occurs, (that is, when the bump or hole leaves the pickup), since the first edge will always be much weaker since there will be less "magnetic flux" going from an unenergized state, than going from one energized state to an energized state of the opposite polarity.

                        Looking at the signals with a scope, one will see that the "hot" signal is slightly bigger in volts than the "cold" signal.

                        The "hot" signal must be connected to the positive sync input.

                        The trigger edge that one configures for the sync input in the cal file must be that of the second edge on the hot side.

                        Hope this explained more than it confused.
                        Johan Jansson, +46-708-280832

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                        • #42
                          Thank you!

                          I thought that was a very good "simplistic" way to describe the events that take place.

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                          • #43
                            I've been having a bit more of a play with this timing thing. Its most deffantly a piston acceleration problem, with more timing its worse and less timing its not so bad but still way out.
                            This is because more timing must be having a greater effect on piston speed on the power stroke.
                            With only two crank teeth for a 4 cylinder engine you would think there would be a need for an engine mass/cylinder cc size filter in the software.
                            I can see a 2L subaru with the stock 12-13kg flywheel wouldn't ever have a problem. But when you have a 2.5L with 600cc pots and a 6kg flywheel i think this is where the limit may be?
                            I wouldn't have thought a faulty chip would cause this as everthing else works fine?

                            Also if i was to have more teeth on the crank trigger cant the autronic know its still only a 4 cylinder and only still sample the load at the normal place in stead of every tooth, this seems a bit odd if it cant ?

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                            • #44
                              Ian recomended you to change chip, and yeas Ian decribed how the Sm4 senses the load, each "cylinder event". So for doing it right you shall use a divider to still have 4 events cycle. So for this you need a chip with divider meaning 1.06 or newer......
                              Robert Jansson
                              MRM-Racing

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                              • #45
                                I've had a donation out of good faith and will have a 1.06 to try and i'll report back on the out come.

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