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GSX750ES : No ignition

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    #1

    GSX750ES : No ignition

    Before I started the nuts and bolts restoration ignition worked flawlessly. Now it doesn't.
    I verified all wiring are according to the attached electrical diagram including the 12v feeding (runoff switch dependent) to O/W coils wires.
    I checked the resistance of the signal generators : OK.
    I checked the resistance of the primary and secondary sides of the coils : only the secondary of coil responsible to cylinders 1+4 had bad infinite resistance.
    There is a test where you disconnect the plug coming from the signal generator to the igniter and by inducing the resistance of an ohm meter to 1+2 or to 3+4 legs you cause a spark: This test failed.

    1. Does this mean that the igniter is dead ?
    2. It worked before disassembly, any reason it would die with no usage ?
    3. Is there a way to measure the AC coming out of the igniter without using an oscilloscope ?

    DSC_2575-1.jpg
    Last edited by Guest; 10-30-2017, 05:16 AM.
    Tags: None
    #2
    I use a combination of D8EA plugs and the 5kohm NGK caps. In any case, I tried to bypass the caps just for testing purposes and still I saw no spark when running the starter.

    Comment

      #3
      Another test :
      I put a Fluke DVM on AC voltage mode connected to both CDI output to coils :
      In both coils inputs, reading was 0mv at rest and during startup it climbed to 50mv. Definitely faulty but still shows that something is coming into the CDI during startup but does not come out.
      My understanding is that the pickups are ok but CDI is dead...
      On the other hand, engine was not running but reving at close to zero RPM that starter enables...
      Last edited by Guest; 10-30-2017, 12:57 PM.

      Comment

        #4
        Originally posted by dpascal View Post
        Another test :
        I put a Fluke DVM on AC voltage mode connected to both CDI output to coils :
        In both coils inputs, reading was 0mv at rest and during startup it climbed to 50mv. Definitely faulty but still shows that something is coming into the CDI during startup but does not come out.
        My understanding is that the pickups are ok but CDI is dead...
        On the other hand, engine was not running but reving at close to zero RPM that starter enables...
        Why not follow the ignition checkout procedure in the factory manual? It would be much more conclusive than the test you did.

        Comment

          #5
          Ignition checkout procedure, described in pages 5-5 to 5-7 in the manual is included in the tests I described below.

          Comment

            #6
            Originally posted by dpascal View Post
            Ignition checkout procedure, described in pages 5-5 to 5-7 in the manual is included in the tests I described below.
            The manual tells you to measure the primary voltage with dvm set to AC?

            Comment

              #7
              The manual talks about resistance measurement of the primary which I did. It does not deal with voltage measurement which obviously should be AC. Coils accept AC and output AC.

              Comment

                #8
                Originally posted by dpascal View Post
                The manual talks about resistance measurement of the primary which I did. It does not deal with voltage measurement which obviously should be AC. Coils accept AC and output AC.

                Are you sure about this? I don't think there's any AC on the bike aside from the stator output. After the R/R, everything should be DC.
                Jordan

                1977 Suzuki GS750 (My first bike)
                2000 Kawasaki ZRX1100
                1973 BMW R75/5

                Comment

                  #9
                  Originally posted by hannibal View Post
                  Are you sure about this? I don't think there's any AC on the bike aside from the stator output. After the R/R, everything should be DC.
                  It is not so much the lack of AC, but rather how you should measure the voltages. The primary side of the coils is "chopped" DC that can be measured by monitoring the "DC" voltage as you slowly rotate the engine. The primary voltage stays high or low for periods of time that can me measured using a DC meter.

                  When points or igniter FETs are open then the coil voltage will be the battery voltage.

                  When the points are closed or the igniter FETs are shorted, the coil voltage will be close to zero (1.5 v).

                  It is in this closed state where the current runs through the coil and the magnetic field is being energized. It is ready to release that energy into a high voltage spike when the closed coil is opened.
                  Last edited by posplayr; 10-30-2017, 06:23 PM.

                  Comment

                    #10
                    I was able to find an oscilloscope reading of CDI voltages on the web that would explain in a picture what we're all trying to say in words.
                    The CDI output is a complex signal that consists of a (complex for itself) AC component riding on a DC component.

                    The top trace (Ch1) is stator output ( CDI input )
                    The lower trace (Ch2) is CDI output ( ignition coil input ).

                    images.jpg
                    Last edited by Guest; 10-31-2017, 12:58 AM.

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                      #11
                      I went on and measured DC on CDI outputs :
                      There is 12v going to Coil responsible for plugs 2+3 (no spark though)
                      There is 0v going to Coil responsible for plugs 1+4 (no spark)

                      Comment

                        #12
                        Originally posted by dpascal View Post
                        I went on and measured DC on CDI outputs :
                        There is 12v going to Coil responsible for plugs 2+3 (no spark though)
                        There is 0v going to Coil responsible for plugs 1+4 (no spark)
                        Reread my description, you need a 0=>12v transition to get a spark.
                        Aslo the gs does not use a CDI.

                        Comment

                          #13
                          As I predicted, the CDI was defected. Crossing with a CDI from a similar GSX750ES produced a spark on all plugs.
                          I bought an aftermarket CDI from a wonderful shop that does aftermarket digital high quality CDIs and it works. I have a 4 sparks !
                          HPI | Horse Power Ignition
                          http://www.hpi.be/item.php?item=CD2705D

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