Cylinder Performance Test

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  • No-Start
    Senior Member
    • Oct 2006
    • 932

    #16
    Hi CdanB6,

    May I suggest that you try an external trigger by using an inductive probe on another channel. That way, you can "see" the trigger unlike the internal one.

    If you don't have one, you can order them through AES.

    Automotive diagnostic equipment sales and support for professional automotive technicians, schools, instructors, and trainers. Services include custom manufacturing and product development.


    No-Start.

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    • MasterWrench
      Senior Member
      • Oct 2006
      • 1186

      #17
      I have not been able to find my notes from the "Pro-Tech" class I took. In the class it seems to me that the firing order was at the bottom of the screen and no external trigger was necessary. When I get home tonight, I will email them and see if they can send me the info.......
      MasterWrench

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      • Nick
        Senior Member
        • Oct 2006
        • 550

        #18
        I use a high amp probe around a battery cable. Sync it with sylinder number one to find weak holes.
        Ill see if I ca find a screen shot.

        Granted this is a cranking test and nothing any old engine analyzer didnt do. Or new one for that matter.
        Last edited by Nick; 02-08-2007, 11:08 AM.
        Mechanic-Instructor-Mobile Trouble Shooter

        Autotechdiagnostics.com

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        • Nick
          Senior Member
          • Oct 2006
          • 550

          #19
          Here's a GM 4.3 with a bad hole. It had a consistent misifre. A simple cranking amperage test shows the base engine failure. Channel two is synced to cyl #1. the firing order is 1-6-5-4-3-2. Cylinder five is the weak hole, shown by the lower amp draw.
          Taken with a high amp probe.

          Last edited by Nick; 02-10-2007, 10:46 AM.
          Mechanic-Instructor-Mobile Trouble Shooter

          Autotechdiagnostics.com

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          • mr toyoda
            Junior Member
            • Apr 2007
            • 1

            #20
            wavepoint?

            hi guys

            what is wavepoint
            this is something snap on sells?
            /

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            • mbenoit
              Junior Member
              • Apr 2007
              • 6

              #21
              Hi I wrote Snap-On tech support about doing a relative compretion test using my V- Pro and a high amp probe and this was there response "Marc, this is the response I got from one of the Vantage Guys. Let me know
              if this works for you.

              Use Ch1 volts DC 1 volt scale and then use the conversion supplied by the
              Manufacturer of the Probe.

              Hope this help.

              Snap-on Diagnostics Support

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              • tmm1976
                Junior Member
                • Aug 2008
                • 5

                #22
                relative compression test

                I did a RCT on my voyager with a modis and a snap-on low amp probe and I got this. you may need to download the file and zoom it up to 16x.
                Attached Files

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                • bwrench
                  Senior Member
                  • Aug 2008
                  • 157

                  #23
                  Originally posted by tmm1976
                  I did a RCT on my voyager with a modis and a snap-on low amp probe and I got this. you may need to download the file and zoom it up to 16x.
                  When doing a relative compression test, you should use a high amp current probe, or use a different scale on your scope. Why did you have the scope set on AC coupling? This is why the scaling is all wrong. Try your capture again with at least a 500 ms time base,,,, or enough time on the screen to get one whole engine revolution on the screen. Take your scope off of AC coupling, so that you can get the current properly scaled. Since you are using a low current probe, you should use a voltage screen with 2 volts on the screen. Then you will have to calculate the current scale. The best tool for this really is a high amp probe. The capacity of your low current probe is being pushed beyond it's limits, since the max capacity of your probe is 40 amps, and this starter is pulling at least three times that much current.

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                  • smj1995
                    Member
                    • Dec 2007
                    • 93

                    #24
                    Originally posted by bwrench
                    Why did you have the scope set on AC coupling? ...The capacity of your low current probe is being pushed beyond it's limits, since the max capacity of your probe is 40 amps, and this starter is pulling at least three times that much current.

                    Having the AC coupling turned on allows him to use the low-amp probe to check relative compression. I agree that a longer sweep time would make it easier to compare the amp draw of the starter between compression strokes. Personally, I don’t try to trigger off of an injector and I don’t worry about calculating the scale. I’m just looking for an obvious mechanical problem with the engine. If I see considerably less draw on one of the cylinders, then I know that there is a mechanical problem in one of the cylinders and the customer gets notified of a potentially expensive repair.

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