Testing methods for Light Misfires

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  • jm43130
    Senior Member
    • Apr 2008
    • 182

    #16
    In a reply to Witsend. ON the old scopes, didn't they use to tell that the flat plug firing line, after to spike to start spark plug, if it sloped upwards, didn't that tell that there was valve problems.

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    • Witsend
      Banned
      • Nov 2012
      • 2942

      #17
      In a reply to Witsend. ON the old scopes, didn't they use to tell that the flat plug firing line, after to spike to start spark plug, if it sloped upwards, didn't that tell that there was valve problems.
      I'm pretty sure a gradual slope upwards is normal, but on a throttle snap ,a very short line that suddenly spikes upward " is a classic no fuel misfire"

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      • diesel71
        Senior Member
        • Feb 2008
        • 921

        #18
        Originally posted by snapon20r
        So just curious how you adapted the pressure transducer to a spark plug compression tester? Would you have a picture of it??
        IMG_7299.jpg
        20151112-1558-1.jpg
        20151112-1625-1.jpg

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        • Witsend
          Banned
          • Nov 2012
          • 2942

          #19
          So on the end of the hose that normally would have threads you would screw in , instead you got an easy shove in non threaded end with an O-ring, you need to hold firmly in holes?

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          • diesel71
            Senior Member
            • Feb 2008
            • 921

            #20
            Originally posted by Witsend
            So on the end of the hose that normally would have threads you would screw in , instead you got an easy shove in non threaded end with an O-ring, you need to hold firmly in holes?
            you screw it in,there are threads on it. on that end you can remove part of it to use the bigger sized spark plug threads. i believe one size is 5/8 and the other is 13/16.

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            • crackerclicker
              Senior Member
              • May 2008
              • 400

              #21
              Originally posted by Crusty
              Cylinders would fire properly and then not fire properly and that older ignition trace used to show that if you watched closely. It's been one of my bugaboos for several decades and yes I am fully aware of what the new scopes can do, but I'm old enough to recognize what they don't do anymore as well
              I'm fairly certain we've argued on this or a similar topic before, but I'm unconvinced you've truly explored all the options available. Personally I find only a little value in examining secondary the way you describe, however I believe what you desire is available in Picoscope's "rapid trigger" feature (other quality DSO manufacturers likely have a similar feature).

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              • Crusty
                Senior Member
                • Dec 2007
                • 2450

                #22
                Originally posted by crackerclicker
                I'm fairly certain we've argued on this or a similar topic before, but I'm unconvinced you've truly explored all the options available. Personally I find only a little value in examining secondary the way you describe, however I believe what you desire is available in Picoscope's "rapid trigger" feature (other quality DSO manufacturers likely have a similar feature).
                I'm unconvinced you've stood in front of a vehicle watching the scope screen and both heard the misfire and seen the misfire at exactly the same time, and I do mean exactly, positively identifying the cylinder or multiple cylinders, which used to be a normal capability of older mainstream scopes prior to the digitizing that began in the early 1980's, not just one specialty scope using one feature.

                Whatever else is going on, the desired result is in fact that secondary firing of the plug, in the hole, under compression, with fuel delivered, completing the burn and the expanding gasses pushing the piston down.
                Whatever the primary ignition is doing does not always translate to the secondary doing what it is supposed to do.

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                • snapon20r
                  Junior Member
                  • Jan 2012
                  • 20

                  #23
                  Originally posted by diesel71
                  [ATTACH]20033[/ATTACH]
                  [ATTACH]20034[/ATTACH]
                  [ATTACH]20035[/ATTACH]
                  Thankyou diesel71 for your pictures and info, that will be a big help.

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                  • snapon20r
                    Junior Member
                    • Jan 2012
                    • 20

                    #24
                    And thankyou to everybody else for your replies.

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                    • crackerclicker
                      Senior Member
                      • May 2008
                      • 400

                      #25
                      Originally posted by Crusty
                      I'm unconvinced you've stood in front of a vehicle watching the scope screen and both heard the misfire and seen the misfire at exactly the same time, and I do mean exactly, positively identifying the cylinder or multiple cylinders, which used to be a normal capability of older mainstream scopes prior to the digitizing that began in the early 1980's, not just one specialty scope using one feature.
                      Canada’s Distributor For PicoScope Automotive Oscillocopes


                      Give him a call, he's a big fan of Rapid Trigger.


                      Originally posted by Crusty
                      Whatever the primary ignition is doing does not always translate to the secondary doing what it is supposed to do.

                      Agreed, not sure what your point is.

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                      • Joe Rappa
                        Snap-on DSD
                        • Aug 2007
                        • 2050

                        #26
                        There are some folks that are VERY accomplished when it comes to analyzing vacuum waveforms from the intake and pressure waveforms from the exhaust. If it's a mechanical problem with the engine(and you're looking for sticking valves), you can certainly see waveform changes if you do those measurements. I've got a friend that swears by the Sen X First Look.

                        Joe
                        "You don't build a reputation on what you're going to do"
                        Henry Ford

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                        • Crusty
                          Senior Member
                          • Dec 2007
                          • 2450

                          #27
                          Originally posted by Joe Rappa
                          There are some folks that are VERY accomplished when it comes to analyzing vacuum waveforms from the intake and pressure waveforms from the exhaust. If it's a mechanical problem with the engine(and you're looking for sticking valves), you can certainly see waveform changes if you do those measurements. I've got a friend that swears by the Sen X First Look.

                          Joe
                          Good point Joe. I've been so used to hooking up vacuum gauges to see how the engine is breathing that it's second nature and I had forgotten to even mention it. Fundamentally the valves dictate how the engine breathes.
                          It is getting harder and harder to access a vacuum source on todays' engines but worth the effort.
                          Diesel engines don't need the spark plug to complete the combustion so I can certainly see where the pressure transducer in place of the glow plug would work just fine. It eliminates a very necessary part of the entire cycle in a gasoline application though.

                          Question; does the First Look system have a quick and easy way to measure both the air entering the engine (via air in the intake duct, OR, the vacuum) and the exhaust out at the same time, and then graph the two well on a scope screen-??

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                          • Crusty
                            Senior Member
                            • Dec 2007
                            • 2450

                            #28
                            Originally posted by crackerclicker
                            http://www.mikejonesauto.com/

                            Give him a call, he's a big fan of Rapid Trigger.


                            Ummm it's still one system, not the mainstream norm the way secondary ignition scopes used to be


                            Agreed, not sure what your point is.
                            Ummm misfires...

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                            • crackerclicker
                              Senior Member
                              • May 2008
                              • 400

                              #29
                              "You can lead a horse to water . . . "

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                              • Crusty
                                Senior Member
                                • Dec 2007
                                • 2450

                                #30
                                Originally posted by crackerclicker
                                "You can lead a horse to water . . . "
                                Young bull, old bull...

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