Fun things to do with a scope

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  • greasybob
    Senior Member
    • May 2008
    • 1590

    Fun things to do with a scope

    I thought this interesting. A 2012 Hyundai Santa Fe With complaint of blower motor not working on low speeds. Normally you would just suspect a bad resistor but even the manual temp control on this model uses a FET ( field effect transistor) The HVAC controller increases the voltage to the FET with each increase in desired speed increase. I back probed the control wire to the FET while I had my low amp probe around the blower motor supply wire. the problem was that the first 3 speed selections did not supply a signal to the FET. Bad HVAC controller. The cool thing was watching the increase amp draw with each speed selection matching the FET input. With seven selections you might not notice the fan speed increase but you can see the amperage draw.
    Attached Files
  • diesel71
    Senior Member
    • Feb 2008
    • 921

    #2
    nice work bob, it is cool to see how things work with a scope. never tried that test before thanks for sharing.

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    • greasybob
      Senior Member
      • May 2008
      • 1590

      #3
      I was supposed to go to a scope class tonight but couldn't make it so instead I have this.

      2008 Chrysler Aspen with a clicking noise coming from the back at start up for about 30 seconds or so. Found code B1057 in the HVAC module, Rear Blend Door Travel Range Too Large. Also would not switch from cold to hot. I suspected the actuator to be at fault so I ordered a new one. I got to wondering how does a 2 wire actuator know it's position, or, how does the control module know it's position. So I back probed the new actuator after installing and activated via the bi-directional test in my Verus. the bi-directional test commands the actuator in 20% intervals. As you can see in the screen shot the one wire only switches from ground to batt + depending on the last command from the HVAC controller. The other wire is pulsed at a timed interval to match the input from the controller. Once the command to 100% is given the actuator is pulsed once more to confirm that it has reached the end of it's travel. My guess is that the controller (module) monitors the amp load on the circuit which must increase as resistance to the actuators movement increases. This would explain the code and the clicking noise since the actuator must relearn it's position every time the ignition is cycled. The old actuator must not have been drawing enough amperage to indicate to the module that it had reached the end of it's travel (maybe stripped gears or slipping). I could re-install the old actuator and compare amperage draw and confirm ?...... Maybe another time
      Attached Files

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      • Witsend
        Banned
        • Nov 2012
        • 2942

        #4
        I Pull out the scope when the fun is over and something is kicking my ***

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        • Witsend
          Banned
          • Nov 2012
          • 2942

          #5
          P0300 ,208K 99 Astro van Vortec 4.3

          Miss fire History shows high counts on 4 and 5 . High KV on all cylinders. Clean MAF sensor and replace AIR HOG filter, Idles ok but still missing on acceleration(plugs, cap rotor and wires were replaced less than 2 years old , maybe 20K. I check fuel pressure is good and holds between 55-60 psi . I do injector balance test and flow seems equal ,each cylinder , fuel pressure drops to 48psi. Perform Cranking amps test (relative compression) and all looks equal . Replaced the plugs and noted cylinder 4 and 5 appear to have copper spark plugs and the rest are platinum plugs.(gap.060")
          Auto part Warrantied out the defective cap and rotor and now it runs well again without miss but the KV requirements in my opinion are still too high. Both o2 s are switching and long fuel trims actuallyseem a little on the negative (rich side) since cleaning MAF. Grams per second at idle about 5-6gpm
          I figure since it has a new cap and rotor and over 200k I do a CKP relearn.
          MT2500 Hold throttle WOT till fuel cutoff . Did 3 times and MT 2500 never confirmed it relearned anything or not, and I was afraid I would throw a rod if I persisted trying any longer, After it was returned to idle the battery light was on , belt was still on and alternator was not charging any longer . Can't get to back of alternator, and needed to test alternator B+ at wire next to fuseable link at starter. Yep alternator crapped out , revving up the engine so high several times to do a CKP relearn. Another Turd that fortunately for customer was also auto part store warrantied .
          Attached Files

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          • Witsend
            Banned
            • Nov 2012
            • 2942

            #6
            Next day Figured I drive the Astro Van and complete some OBD monitors while chasing down some parts for something else, and I see the temp gauge is climbing past the half way point and I smell antifreeze, turn on heater and it's blowing cool air. Retrieve pending code p0125. Uh oh . Sure enough the turd is low on coolant. Add the half gallon I find in van and get it back to garage. Seems the coolant pipe that GM routes right over the top of the alternator with the induction crimped end of the heater hose. That tube needs to be moved down either fore or aft of the alternator to facilitate the alternator removal and the 17 year old plastic 6 port heater control valve doesn't take kindly to any manhandling of attached hoses.
            Had to use this heater valve replacement as a reason to finally replace my pair of cable release hose clamp pliers.
            Lesson Learned: Do yourself a favor, don't be lazy, Cut the induction clamp off the hose and separate the hose from the metal tube, or the old plastic heater control valve port might break and make you eat the job.
            One good thing came out of replacing that 6 port heater control valve is discovering and replacing 2 rotted collapsed split sections of vacuum hose beneath it that attached to a ball shaped vacuum reservoir and a vacuum delay tee., which slightly mproved idle quality , HVAC air outlet function response time , and might have even lowered spark KV requirements, but obviously wasn't in the mood to hook up the scope again.
            Attached Files
            Last edited by Witsend; 10-22-2016, 11:18 AM.

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            • Bpilon
              Junior Member
              • Oct 2017
              • 15

              #7
              Hello, I'm new here and I think I will be watching your post, Thx for sharing your knowledge. I'm also new to the scope meter ect.

              Cheers !

              Comment

              • Glide
                Senior Member
                • Jan 2015
                • 303

                #8
                When doing CKP relearn you've got to apply the brake when doing the test or the fuel cutoff doesn't work until you hit the rev limiter and the test will not complete.

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