Scope Set-up For CMP/CKP Relationship

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  • 89jyturbo
    Junior Member
    • Feb 2008
    • 4

    Scope Set-up For CMP/CKP Relationship

    Hello. I'm working on a Subaru WRX STi with an aftermarket ECM installed. Long story short, I am trying to do a cam/crank realtion test to verify proper operation of the variable intake cam system (called AVCS). I am somewhat new to using scopes, and need some info on how to set-up my Modis to perform this test. I think I could handle this if the car had a simple hall-effect (digital) CKP sensor, but this thing has a variable reluctor style sensor that outputs a/c voltage.

    Thanks for the help!
    -Kenton
  • 89jyturbo
    Junior Member
    • Feb 2008
    • 4

    #2
    I think I got it figured out. I was thinking the CKP sensor would need its own seperate ground to the scope, but actually it does not. Without a seperate ground, the pattern is just shifted up and does not cross zero like a normal a/c voltage signal would. I have my patterns up right now, but found low signal voltage from one of the cam position sensors, which I want to diagnose before going further.

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    • infil
      Member
      • Jan 2008
      • 45

      #3
      which ecu? UTEC?
      The cam and crank sensors share a common harness ground IIRC. If you think about going standalone from what i've seen the hydra is a sick sick sick setup, way beyond the other setups i've worked with(motec, aem, megasquirt etc)
      Infil
      Technical Auto Group, S.I. N.Y.
      Fast Times Performance S.I. N.Y.

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      • 89jyturbo
        Junior Member
        • Feb 2008
        • 4

        #4
        Thanks for the input. This STi has the Hydra installed. The cam sensors share a common power and ground source, not exactly sure why the one sensor is reading lower voltage than the other, but I determined that the Hydra ECU is in good control of both intake camshafts (this makes me believe the one sensor has a lower output voltage by design, as everything else checks out and the system does work). The customer had a profesional tuner work with the car but the tuner was concerned about a few things, one was an aparent loss of VE on the top end (hence the reason for checking AVCS sytem). I found that the cams advance in mid range, then retard back to nearly the same point as at idle on the top end? Is this normal? The map loaded into the hydra is hard to make sense of (no tangible numders are used as the AVCS map is not user tunable).

        I am not a professional tuner, but have had some fun playing with a few MegaSquirt systems before.

        -Kenton


        EDIT: Below is a picture I drew up to show what is going on with the AVCS, this is NOT the actual scope capture, just a simplified picture I made for the customer. Notice the one sensor has a lower voltage.
        Attached Files
        Last edited by 89jyturbo; 02-18-2008, 07:19 PM.

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        • Dynodave
          Applications Specialist
          • Oct 2006
          • 68

          #5
          Crank/cam relationship with CKP riding on a bias voltage


          Hi Kenton,
          That is a very nice drawing you have displayed. How did you draw it?
          I am not an expert on Subaru, but I have scoped a lot of signals.
          I can help explain why the analog CKP signal is running higher when it is attached to battery ground. This is because the CKP signal is running on a bias voltage. You would not be able to see the bias voltage if the leads were attached directly across the analog CKP sensor. The computers can use this bias for a number of reasons, one of which is for the PCM to know that the CKP pickup coil resistance is within and acceptable range.
          The Cam sensors appear to be digital hall effect sensors. In the picture drawn the Intake and exhaust cam sensors indicators and pulsing very close to the TDC indicator. One of the CMP (RH) sensors signal is high and then is being pulled low within the first notch of the CKP indicators missing tooth signal. The other CMP sensor (LH) stays low and the signal is pulsing high in the TDC just before the TDC indictor. I would like to see the actual MODIS waveform file, so I could raise the each waveform till the are all evenly on the screen.
          The waveforms appear similar to some other variable valve timing systems. By the waveform the sensors all appear to be operating as they should.
          Question does your factory scanner give you the degrees of advance of each cam?

          If not I would try to hook up the same engine and record the readings at the same RPMS and load to get a basis for comparison.
          There is a program that you can download form this site called "Shop Stream Connect" this will allow you to view these waveforms on a larger screen more accurately to compare signals more accurately.

          P.S What year and model was this? An Impreza Turbo 2.5L I am assuming.
          If you can email me the waveform I will try email you back and nice snap shot on the screen with a little more information explaining it.
          Take Care Dynodave.

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          • 89jyturbo
            Junior Member
            • Feb 2008
            • 4

            #6
            Thanks for the responses. I made up those pictures in paint just to show the customer. They are not very technical, I just wanted to show the cutomer that the cams were moving relative to the crankshaft. He wasn't sure that the aftermarket ECM was doing it's job.

            The car is an '05 WRX STi with an aftermarket Hydra ECM and a lot of hardware mods (upgraded turbo, FMIC, TGV delete, ect, etc). It had disappointing dyno results, so the customer had me as a third party do some checking on the operation of the AVCS and some other systems.

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            • Dynodave
              Applications Specialist
              • Oct 2006
              • 68

              #7
              Crank/Cam relationship Subaru with high perf module

              Thanks for the response, Kenton, If come across this vehicle I will try to test the CKP/CAM relation and calculate the degrees of the cam sensors advance/retard I will let you know the results if I find the same vehicle.
              Dynodave.

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