Ford Push start system diagnostic tip

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  • jpgarrido
    Junior Member
    • Dec 2006
    • 10

    Ford Push start system diagnostic tip

    This 1994 Econoline van with a 5.8L V8 had been to several shops to have a very intermittent and slight misfire diagnosed. This engine uses a distributor type ignition system with a remote mounted Ignition control module (grey ?Push Start? version).

    I could feel a brief hiccup type misfire occasional at idle.

    I knew the defect was probably not fuel delivery nor control as I could see no disturbance in the O2 sensor scanned graph. See Fig 1

    I caught this lack of spark event while watching the ignition secondary pattern drop out/disappear on the ignition scope. See Fig 2.

    I then scoped the Ignition module (ICM) to see what was happening.

    See Fig 3

    CH1-Power feed to ICM
    CH2-Spout
    CH3-Ignition primary control

    CH4-PIP


    When SPOUT rises the ICM is signaled by the PCM to fire the ignition primary. The Spout signal would not rise completely in this capture at about 38mS. It only displayed a runted attempt to rise. SPOUT finally did rise at about 41mS, a bit too late. Being the SPOUT pulse from the PCM did not reach sufficient amplitude the ICM did not fire the primary on time.

    The SPOUT signal is not rising signaling the ICM to fire the ignition primary as it should. As a result there is a missing firing event. This missed fire causes the RPM to slow down and the PIP signal to runt coincidentally at 38mS. Simply viewing the waveforms without a good understanding of these circuits might leave you wondering if the PIP signal from the distributor caused the problem or not. A further question might be is the defective SPOUT signal being caused by the PCM or the ICM? A quick way to tell is to remove the inline SPOUT shorting bar connector. This puts the system into based timing or ICM SPOUT only controlled timing. Now only the ICM controls dwell and firing point not the PCM.

    As you can see in the next capture.

    Fig 4:
    CH1-SPOUT from the PCM side of the shorting bar
    CH2-Spout from ICM side of the shorting bar
    CH3-Ignition Primary control CH4-PIP

    Now the ICM generated SPOUT, Ignition primary and PIP are all interacting normally with no misfiring occurring. The SPOUT signal from the PCM is still erratic and dropping out. Proof positive that the PCM was the cause of the erratic SPOUT behavior while the PCM was connected to the circuit through the SPOUT shorting bar connector. A new PCM fixed this one up.
    Attached Files
    Jim
  • john4842
    SDE Member
    • Oct 2006
    • 38

    #2
    Job Well Done

    Job well done

    Comment

    • keith
      Junior Member
      • Dec 2006
      • 2

      #3
      can`t see wave samples

      every time i try to view posted screen shot it tell me i have no (permission )

      Comment

      • howard1202
        Junior Member
        • Dec 2006
        • 3

        #4
        no images

        same here. i've tried to contact someone about problem but no reply.

        Comment

        • Joshua Covington
          Senior Member
          • Aug 2006
          • 319

          #5
          Originally posted by howard1202
          same here. i've tried to contact someone about problem but no reply.
          Thanks Howard1202. First, all registered users should be able to see images in non-private forums so I'll look into that and get back to you guys pretty quick.

          Second, I PM'd you about your attempt to contact us so we can take care of whatever might have happened.

          Thanks,
          Josh
          Snap-on Diagnostics
          Program Manager

          Comment

          • Joshua Covington
            Senior Member
            • Aug 2006
            • 319

            #6
            Images should be visible now. Let me know if you dissagree
            Snap-on Diagnostics
            Program Manager

            Comment

            • howard1202
              Junior Member
              • Dec 2006
              • 3

              #7
              much better

              much better thank you

              Comment

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