93 dakota help

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  • plus2
    Junior Member
    • Nov 2009
    • 26

    93 dakota help

    I have a 93 Dakota 3.9L that cuts out and misses between about 150 and 180 degrees then cleans up. Crank sensor, distributor bushing and gear were replaced before I bought it. Distributor seems fine, nothing lose or worn(but rotor still moves about 3/16" after repair). I can't set dis. sync with modis, reading stays at 0 when I turn dis. so I set it with DVOM. It's probably not set right now because I was moving it looking for improvements. ASD does not cut out. I tried a used(unknown) PCM with same results. I'm hoping I can send some movies for someone to examine for me. If so tell me what to scope and send. Thank you
  • Crusty
    Senior Member
    • Dec 2007
    • 2450

    #2
    Originally posted by plus2
    I have a 93 Dakota 3.9L that cuts out and misses between about 150 and 180 degrees then cleans up. Crank sensor, distributor bushing and gear were replaced before I bought it. Distributor seems fine, nothing lose or worn(but rotor still moves about 3/16" after repair). I can't set dis. sync with modis, reading stays at 0 when I turn dis. so I set it with DVOM. It's probably not set right now because I was moving it looking for improvements. ASD does not cut out. I tried a used(unknown) PCM with same results. I'm hoping I can send some movies for someone to examine for me. If so tell me what to scope and send. Thank you
    Sounds like it could be acting up just as it goes into "closed loop" when the ECM starts to adjust fuel delivery based upon oxygen sensor feedback.
    Check your fuel pressure, the oxygen sensor(s), fuel trims both long & short term.
    How long does the condition last for? Does it act up only under load or only at idle, or both? Check the harness at the right rear where the wiring runs up the valve cover to the ignition coil too.

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    • plus2
      Junior Member
      • Nov 2009
      • 26

      #3
      Fuel pressure stays at 40. Can't replicate with wire wiggle test. O2 looks like it switches good, but always reads OPEN loop, I've read(for this truck) that it's ok if O2 switches.
      This happens twice during run cycle. First time is about 5 minutes after startup and lasts a couple of minutes. The second time is a couple of minutes later and lasts about 10 minutes then runs fine.
      You can hear an occasional stumble at idle, but very noticeable above idle.
      I saved some movies last night with the scanner and the scope. It looks like when coil fires it goes from +14v down to -14v, it don't look right to me, but I'm new at comparing waveforms. I think when this happens the ASD B+ drops to 10v.
      In the graphs my TPS don't seem to match RPM
      Does anyone know how to set dis. sync using scope and aligning cam and crank signals?
      Attached Files

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      • plus2
        Junior Member
        • Nov 2009
        • 26

        #4
        I cant upload the LSM scope file, I don't think it's too big it's 1039KB

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        • Papawrench
          Junior Member
          • Dec 2009
          • 17

          #5
          First have you checked coolant temp on scanner if o2 is switching but not going closed loop may be a thermostat stuck open.

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          • Crusty
            Senior Member
            • Dec 2007
            • 2450

            #6
            Some vehicles will go open loop at idle and back to closed loop shortly after you accelerate & pull away. Normal. Take a close look at the fuel trims. Lots of Dodges have a funky response to a "confused" O2 sensor signal.
            If the problem is there for 5 minutes & then 10 minutes, I don't think it's where the distributor is set. That should do it all the time, not some of the time. Make SURE of the rotor & cap quality though. Seen lots of junk secondary ignition parts on rebuilt distributors. Sounds like a fuel delivery issue as it warms up. Lean can create a higher demand on the secondary.

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            • plus2
              Junior Member
              • Nov 2009
              • 26

              #7
              I agree. My coolant sensor looks fine in the graph. It always stays in open loop, but O2 switches regularly . I'm leaning towards a PCM, I think the coil driver is bad, I'm not sure what else would drop coil voltage to -14v after firing. Also my MIL didn't come on when O2 was unplugged and scanner doesn't see dis. sync change when dis. is turned. Can't upload file LSM file. Any help uploading
              Last edited by plus2; 12-31-2009, 06:25 AM.

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              • Crusty
                Senior Member
                • Dec 2007
                • 2450

                #8
                Originally posted by plus2
                I agree. My coolant sensor looks fine in the graph. It always stays in open loop, but O2 switches regularly . I'm leaning towards a PCM, I think the coil driver is bad, I'm not sure what else would drop coil voltage to -14v after firing. Also my MIL didn't come on when O2 was unplugged and scanner doesn't see dis. sync change when dis. is turned. Can't upload file LSM file. Any help uploading
                Try to labscope the coil B+ voltage to VERIFY if it is in fact dropping, or is it just displaying that way on the scanner screen.
                The O2 sensor may need more time or more than i consecutive run cycle without seeing a voltage change. What dispalys on the scanner with it disconnected COULD BE a substituted calculated value.
                Try leaving the O2's disconnected and see if the condition is still there. Ignore the MIL light and the code sets for now. Just see if it happens when it reverts to base program. Don't forget to reset the fuel trims (record them first)

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                • plus2
                  Junior Member
                  • Nov 2009
                  • 26

                  #9
                  It still does it with O2 unpluged. I started a thread under lab scope, please read. Thank you

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