Mini Cooper Mssfire

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  • IDT7
    Member
    • Dec 2009
    • 75

    Mini Cooper Mssfire

    Hi,all
    I've got mini cooper 2008,1.6 N12 with valvetronic engine with missire on cyl 2 when engine is hot.There is no compression when it missfires,so I've scoped map sensor to see inlet manifold pulses .
    Top line is spark on cyl 1 and obviously erratic inlet manifold pressure but i need some help to interpret this waveform.
    Does the valve say shut,or does not open?
    Attached Files
    Last edited by IDT7; 12-24-2013, 01:47 AM. Reason: No image
  • Witsend
    Banned
    • Nov 2012
    • 2942

    #2
    Looking at red Trace (Map signal)

    I see a big dip on the red line at the point starting immediately after Cyl 4 is fired at TDC because Cylinder 2 intake valves start to open on the intake stroke with piston going down as cylinder 4 piston is going down on the power stroke.
    If a compression test or cylinder leakage test on cylinder 2 doesn't reveal any significant leakage on cylinder 2 , I would suspect sticking exhaust valve or weak valve springs, not seating exhaust valves

    Comment

    • crackerclicker
      Senior Member
      • May 2008
      • 400

      #3
      You have 3 intake pulls where there should be 4.

      Comment

      • IDT7
        Member
        • Dec 2009
        • 75

        #4
        This cylinder head had new inlet valves,exhaust valves,exhaust valve guides,and compression test which shows 0 compression when missfire occurs.
        Cylinder head specialists checked springs,valve heights etc. all ok.

        The reason why I posted it here is because i need more opinions on this waveform above.
        In my opinion intake valve cyl 2 does not open hence why there is no compression,no air taken in no air compressed.

        The symptoms:
        On cold engine start everything is ok every cylinder is firing
        After about 20 min cylinder 2 stops firing,carried out running compression test and shows 0 psi.
        The only way to get this cylinder running again is ti manually rotate valvetronic motor to higher valve lift.

        I've spent many hours on this problem,and got to the point where I know new cylinder head is the solution.At the moment I can't get one.
        Attached Files

        Comment

        • Witsend
          Banned
          • Nov 2012
          • 2942

          #5
          Cylinder 2 misfires hot

          I don't believe the valvetronic system disables any valves from opening or closing , but it can add or subtract from the amount of valve lift.
          I would get engine hot where you believe it looses compression and perform a cylinder leakage test on #2 with a cylinder leakage tester with low air pressure (cyl 2 at TDC of compression stroke)
          If full shop air pressure put in cylinder it might actually pop the hung open valve back closed and problem could be missed.
          Also if engine ever hydro locked and # 2 has lower compression , but acceptable leakage level , the piston might not be coming up as high in the cylinder if #2 rod is bent .

          Comment

          • crackerclicker
            Senior Member
            • May 2008
            • 400

            #6
            You sure you don't have an HVA leaking down when hot? Any ticking before it starts to misfire?

            Comment

            • IDT7
              Member
              • Dec 2009
              • 75

              #7
              Originally posted by Witsend
              I don't believe the valvetronic system disables any valves from opening or closing , but it can add or subtract from the amount of valve lift.
              I would get engine hot where you believe it looses compression and perform a cylinder leakage test on #2 with a cylinder leakage tester with low air pressure (cyl 2 at TDC of compression stroke)
              If full shop air pressure put in cylinder it might actually pop the hung open valve back closed and problem could be missed.
              Also if engine ever hydro locked and # 2 has lower compression , but acceptable leakage level , the piston might not be coming up as high in the cylinder if #2 rod is bent .
              Valvetronic can fully shut all valves,I've manually rotated eccentric shaft and it can be set to zero valve lift
              We have suspected cracked piston,removed it to inspect together with conrod no fault found
              Last edited by IDT7; 01-26-2014, 02:47 AM. Reason: More info

              Comment

              • IDT7
                Member
                • Dec 2009
                • 75

                #8
                Originally posted by crackerclicker
                You sure you don't have an HVA leaking down when hot? Any ticking before it starts to misfire?
                Crackerclicker , what is HVA tried to research it but not sure what it is?

                Comment

                • crackerclicker
                  Senior Member
                  • May 2008
                  • 400

                  #9
                  Hydraulic valve adjuster. They only use the HVA acronym in the training manuals, so I had to look it up to be sure too.

                  Admittedly, I don't know if a collapsed HVA would cause the valve not to open when Valvetronic is in low lift mode, but that seemed the most likely cause when you said you could get it to operate normally with full lift.

                  Comment

                  • Witsend
                    Banned
                    • Nov 2012
                    • 2942

                    #10
                    "Valvetronic can fully shut all valves,I've manually rotated eccentric shaft and it can be set to zero valve lift
                    We have suspected cracked piston,removed it to inspect together with conrod no fault found"

                    If it can open and fully close all valves , and you can manually rotate the ecentric shaft. The valvetronic sensor that appears to have a power supply section, a FS section (front Sense?), and a RS section (rear sense?). Maybe when engine gets hot one of the sensors or potentiometers or what's inside gets out of range that monitors the amount of valve lift?
                    KOEO hot, Can you manually rotate a known good cylinder's valve with the eccentric and take hot resistance readings on the sensor and compare it to the bad one full closed, mid open and , full open somehow. (of course you don't want a piston at TDC , if you are rotating eccentric to open valves.

                    Comment

                    • Witsend
                      Banned
                      • Nov 2012
                      • 2942

                      #11
                      So what was the verdict on the culprit there IDT7 ?

                      I figure if cylinder leakage good, hot oil pressure ok, I would watch this You tube Video. Sometimes good stuff on there and forums including folk dealing with similar problems and pattern failures. Let us know what you found.

                      Comment

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