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Mercruiser Mag MPI rough start.. Sometimes

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    Mercruiser Mag MPI rough start.. Sometimes

    Last Friday was concerned about a cloud of smoke that came from my engine bay and had asked someone who seemed knowledgeable about engines what would cause it. I had my engine running and he pulled the pvc valve to see if it was dirty and still had a vacuum.

    Looked clean to me, obviously it ran horrible for a minute but after he plugged the pvc back in I let it run for about 30 seconds before shutting it off. I came back hour or two later to start the engine and it would not want to start. It was turning over but was not firing. I had to throttle it a bit to get it fire up. I've never had this problem and the boat usually fires right up without any hesitation. Ran the boat this past weekend sat and sun never had any issues.

    Today after the boat had sat all week it fires right up. I took it for a quick spin, never got it over 30 and probably didn't run it more than but 2-5 minutes. I docked it at the ramp, fiddled around for 30 minutes and came back to start. Same thing except it wouldn't let me throttle any to get it started. It would just stop cranking when I did. I tried probably 4-5 times and on the last one I let it crank for about 10 sec. I could hear fumbling to start so I gave it a little throttle and it started up. I took it for another quick spin to make sure it was running ok, everything seemed fine.

    My research points this to iac valve... Is it just coincidence that that the iac is acting up after the guy was messing with pvc valve?! Surely the pvc valve wouldn't cause this?

    #2
    It could be possible it is vapor lock? The ethanol in the fuel can vaporize at a lower temp. Maybe you just got a bad tank of fuel?
    Where are you located and how hot was it?
    Mike Allen, Tigé owner since 1997

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      #3
      South Carolina, been in the 100s and humid


      Sent from my iPhone using Tapatalk

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        #4
        Mercruiser Mag MPI rough start.. Sometimes

        I usually fill up at the Spinx gas station with "Purmax" ethanol free gas. 1 time I did fill up with 93 octane that probably had ethanol but that was months ago and I used stabilize marine additive. This had happened twice; once filled up with Spinx Puremax fuel and recently with supposedly ethanol free marina fuel.

        What can I do to prevent the vapor lock? Let engine sit longer? Open sun deck? There was times during the weekend I shut off engine and within 15 min turned back on no problem but that was out in the middle of the lake. Seemed like both times this issue occurred was sitting at the dock and not being ran for longer than 10 min.
        Last edited by jamesbond; 07-08-2016, 04:02 AM.

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          #5
          IF it is vapor lock there are a few things that you can do to help minimize the effects. I am no expert and it could end up being something else? To permanently fix vapor lock from re-ocurring is to install a new secondary fuel pump.

          When it is hot that worsens a vapor lock problem. If there is a way you can check your fuel pressure that might help you troubleshoot some more.

          I will see if I can find some of the old threads tomorrow.
          Mike Allen, Tigé owner since 1997

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            #6
            http://www.tigeowners.com/forum/show...r-Sensor-issue
            http://www.tigeowners.com/forum/show...-problem-HELP-!!!
            http://www.boatfix.com/merc/Bullet/99/99_07.pdf
            Mike Allen, Tigé owner since 1997

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