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any mechanics out there! my 3.0 deisleing under load?-gctid416682

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    any mechanics out there! my 3.0 deisleing under load?-gctid416682

    i have a 1985 omc 3.0 which came stock on my 21.8 ft 2160 trophy hard top. when crusing and hit rough current in ocean it may knock me off plane and boat works hard to get back on plane it deisles like a valve chatter? i did have crap gas like ten gallons but i drained tank .since put new gas some octane booster and stabil in fuel. when i retard timing seems to help it get better. .should i retard timming a little more? dont want to damage motor it runs great . but this boat came under powered so maybe after all these years took toll on engine ? so under load chatters? fine on a lake or were no turbulant waves and current occur but i am an ocean boy so i would like to try and inprove it even if just a little. any suggestions?

    #2
    OK.... dieseling and run-on are generally thought of as one in the same. This occurs when the ignition power is cut on a rather warm engine, and the lean fuel/air mixture allows it to continue running.

    Perhaps what you are describing is detonation, since this is occuring while under power.

    In 1985, your ignition system is likely using mechanicl advancement (i.e., flyweights and return spring mechanism).

    If the flyweight return springs have become compromised, yet the flyweights are free, your advancement may be running wild (i.e., too early/too great).

    You'd best throw a timing ligt on this, and see what the progressive spark advance is doing against your OEM specs.

    Not BASE advance...... BASE will remain the same. We're talking about the progressive and TA ... total advance.

    If the progressive is coming on too strong/too early, your cylinders may be detonating under load.

    Pull the cap, remove the breaker plate, and examine the flyweights and return springs.

    Look for rusty return springs that have lost their spring tension value.

    Post back, and I'll make a suggestion as to correct this.

    .
    Rick E. Gresham, Oregon
    2850 Bounty Sedan Flybridge model
    Twin 280 HP 5.7's w/ Closed Cooling
    Volvo Penta DuoProp Drives
    Kohler 4 CZ Gen Set

    Comment


      #3
      Detonation can cause major damage real fast.

      I think we discussed TA with you before and you checked it.

      Changing your timing in the dark is not a good idea. Use a light, get it to specs at base and then check to see what it does when it is supposed to advance. Make sure the springs and weights move freely. WD40 down there is ok. It sounds like it might be sticky and not returning to base quickly enough when rpm's drop. Either broken springs or sticky mechanism.

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        #4
        i already had one bad distributor. the weights were hitting side of housing. i replaced with one i had from my other boat which was the same motor. i will check that out it could also be a problem as well. thanks i will let you know

        Comment


          #5
          can you put new springs or is it a distributor change?

          Comment


            #6
            Whats the plugs look like.

            http://www.ngksparkplugs.com/tech_su...qs/faqread.asp

            Compression is what ?

            And yes i agree underpowered i have the 140 / 3.0 l in my 19' Better then the 2.5l that the boat came with but how i wish i had the 4.3l in it.

            What prop you have on ?
            Be good, be happy, for tomorrow is promised to no man !

            1994 2452, 5.0l, Alpha gen. 2 drive. Sold ! Sold ! Sold !

            '86 / 19' Citation cuddy, Merc. 3.0L / 140 hp 86' , stringer drive. Sold ! Sold ! Sold !

            Manalapan N.J

            Comment


              #7
              Funny thing this thread reminded me of what happened this summer. I live around 2000ft above sea level so I'm thinking this was probably the cause. When I went down to sea level this year my boat motor 5L LX started dieseling when I shut it off after running a bit but at 165-170* which is very normal for my boat. Other than that it run perfect. The second day out I started to trouble shoot. I looked down at my tach and noticed my idle rpm had climbed up approx 120 rpm. I know this is not much as my idle speed was now around 725-780. I turned down the idle to 600 dead on and that was the end of my dieseling problem immediately even when the engine was warm. It really amazes me how touchy a marine engine can be at different altitudes.

              Good luck with yours.

              Comment


                #8
                i had my compression checked out and it was good i think around 120 to 130.my boat and this underpowered motor came with a 13.3/4 inch by 15 pitch prop. that is what bayliner has on there old records. noy a very fast boat but a nice comfotable ride.i put another distributor in her going to test today.if still an issue i will get a brand new one i had two kicking around and the one that was in it was in my 19 ft bow rider and it used to ping to under load just not as bad so it makes sense that distributor spent 15 years every sat and sunday off the coast of maine fishing and inside dist was pretty rusty .almost time to winterize here in the north east but gonna get a few more weeks out fishing the return migration of striped bass . you can e mail bayliner and they can tell you all the modles that came out of your boat and the motors and props they came with. they also told me there bimini top buiss was sold to a company in washington state and they have specs and matirial for all the bayliner biminis from 2006 and earlier. my 2160 came with hard top and bimini that snaps under top and has zip in sides that enclosethe whole boat like a camper.

                Comment


                  #9
                  striper.com wrote:
                  ... i put another distributor in her going to test today. if still an issue i will get a brand new one ................ so it makes sense that distributor spent 15 years every sat and sunday off the coast of maine fishing and inside dist was pretty rusty
                  Please take this the right way........

                  but when these issues come up, we're far better off to check and see just what the ignition advance was doing BEFORE we remove the existing ignition distributor. rod

                  You have now missed your oportunity to see what the old one was doing!

                  This leaves us with a disadvantage if there were any concerns regarding the original issue.

                  Before you haphazardly jump the gun here with yet another used and potentially tired ignition distributor, at least set your base advance, and take a further look at your progressive and TA.

                  For any of us who end up tearing our engines down due to major damage, if at all possible run it and look at your progressive advance while you still have the chance to.

                  Once you remove the ignition distributor....., that chance is gone!

                  .
                  Rick E. Gresham, Oregon
                  2850 Bounty Sedan Flybridge model
                  Twin 280 HP 5.7's w/ Closed Cooling
                  Volvo Penta DuoProp Drives
                  Kohler 4 CZ Gen Set

                  Comment


                    #10
                    In my old 87 2150 Capri cuddy with a 3.0, I always used this stuff if I couldn't find Sunoco 94 fuel. It kept the knock and ping at bay.



                    otherwise, it sounded like someone was playing the spoons in the bilge...

                    Comment


                      #11
                      I researched these 3.0's alot when I was looking at getting a boat, and wasn't really impressed knowing what I know about motors.

                      The exhaust and intake manifold are a common casting, making for a potentially warm air intake temp into a U-flow cast iron pushrod head. Similar to the SBC 400, these like to develop cracks between cylinders in the heads and in more rare events even the block. They do not dissipate heat well and that is why you'll see numerous posts on here with problems about run on and pinging, some having to go to premuim fuel or add octane booster.

                      Merc tried to increase the 3.0's performance and started blowing them up, again in my opinion the U-flow head is a poor design and is prone to detonation which is probably what killed the hopped up test motors.

                      A much more reliable and powerful engine could be had if they would go to basically half a 350(no siamese cylinders) with an aluminum head, and run the intake and exhaust out opposing sides. The motor would use a small block head and one manifold, the same parts that fit all the SBC's so parts would interchange and be easy to get....but I'm just a average joe not a GM engineer so I'll get off my podium... Enough of my rant...

                      Be careful with that pinging/run on, check your timing curve and try premium fuel. You don't want to be miles out in the ocean with a hole in a piston.

                      Comment


                        #12
                        the one that was pinging came from my old boat and it did the same thing in that boat just not as bad due to not as much of a load on motor. i dont care what the total advance is it should work if not, it is no good .base time should be all i need. the anvance should be automatic if distributor is good ? if not there is a problem with either distributor or fuel. i drained all old fuel cleaned tank so that is not the issue it is the distributor so i got a new one timed and it is ok i did not need to disect why i will not fix it i just got brand new one and solved the issue . just want to thank everyone for there great advise it led me to the problem directly some times you over think or over look some obvious things and others help get you back on track. i especially want to thank 2850 bounty and trophy boat for all your great advise thank alot hope i can return the favor!

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