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    Engine Surging After Heating Up.

    Hi all. I am running out of solutions and could use some thoughts or ideas. We recently purchased a 1990 Cierra 2556 with a 5.7 liter Mercruiser. When we took it out for the first time, it ran good for about an hour and then the engine started surging (dropping rpm and then coming back up). We were able to drop the rpm to about 2800 and everything seemed fine, but could not speed up without it surging again. The next time we took it out, the same thing happened. It appears like it runs fine at higher rpms when it is cold, but once it warms up, it starts surging. I have searched the forums for solutions and have methodically replaced the following:

    1. Fuel Filter (Although it was not noticeably dirty)
    2. Spark Plugs and Spark Plug Wires
    3. Distributer Cap and Rotor
    4. Ignition Sensor
    5. Coil

    Although the boat is running significantly better and more efficiently after replacing all those items, we still have the same issue; only it now happens after about 15 minutes on the water.

    Has anyone experienced this and found the ultimate solution. Most of the forum posts here and elsewhere described a similar problem, but then never identified what actually solved it.

    Thanks for your help in advance!



    #2
    Is the 5.7L a repower? Carburetor or MPI? Do you know approximately how many hours it has? It almost sounds like a possible vapor lock situation where the fuel pump is inadequately getting fuel to the engine once it warms up.
    Jeff Prime
    "Optimystic Prime"
    2000 Bayliner 2855 Ciera Sunbridge
    Anacortes, WA

    Comment


    • hhergett
      hhergett commented
      Editing a comment
      Hi optimist_prime. As far as I know it is not a repower. It has approximately 500 hours on the engine and is a carburetor. I have wondered about a vapor lock, but have no idea how to track that down.

    #3
    Have you tried it with the fuel cap loose ?
    A clogged tank vent can cause issues like that.
    " WET EVER "
    1989 2459 TROPHY OFFSHORE 5.8L COBRA / SX
    mmsi 338108404
    mmsi 338124956
    "I started with nothing and still have most of it left"

    Comment


    • hhergett
      hhergett commented
      Editing a comment
      Hi dktool. Yes, I did try it with the fuel cap loose. No change

    #4
    Originally posted by dktool View Post
    Have you tried it with the fuel cap loose ?
    A clogged tank vent can cause issues like that.
    But wouldn't a clogged fuel vent cause the symptom to happen before it's warmed up as well?
    Jeff Prime
    "Optimystic Prime"
    2000 Bayliner 2855 Ciera Sunbridge
    Anacortes, WA

    Comment


      #5
      Originally posted by optimist_prime View Post

      But wouldn't a clogged fuel vent cause the symptom to happen before it's warmed up as well?
      Depending on how long it takes the tank to pull into a vacuum. Fuel level will effect that also.

      When it starts to surge, loosen the cap and see if the condition changes,
      " WET EVER "
      1989 2459 TROPHY OFFSHORE 5.8L COBRA / SX
      mmsi 338108404
      mmsi 338124956
      "I started with nothing and still have most of it left"

      Comment


      • builderdude
        builderdude commented
        Editing a comment
        I agree

      #6
      Originally posted by optimist_prime View Post

      But wouldn't a clogged fuel vent cause the symptom to happen before it's warmed up as well?
      Regarding a plugged fuel vent: typically the boat runs great at cruising rpm for a certain amount of time then starts to fall on its face. Might even run all day long at low rpm.
      I agree with dk to remove the fuel cap next time it happens to see if that’s the issue.
      Dave
      Edmonds, WA
      "THE FIX" '93 2556
      Carbureted 383 Vortec-Bravo II
      The Rebuild Of My 2556 https://www.baylinerownersclub.org/f...76?view=thread
      My Misc. Projects
      https://www.baylinerownersclub.org/f...56-gctid789773

      Comment


      • hhergett
        hhergett commented
        Editing a comment
        Thanks builderdude. I should have mentioned that in my original post, as I had seen that in other posts concerning this issue and tried that. No difference.

      #7
      I had a similar experience once, replaced fuel pump, carb and other tune up items. Finally found the issue...it ended up being debris on the fuel pickup in the tank..
      Brad & Michelle
      Jet & Maverick
      1993 3688 "the Kraken"
      Hino W06 250HP
      14' Avon RIB, 50hp Tohatsu
      Moored at Shelter Bay
      LaConner, WA

      Comment


      • hhergett
        hhergett commented
        Editing a comment
        Thanks Dirtyface. How big of a job was it to get to that?

      #8
      Your fuel tank pickup tube is part of the fitting that threads into the tank, it’s located at the aft end of the fuel tank (follow your fuel line). Should be fairly easy to access. Remove the fuel line and unthread the fitting from the tank and remove, there’s a screen on the bottom end.
      Dave
      Edmonds, WA
      "THE FIX" '93 2556
      Carbureted 383 Vortec-Bravo II
      The Rebuild Of My 2556 https://www.baylinerownersclub.org/f...76?view=thread
      My Misc. Projects
      https://www.baylinerownersclub.org/f...56-gctid789773

      Comment


      • hhergett
        hhergett commented
        Editing a comment
        Thank you

      • hhergett
        hhergett commented
        Editing a comment
        Following up on this for the solution. I let this go for a while as the king salmon fishing was good here in Juneau, AK and the boat trolled just fine. Took a bit to get there, but it is all fun on the water! Had a down day and took your advice to pull the fuel line pickup tube. Was not that hard to get at and came out pretty easy. The pickup tube and ant siphon valve attached to it seemed fine, but I gave them a thorough cleaning anyway. What I discovered as I was doing that piece, was that there was another inline fuel filter installed in the fuel line near the gas tank. That fuel filter was obviously plugged. Since there was not a similar fuel filter in town, I bought a section of fuel line hose and ran it directly from the fuel tank to the water separator. Not entirely sure why there is another inline filter since there is a filter at the carb, but it fixed the problem. Took the boat out for a 2 hour cruise yesterday and it ran great! Thank you again for your advice.

      #9
      Your thread title mentions; Surging after Heating up! Define "heating up".
      Are you talking about reaching operating temperature, or as in over-heating?



      Good advice regarding the fuel tank pick-up tube/screen.
      As Dave suggested, it is very easy to remove, check and clean.


      Click image for larger version  Name:	fuel tank pick up tube and screen.jpg Views:	0 Size:	57.9 KB ID:	648927


      Here's my take on what I believe is a partial Myth regarding a clogged fuel tank vent hose (or vent fitting) and the result of prevent the fuel pump's ability to pull from the fuel tank, and to supply fuel to the engine!

      I've created two scenarios here.
      One with a full tank, and one with a half full tank.

      The fuel pump must be able to create an approximate 1.0" to 1.5" Hg to get past the Anti-Siphon valve.
      If the pick-up tube screen is restricting flow, this value would likely be increased!

      One gallon of gasoline = 231 cubic inches of volume.

      If we burn one gallon of fuel, that means that 231 cubic inches of air space has been added to the blue area.
      If there is no make up air (as in what a clogged vent line would cause), that 231 cubic inches creates Negative pressure.
      Therefor causing the need for the fuel pump to produce more negative pressure (vacuum).

      In scenario A, with very little air space above the fuel level, it becomes obvious that the absence of one gallon may have an effect.
      In scenario B, with much more air space above the fuel level, it becomes obvious that the absence of one gallon may not cause as great an effect!

      Bottom line, before blaming a clogged vent line, consider the amount of fuel in the tank, and how much fuel is being consumed before the issue occurs!
      I'm not suggesting that a clogged vent will NOT cause issues, I'm simply suggesting that in scenario B, in may not, or it may take longer to appear.


      Click image for larger version

Name:	fuel tank clogged vent line explained.jpg
Views:	56
Size:	119.8 KB
ID:	648930


      A simple test would be to install a very sensitive high quality vacuum gauge into the fuel filter base unit.
      This one includes a tattle-tale needle.


      Click image for larger version  Name:	Fuel filter base vacuum gauge.jpg Views:	0 Size:	53.0 KB ID:	648929

      Several more things worth mentioning:

      Have you verified that you are propped correctly, and are able to achieve your OEM suggested WOT RPM?
      If you are over-propped, you will over-burden your engine at all RPM.

      Have you looked at both your Progressive and Total Ignition advance?

      You have a GM SBC that has been Marinized.
      The Marine version of this engine is fitted with the GM Full Dished pistons.
      This piston profile makes this engine more prone to Detonation if the Progressive and TA are too aggressive.

      Detonation can cause several different types of issues, the worst being piston damage.
      It can also cause some ignition systems to bump the spark lead back, which will cause a loss of power.

      Find your OEM ignition advance curve, and then check your Progressive and Total spark advance dynamically.




      .
      Rick E. (aka RicardoMarine) 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

      Please, no PMs. Ask your questions on forum.

      Comment


        #10
        Following up on this for the solution. I let this go for a while as the king salmon fishing was good here in Juneau, AK and the boat trolled just fine. Had a down day and took Dirtyface's advice to pull the fuel line pickup tube. Was not that hard to get at and came out pretty easy. The pickup tube and ant siphon valve attached to it seemed fine, but I gave them a thorough cleaning anyway. What I discovered as I was doing that piece, was that there was another inline fuel filter installed in the fuel line near the gas tank. That fuel filter was obviously plugged. Since there was not a similar fuel filter in town, I bought a section of fuel line hose and ran it directly from the fuel tank to the water separator. Not entirely sure why there is another inline filter since there is a filter at the carb, but it fixed the problem. Took the boat out for a 2 hour cruise yesterday and it ran great!

        Comment


          #11
          The engine mounted fuel filter water separator should be all you’d need. Somebody likely added that additional in line.
          FWIW: Parker Racor has a filter that’ll spin on to the OEM filter housing.
          Dave
          Edmonds, WA
          "THE FIX" '93 2556
          Carbureted 383 Vortec-Bravo II
          The Rebuild Of My 2556 https://www.baylinerownersclub.org/f...76?view=thread
          My Misc. Projects
          https://www.baylinerownersclub.org/f...56-gctid789773

          Comment

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