Port engine popping problems

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by LadyLauraIV, Dec 2, 2021.

  1. LadyLauraIV

    LadyLauraIV New Member

    20
    Nov 7, 2021
    ft pierce fl.
    2002 340 Amberjack 8.1L Raymarine elect.
    8.1L Mercruisers inboard
    02 340 AJ 8.1 inboards. 393 hrs. we bought the boat from someone who neglected it.
    during sea trial port engine would not get above 3000 rpm and popping thru intake.
    indicating to me a lean backfire, the marina owners told me this boat hadnt been taken out in at least a year. it had 3/4 full tanks. i checked fuel pressure at idle and it gave me 36 psi.
    so i changed both boost pump and hi pressure pump, coolers, regulators and fuel/water separators in the cf2 system on both motors (im sick that way) took it out and got better power but port side was firewalled at 3600 rpm with some occasional popping, but not as much. while starboard side was a little past halfway at 3600 rpm. we used as much of the old fuel as possible got down to around 1/4 tanks and filled up at our marina. then took it out and had a improvement in power but still popping and throttles still spread. we had very little issues until we turned around to go back, i powered up and got a ton of popping around 3400 rpm out of port motor. got back to the slip and put on the diacom system- no fault codes.
    went to the test section and did a induced misfire test at 1600+/- 50rpm and #5 cyl showed no change. pulled plug an found porcelain was white on one side and dark on the other side. did compression test it was 172psi to 180 in all cyl with #5 being 180psi. replaced plug then tested injector pulse at idle no problem there. coil firing nice at idle.
    i'm taking her out sat for a full load test with fuel pressure gauge and diacom setup. can anyone think of anything else that i might have missed? Thanks in advance for your input.
     
    BillK2632 likes this.
  2. techmitch

    techmitch Well-Known Member PLATINUM Sponsor

    May 1, 2008
    Chesapeake Bay, Middle River/Frog Mortar Creek MD.
    1999 270 DA
    Twin 4.3s W/Alpa I Gen II's
    I would start with all new plugs and wires even if fuel pressure checks well. Could be fouled injectors also.
     
    Nater Potater, scoflaw and Shaps like this.
  3. Little Ducky

    Little Ducky Well-Known Member

    Jun 5, 2017
    Dickson, TN / Chattanooga, TN
    1998 290 Sundancer
    Twin EFI 5.0L w/Alphas
    Kohler 4kW
    Have you checked the timing?

    I only got popping out of my old VW when the timing was off.
     
  4. LadyLauraIV

    LadyLauraIV New Member

    20
    Nov 7, 2021
    ft pierce fl.
    2002 340 Amberjack 8.1L Raymarine elect.
    8.1L Mercruisers inboard
    actually i checked the spark advance and it was swinging from a high of 9 deg adv. to -15 deg
     
    Little Ducky likes this.
  5. LadyLauraIV

    LadyLauraIV New Member

    20
    Nov 7, 2021
    ft pierce fl.
    2002 340 Amberjack 8.1L Raymarine elect.
    8.1L Mercruisers inboard
    thanks Mitch i was pretty much headed in that direction the weird thing is i never got so much as a hiccup from the starboard side engine.
     
  6. techmitch

    techmitch Well-Known Member PLATINUM Sponsor

    May 1, 2008
    Chesapeake Bay, Middle River/Frog Mortar Creek MD.
    1999 270 DA
    Twin 4.3s W/Alpa I Gen II's
    Do them both. Get yourself a good baseline since the boat is new to you.
    Also with the way it's running, oil changes may be in order if they haven't been done recently or are now contaminated.
     
  7. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Start there and if that doesn't do it check your fuel pressure when your engine hits the wall. Is that a 3 or 4 bar fuel system.?
     
  8. Nater Potater

    Nater Potater Well-Known Member GOLD Sponsor

    864
    Oct 19, 2020
    Southwest Idaho
    1992 300DA Sundancer
    Twin Merc Alpha Gen II I/O's with 5.7 V8's
    A high of 9 degrees BTDC? Was that at idle? Make sure you're getting somewhere around 34 degrees BTDC when at cruise rpm. You have a great advantage in your troubleshooting regimen as there's a good running engine right next to it for comparison.
     
    Little Ducky likes this.
  9. Little Ducky

    Little Ducky Well-Known Member

    Jun 5, 2017
    Dickson, TN / Chattanooga, TN
    1998 290 Sundancer
    Twin EFI 5.0L w/Alphas
    Kohler 4kW
    I'd swap out some ignition parts from your running motor to the one having issues to find the problem.

    Sounds like your a good DIY'er..... so while trying to trouble shoot don't toss to many new parts at it until you pin point the problem.
     
    Nater Potater likes this.
  10. LadyLauraIV

    LadyLauraIV New Member

    20
    Nov 7, 2021
    ft pierce fl.
    2002 340 Amberjack 8.1L Raymarine elect.
    8.1L Mercruisers inboard
    4 bar
     
  11. LadyLauraIV

    LadyLauraIV New Member

    20
    Nov 7, 2021
    ft pierce fl.
    2002 340 Amberjack 8.1L Raymarine elect.
    8.1L Mercruisers inboard
    i'm not a proponent of switching parts from one engine to another
    lofs done twice since ive owned her (2 months)
     
  12. LadyLauraIV

    LadyLauraIV New Member

    20
    Nov 7, 2021
    ft pierce fl.
    2002 340 Amberjack 8.1L Raymarine elect.
    8.1L Mercruisers inboard
     
  13. LadyLauraIV

    LadyLauraIV New Member

    20
    Nov 7, 2021
    ft pierce fl.
    2002 340 Amberjack 8.1L Raymarine elect.
    8.1L Mercruisers inboard
    it wasntconstant, that was just the peak advance at idle
     
  14. techmitch

    techmitch Well-Known Member PLATINUM Sponsor

    May 1, 2008
    Chesapeake Bay, Middle River/Frog Mortar Creek MD.
    1999 270 DA
    Twin 4.3s W/Alpa I Gen II's
    lofs, I know where that comes from.
     
  15. mrsrobinson

    mrsrobinson Well-Known Member SILVER Sponsor

    Mar 9, 2006
    USA
    N/A
    N/A
  16. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    4 bar should be 42#'s
     
  17. Spark600

    Spark600 Active Member GOLD Sponsor

    344
    Dec 28, 2013
    South Shore Long Island NY
    2015 Sundancer 410
    Onan Generator
    Mercury dinghy
    Cummins QSB HO 380 HP
    Zeus Pods
    Was the gas treated before it sat for a year
    Maybe bad gas
     
    Last edited: Dec 3, 2021
    mrsrobinson likes this.
  18. Nater Potater

    Nater Potater Well-Known Member GOLD Sponsor

    864
    Oct 19, 2020
    Southwest Idaho
    1992 300DA Sundancer
    Twin Merc Alpha Gen II I/O's with 5.7 V8's
    Understood, but you should be more interested in what the advance is doing in the rpm band where you're having trouble. That's why I suggested checking the timing up around 3000-3400 rpm. The reason you see the idle timing move around is due to the idle stabilization circuit that's written into the ignition control box.
     
  19. Pirate Lady

    Pirate Lady Well-Known Member

    Jun 2, 2020
    Middle River, Chesapeake
    Pirate Lady
    1991 250 Sundancer
    MMSI 338377928
    7.4 carb, Bravo 1
    Where you learn this stuff? Seriously.
     
  20. Nater Potater

    Nater Potater Well-Known Member GOLD Sponsor

    864
    Oct 19, 2020
    Southwest Idaho
    1992 300DA Sundancer
    Twin Merc Alpha Gen II I/O's with 5.7 V8's
    What part?
     

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