Grumbling noise while on plane and then fuel smell

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by Capt.Will, Jul 7, 2020.

  1. Capt.Will

    Capt.Will Member

    77
    Aug 15, 2016
    Lake St. Clair
    1997 Sea Ray 330 Sundancer
    7.4 MPI Mercruiser Inboards
    Vessel: 1997 330 Sundancer

    Engines: 7.4 L Mercruiser MPI inboards (V drives)

    Issue: STD engine intermittently will produce a noise that sounds almost like it has lost a cylinder or two while on plane. Usually in rough water not smooth water conditions. Performance doesn't really change. Whenever this noise happens I then come off plane and will smell fuel in the exhaust. There is no evidence of fuel in the bilge/engine compartment.

    Saturday when this happened I waited about 2 hrs before starting the engine again and white/blue smoke was produced momentarily out the exhaust after start up. Could I be loosing a cylinder or do you think this is something else?

    Recent preventative maintenance: New spark plugs/cap/rotor. Refinished props. New fuel filter/water sep. Recently hooked up scan tool and no codes show up. Timing, temperature and everything else checks out A-OK.

    Any help here would be great.
     
  2. Capt.Will

    Capt.Will Member

    77
    Aug 15, 2016
    Lake St. Clair
    1997 Sea Ray 330 Sundancer
    7.4 MPI Mercruiser Inboards
    After a friend recommended to check all the engine ground posts I did find some minor corrosion on two so I removed all posts and wires. Cleaned them up and properly reattached them. Seemed fine for one run. Second and Third run yesterday I now have blue smoke and decent amount of fuel exiting exhaust. I am trying to schedule a mechanic now but having a tough time with that. Any suggestions at this point would be much appreciated. William
     
  3. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Put a gauge on your fuel rail, see if it has the correct psi. See how quickly it leaks down after shut off, could be stuck injector or 2.
     
    Capt.Will likes this.
  4. Capt.Will

    Capt.Will Member

    77
    Aug 15, 2016
    Lake St. Clair
    1997 Sea Ray 330 Sundancer
    7.4 MPI Mercruiser Inboards
    Injectors were recently cleaned by Kinsler Injectors in Troy, MI. I also recently replaced the low pressure fuel pump.
     
  5. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Maybe a dead cylinder or 2. Could be sky high fuel pressure.
     
  6. Capt.Will

    Capt.Will Member

    77
    Aug 15, 2016
    Lake St. Clair
    1997 Sea Ray 330 Sundancer
    7.4 MPI Mercruiser Inboards
    Finally a solution has presented itself. When I replaced the plenum the last time I misplaced the OEM vacuum tube that connects the fuel regulator to the plenum so I replaced it with a tube that obviously did not do the job it should have. I since found the OEM vacuum tube and installed it and now there is no smoke or raw fuel exiting exhaust.

    So after that issue was solved, the idle RPM was too high. About 1100 RPM. I removed the plenum once again and removed the IAC motor to find it gummed up and extended too far out. Replaced that ($140) and the engine is purring like a kitten and all functions normal.

    Thankfully I am willing to take a shot at these issues myself because NOT ONE mechanic in this area will return a phone call or email. NOT ONE!!
     

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