Engine Start Problems

Discussion in 'General Discussion' started by Flytrade, Feb 19, 2020.

  1. Flytrade

    Flytrade Member

    175
    Feb 20, 2018
    Bradenton, FL
    2006 320 Sundancer
    Twin 6.2L Mercruiser
    When my 6.2L Mercruiser port engine is cold it starts fine. Turn on the engine, wait about 5-10 seconds for the fuel pump to pressurize the system, and then hit the start button with the throttle at idle. It starts, idles and runs fine at all rpm's.
    When the engine is warm - has been shut down within the past couple of hours - it's hard to start, or may not start at all. I use the same technique as above, and the engine turns over and sounds like it's going to start, but when I let go of the start button the engine dies. I then try moving he throttle to various positions, and sometimes I can get it to start, and sometimes it wont.
    I had my mechanic install all new spark plugs, wiring harness and distributor cap. I still have the same problem.
    Any thoughts would be appreciated.
     
  2. Korkie

    Korkie Active Member GOLD Sponsor

    715
    Feb 2, 2016
    Leonardtown, MD Potomac River / Chesapeake Bay
    340 Sundancer 2006, Garmin 7612, xHD Radome
    Merc 496 Mags
    Bravo III Drives
    Vapor Lock ?
     
    370Dancer likes this.
  3. Captn TJ

    Captn TJ Active Member

    872
    Sep 19, 2017
    Catawba Island, Oh
    2005 280DA
    Raymarine E80
    5.0 with Bravo 3
    IAC Valve?
     
  4. Lazy Daze

    Lazy Daze Well-Known Member TECHNICAL Contributor GOLD Sponsor

    Apr 21, 2009
    PA
    Various
    Various
    Agree with Cap, above... A good first thing to try is to advance the throttle at least 1/3. If that works, it's most likely the IAC. And, this would probably be the most common reason. You could also swap the IAC from port to stbd to see if the problem follows.
     
  5. Captn TJ

    Captn TJ Active Member

    872
    Sep 19, 2017
    Catawba Island, Oh
    2005 280DA
    Raymarine E80
    5.0 with Bravo 3
    I always carry a spare IAC in my kit. Pretty easy/quick change out.
     
    OllieC likes this.
  6. dvx216

    dvx216 Well-Known Member SILVER Sponsor

    Feb 1, 2012
    Catawaba Island,Oh.
    2000 310 sundancer 5.7
    optional electronic package






















    n/a
    twin 5.7 300 Hp.
    Start with what you don't know check and see if you have a good spark if you do find out what your fuel pressure is on the fuel rail.
     
  7. Shenanigans77

    Shenanigans77 Member GOLD Sponsor

    50
    Feb 17, 2020
    Lk St. Clair
    2003 320 Sundancer
    Twin 6.2 Mercruiser Bravo III
    I've been down this road as I have a pair of 6.2s myself. Should have 42psi at the rail with the fuel pump running. I would also do a compression test to rule out weak cylinders. I had low compression in two cylinders due to a blown headgasket between the cylinders. I had the same problem that if the motor didn't start right away when it was warm then it was almost impossible to start, started cold just fine.

    Try this as well. Next time you take her out and shut her down, before you attempt a warm restart, advance the throttle slightly. Then return it to idle just as she fires up.
     
  8. Flytrade

    Flytrade Member

    175
    Feb 20, 2018
    Bradenton, FL
    2006 320 Sundancer
    Twin 6.2L Mercruiser
    As per your suggestions above, I had the IAC and fuel pressure tested, and they are normal.
    We could not duplicate the condition at my dock - I suspect the engines need to be run at normal speed and temp for a while.
    I did take the boat our for a run, but turned on the blower for about 5 minutes before shutting down the engines. This seemed to solve the problem.
    I was also told the problem could be with the fuel blend. It seems the blend is changed depending on use for summer or winter. I could have a winter blend - which is more volatile - but it could be causing a vapor lock because I live in Florida and we are having a warm winter.
    In any case, I would like to thank everyone for your help.
     
  9. dan313

    dan313 Member

    174
    Sep 27, 2009
    Long Island
    2005 270 Amberjack
    350 Mag Bravo3
    I've been chasing this same problem for a few years now. This is what has been done to my motor.
    The Gen3 fuel pump, injectors, numerous IAC valves, TPS sensor, Distributor cap and rotor all have been replaced. I still have the issue. It comes and goes. Sometimes the engine starts right up. Other times I have to advance the throttle. If you can figure it out. Please let me know.
    Thanks
     
  10. hottoddie

    hottoddie Well-Known Member

    Jan 11, 2012
    Boston/Cape Cod
    1986 Sea Ray 390 EC
    Garmin 4212 Chartplotter
    Garmin 24 HD Radar
    Garmin 546s Plotter
    454 Crusaders
    I have seen several boats with Mercruiser MPI engines over the last several years that have intermittent start/stall/lack of power etc. Mechanics chase these with computers and can't find anything wrong. Quite often the problem turn out to be a faulty fuel pump relay causing fluctuating or complete loss of fuel pressure. These relays are cheap and easy to swap out. Not a bad idea to keep a spare onboard.
     
  11. ExumaBlue

    ExumaBlue New Member

    25
    Nov 19, 2019
    2003 290 BR
    Twin 350 MAG MPI 5.7L w/Bravo I
    Do you have a part # for the relay? I'm having the same issue and will try to swap one out. Thanks.
     
  12. hottoddie

    hottoddie Well-Known Member

    Jan 11, 2012
    Boston/Cape Cod
    1986 Sea Ray 390 EC
    Garmin 4212 Chartplotter
    Garmin 24 HD Radar
    Garmin 546s Plotter
    454 Crusaders
    No I don't have a part# as my boat does not use these relays. I have 2 friends with MPI Sea Rays that have had the issue and keep them onboard but won't see them for awile.
     
  13. Craig

    Craig Well-Known Member GOLD Sponsor

    740
    Feb 8, 2007
    Maryland
    2006 320 Sundancer
    twin 350 Horizon V drives
    Seems like its always the 6.2's with this issue. I've seen a few folks that have chased this. Seems like the 5.7's are not as prone. Anyone else seeing this.
     
  14. Wanderer 290

    Wanderer 290 Active Member

    162
    Jul 1, 2019
    01 sea ray 290 sundancer
    Twin 5.7 b3’s
    Since you have twins try swapping the fuel pump relays and see if the problem follows?
    If the problem continues follow the protocol of swapping one component at a time until the problem follows?
     
  15. Ovmman

    Ovmman Member

    45
    Sep 16, 2016
    Great South Bay, Long Island
    2005 280 Sundancer with twin 4.3 engines, alpha 1 gen 2
    Twin 4.3 alpha 1 gen 2
    Hey guys, been chasing this problem since the day I bought the boat, this,that and the other thing, after 6 years I finally gave up and just start the boat at half throttle. Works every time
     
  16. OllieC

    OllieC Well-Known Member SILVER Sponsor

    Mar 11, 2013
    MinniSoCold
    Sara Belle
    2005 Weekender 215
    Mercruiser 5.0 mpi, Bravo III
    Most likely the IAC sensor (Idle Air Control) as others mentioned
     
  17. techmitch

    techmitch Well-Known Member GOLD Sponsor

    May 1, 2008
    Chesapeake Bay, Middle River/Frog Mortar Creek MD.
    1999 270 DA
    Twin 4.3s W/Alpa I Gen II's
    What the hell kind of protocol is that. How about doing some testing instead of wasting time throwing parts at it.
     
  18. techmitch

    techmitch Well-Known Member GOLD Sponsor

    May 1, 2008
    Chesapeake Bay, Middle River/Frog Mortar Creek MD.
    1999 270 DA
    Twin 4.3s W/Alpa I Gen II's
    The IAC is not a sensor. It is a PWM output controlled solenoid/actuator. Sensors are inputs.
     
  19. Wanderer 290

    Wanderer 290 Active Member

    162
    Jul 1, 2019
    01 sea ray 290 sundancer
    Twin 5.7 b3’s
    Previously mentioned testing provided no resolution.
    Actually swapping parts is is a common practice in auto dealers in that a mechanic pulls parts from the shelf, installs them and if the problem is not resolved will return the part to the shelf and reinstall the original.
    The swapping of parts between engines and other systems is also common in the aircraft business too. For the purpose of trouble shooting...
     
    Last edited: Mar 5, 2020
  20. 370Dancer

    370Dancer Well-Known Member

    Oct 2, 2006
    Florida - Alabama
    1998 370 Sundancer
    380hp MAG MPI Gen VI with V drives
    Yes, the Idle Air Controller is not a sensor. It's a controller. Here's what it does. When you have the throttles completely down, your butterflies on the intake should be completely closed. that means no air to speak of should be mixing with the fuel to create combustion except what is allowed. The idle air controller is controlled by your ECM. The ECM is looking at idle speed, and other stuff to determine whether or not your engine needs more air to keep running. If it does, then a little stepper motor moves a plunger back and forth to help maintain the correct air/fuel mixture to keep your engine running.
    If you have to open your throttle to start and keep your engine running, then your IAC is probably not doing its job. When you move your throttle, you are allowing the butterflies on the intake to open, bringing more air into the mix. Your ECM senses this, and allows more fuel to keep the ratio correct.
    I don't know about the 6.2 specifically, but if I have to change an IAC, that involves removing the intake plenum, flipping it up, or over, and replacing it, and the intake manifold gaskets on the way back to locking it all down.
     

Share This Page

Show Sidebar