Merc 496 fuel pump issue

Discussion in 'General Maintenance/Repair Questions' started by Ryanm51981, Jul 14, 2020.

  1. Ryanm51981

    Ryanm51981 Member

    77
    Apr 10, 2012
    Peconic Bay NY
    2006 Sea Ray 290 ---- SOLD
    2006 380 Sundancer - current
    8.1 Mercs v drives
    Hey guys ,
    I took my boat out for a ride today when suddenly the port engine died and couldn’t be restarted . I cracked open my cool fuel module to check the filter and noticed it was pretty much empty . That lead me to believe my fuel pump wasn’t working . I ran to my local marine supply store and he only had the high pressure fuel pump in stock ( a Hail Mary attempt we were supposed to go on a trip tomorrow ) so threw it on but no dice . I noticed when I cycle the engine on I don’t have the high pitched wine anymore like my starboard motor does . I only hear a low hum of one of the fuel pumps . My mechanic is likely two weeks out . Its def fuel related , not the IAC sensor .

    Bad relay somewhere ? Bad fuse ?
    anything else I can try ?
    Merc 496 8.1 2006

    please help !
     
  2. paulswagelock

    paulswagelock Well-Known Member

    Oct 25, 2010
    pa
    2018 SDX 270 OB 300 Verado
    Verado 300
    Unplug it and put a voltmeter on the plug. Should see 12v for 5 seconds when key is turned on. If yes, bad pump. If no, go check the fuel pump relay. You can swap them between motors to see if the problem follows.
     
  3. Ryanm51981

    Ryanm51981 Member

    77
    Apr 10, 2012
    Peconic Bay NY
    2006 Sea Ray 290 ---- SOLD
    2006 380 Sundancer - current
    8.1 Mercs v drives
    Thanks a lot , any idea which one is the fuel pump relay ? Having a little difficulty locating it .
     
  4. paulswagelock

    paulswagelock Well-Known Member

    Oct 25, 2010
    pa
    2018 SDX 270 OB 300 Verado
    Verado 300
    Try chasing down the wire colors from this diagram to see if you can locate the relay.

    126A143A-4195-47E9-B138-2E4BEAA59DC5.png
     
  5. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    If it's making some noise it must be getting voltage. Probably the other pump.
     
  6. Ryanm51981

    Ryanm51981 Member

    77
    Apr 10, 2012
    Peconic Bay NY
    2006 Sea Ray 290 ---- SOLD
    2006 380 Sundancer - current
    8.1 Mercs v drives
    I tried switching all the relays around since they are all the same but that didn't help . My mechanic came down and put a gauge on the shrader valve after bleeding out some air and we got the boat started but after a few minutes the boat stalled and couldn't be restarted. Im not getting any fuel to the filter before the pump.We blew back air into the tank and heard bubbles with no resistance, we pulled fuel from the tank with no resistance. We took both pumps out and tested them and they both work. They both prime and pump fuel . I don't get it and my mechanic cant figure it out either. The only thing I think is weird is I don't hear that high pitched whine when I cycle the key on like I do with my starboard motor but again the lift pump appears to be functioning after properly. What are we missing ???Please help I had a big trip planned, family coming out with hotel rooms booked and we are stuck at the dock. Is there any chance the lift pump is just working intermitantly?? .
     
  7. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Sounds like it. If it's not making noise it's not working.
     
  8. Ryanm51981

    Ryanm51981 Member

    77
    Apr 10, 2012
    Peconic Bay NY
    2006 Sea Ray 290 ---- SOLD
    2006 380 Sundancer - current
    8.1 Mercs v drives
    its just strange when its pulled out of the cool fuel box and bench tested it work as soon as you apply voltage to it. When you cycle the key you only hear a low hum of the other pump
     
  9. Ryanm51981

    Ryanm51981 Member

    77
    Apr 10, 2012
    Peconic Bay NY
    2006 Sea Ray 290 ---- SOLD
    2006 380 Sundancer - current
    8.1 Mercs v drives
    I’m already 350 bucks into it for a pump I didn’t need ..... I’m not sure if I should purchase the lift pump now
     
  10. Espos4

    Espos4 Well-Known Member

    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    Check for power AND ground at the wire harness. Could be a bad connection or corroded wire.
     
  11. Ryanm51981

    Ryanm51981 Member

    77
    Apr 10, 2012
    Peconic Bay NY
    2006 Sea Ray 290 ---- SOLD
    2006 380 Sundancer - current
    8.1 Mercs v drives
    Ok I will . I just realized that my mechanic was working on the boat with the fuel canister empty . I was reading that fuel canister had to be full to prime the pump and start pulling fuel from the tank .
     
  12. Espos4

    Espos4 Well-Known Member

    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    Primed or not, the pump should run when the key is first turned to “run” and you stated that you don’t hear that.
     
  13. paulswagelock

    paulswagelock Well-Known Member

    Oct 25, 2010
    pa
    2018 SDX 270 OB 300 Verado
    Verado 300
    When my cool fuel module died, it was intermittent. It would stop pumping and the motor would stall. Let it sit for 30 minutes or sometimes an hour, and it worked perfect again, as soon as it got hot, it will just stop again. You might have the same issue.
     

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