Merc 496 fuel pump issue

Ryanm51981

Member
Apr 10, 2012
78
Boat Info
2006 Sea Ray 290 ----
2006 Sea Ray 38 Sundancer
Current -Ocean Yachts - 48SS
Engines
Mercury
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 !
 
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.
 
Thanks a lot , any idea which one is the fuel pump relay ? Having a little difficulty locating it .
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.
 
Try chasing down the wire colors from this diagram to see if you can locate the relay.

126A143A-4195-47E9-B138-2E4BEAA59DC5.png
 
If it's making some noise it must be getting voltage. Probably the other pump.
 
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?? .
 
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
 
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
 
Check for power AND ground at the wire harness. Could be a bad connection or corroded wire.
 
Check for power AND ground at the wire harness. Could be a bad connection or corroded wire.
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 .
 
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 .
Primed or not, the pump should run when the key is first turned to “run” and you stated that you don’t hear that.
 
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.
 
Hi @paulswagelock

I think I have the same problem.
My boat starts no prob. It runs well at high speed. When going a low rpm for 20 min it stalls and will not start. After 45 min or so it starts perfect.

The water tubes going into the Cool fuel module are dirty.

would you recommend changes the Cool fuel module or is there a cheaper fix?

my mechanic recommend change the main water cooling hose. But the is require to get the boat out of the water.
 
Hi @paulswagelock

I think I have the same problem.
My boat starts no prob. It runs well at high speed. When going a low rpm for 20 min it stalls and will not start. After 45 min or so it starts perfect.

The water tubes going into the Cool fuel module are dirty.

would you recommend changes the Cool fuel module or is there a cheaper fix?

my mechanic recommend change the main water cooling hose. But the is require to get the boat out of the water.
Might be best to start your own thread for this. This thread is to try and solve this specific issue. Others issues dilute the original intent.
 
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 .
I am sure you are feeling the pressure right now of trying to get your trip underway, family coming etc. But consider yourself lucky this didn't happen out on the water, far from home, supplies, etc. I would follow the advice here and slow down. Start your diagnoses with the electrical tests with everything in place. Just be systematic, and use process of elimination. Don't just keep throwing parts at it. Have family go find other activities until this is resolved. Please keep us posted.
 

Forum statistics

Threads
112,950
Messages
1,422,871
Members
60,932
Latest member
juliediane
Back
Top