Problem Start Condition

I have a 1999 29 foot Powerquest Enticer FX with twin 454 MPI Mercruisers. Both motors fire up instantly when we put the boat in the water right off our trailer. We then go thru an extended no wake zone before running at about 3,500 RPM. Both motors run well. We then go to our favorite anchoring spot in Tampa Bay called Bear Can Island. After about 4 hours we decide to start packing it up. Once we start either engine both will fire up for only about one second and then stall. We now need a tow back to the dock. This has happened three to four times. Sometimes one engine will finally stay running and while limping back to the dock the other engine would finally start with just the click of the key. I have purchased a Mercruiser scanner and both engines have not thrown any codes which just makes it more interesting. I really want to get to the bottom of this situation because it is taking the fun out of going out for the day worrying all day long if we will be able to make it back to the dock. You would think it is a fuel system problem. Both water separators have been replaced to no change. There are two fuel lines coming out of the gas tank going to each separate fuel pumps on each motor. This problem has not occurred while the boat is on the trailer. It only happens when the motors have run and shut off for about 3 hours. For all apparent reasons you would think both motors are not getting fuel on start up. Once they do get running they both perform well.

you need more investigateing if your good at checking engines we can get to the bottom of this. get a spark testor when eng dont start see if we have spark? IF YES a can of choke cleaner spray some in air horn. if it almost starts your not getting fuel.now you need a fuel presssure gauge thers a shareder valve some where the fuel rail.you need to look up spec for your motor. if pressure is off or none could be bad pump or electrical prob.you need to look at a wireing dia.some fuel pumps run a signal through the oil pressure switch.you can run pump with a jumper wire.if it runs and pressure is good ck electrical system. if it runs but still not good pressure line or tank prob.try and aux tank back to the top if spark is good and pressure is good.fuel injectors could be bleeding down when hot causing eng flooding. see if you can pull the center spark plugs see if there wet with gas. have you tried starting with throttel wide open if it starts then thats what you have too ck. you will have to do your home work frist for specs this may seem like a lot thats what i would do good luck

Thanks for your information. Over the weekend I hope to find some time, besides having to do yard work, to find the cause. Would flooding still allow the motor to start for a second or two before stalling because that is what is happening? If I keep attempting to start it, after about ten attempts each motor will finally fire up and run as if there never was a problem. Very frustrating issue I need to fix.
Thanks

you need to spray some choke cleaner in air box if it starts right away rent a gauge ck fuel pres when yu turn on ing and while cranking. and when it starts good pres it got t be injector circuit prob

bcclew said:

you need to spray some choke cleaner in air box if it starts right away rent a gauge ck fuel pres when yu turn on ing and while cranking. and when it starts good pres it got t be injector circuit prob

Click to expand...

I did purchase a fuel guage from Advance Auto. I will try hooking it up over the weekend. Just so you know this problem only happens after the running for about one hour, getting to our local hangout and then trying to start after the motors sit off for about 3 to 4 hours. That is why I suspect it could be some of the injectors are leaking fuel causing a flooding condition.