50hp 4 stroke fuel starve

[Limit_Out]

I'm stumped. I've got a 2003 efi merc 4 stroke. It used to run perfect at full throttle at 6000 rmp. Recently, while fishing in mid december in cold conditions, it began to surge in and out of power at 5000 rpm. I changed the fuel, checked the filter, replaced plugs, oil change, and replaced the fuel line assembly from tank to motor. Is there something else I can do without taking it to the dealer? Maybe fuel pump or a pressure guage? It also starts and runs perfect until it hit 5000 rpm. Even jumps out of the hole full throttle great till the dreaded 5000. Thanks in advance. Mike

 

[hkeiner]

Re: 50hp 4 stroke fuel starve

Mercury issued a Service Advisory that provides some fuel starvation troubleshooting guidance. It applies best to carbed motors, but it may still be of some help troubleshooting starvation symptoms on your efi motor. The below link discusses fuel starvation symptoms in more detail and also contains a link to the Service Advisory.

Others may have additional and better advice specific to the efi motors.

Good luck


http://forums.iboats.com/showthread.php?t=224246&highlight=fuel

 

[Limit_Out]

Re: 50hp 4 stroke fuel starve

Hey thanks alot hkeiner. I appreciate it.

 

[Limit_Out]

Re: 50hp 4 stroke fuel starve

I've been told that a spring could be bad, something about a pressure switch. But the person who told me was not sure exactly about the spring, just that he had it replaced on a similar motor. Does this ring a bell with anyone? Thanks much.

 

[rodbolt]

Re: 50hp 4 stroke fuel starve

two things ya gotta do.
one is a fuel system vacum check, T a vacum guage at the ful pump inlet at WOT the system vacum should be 1-4" Hg, if less than 1 look for an air leak if more then 4 look for a restriction. restrictions can be fould by moving the tee back to the next connection poit on the fuel line.
2nd is the fuel rail pressure should be able to maintain about 35 PSI at wot, if it cannot inspect the high pressure pump filter for debris. also remember each injector has a screen as well.
thats why most brands reccomend a 10 micron water seperator in the system.

 

[Limit_Out]

Re: 50hp 4 stroke fuel starve

Thanks alot Rob. Looks like I will have plenty to do this weekend. I appreciate the advice.

 

[Don S]

Re: 50hp 4 stroke fuel starve

Here is a link to a Merc service bulletin that explains a little more about what rodbolt was referring to.

http://www.marinepartsman.com/Mercury-Marine-service-bulletins/Mercury-Mariner/2001/EN_17.PDF

 

[CharlieB]

Re: 50hp 4 stroke fuel starve

You stated that you 'checked the filter'

fuel filters do NOT give warnings that their maxumim flow is reducing, I highly recommend that you go ahead and change the filter and retest.

Remember, a reduced WOT RPM and surging is generally caused by a fuel restriction/supply, aka., going LEAN!!!! Which can and will destroy your engine.

Besides checking the main fuel pump vacuum, also check main pump pressure.