2000 Merc 150EFI Runs great except at idle

My 2000 Merc 150EFI runs great on a hose pipe at the house. When running at the river, it runs great at first at idle/WOT, then after an hour or so the motor will die at idle. I can probably run all day at speed. The motor will not start back, it acts as it is starving for fuel. It will turn over and sounds like it chokes down.

This has been going on for a while, i have changed everything related to fuel. I changed fuel suction line in tank, all fuel lines, filters and fuel pump. I brought it to shop and he changed everything i changed. New hot plugs also.

I am pretty sure it is not fuel related and looking for electrical issues, but not sure what to look. stator maybe?

Any Suggestions?

Re: 2000 Merc 150EFI Runs great except at idle

anyone?

Re: 2000 Merc 150EFI Runs great except at idle

This very well could be the stator. If yours is like mine, there are four coils on the stator, two for low RPMS and two for hi RPMs. If you have a low side cutting out when it gets hot, it would produce what you are experiencing. You could do a couple of things. Run the boat until it happens and see if you are loosing spark (or week spark) on three cyl after it heats up. You could also check the ohms on the stator to see if it is to spec. The bottom line is you have to figure out what spark is disappearing on you when it heats up. If it happens to three cyls (1,3,5 or 2,4,6), look at the stator, two cyl, (1&2, 3&4, or 5&6), look at the trigger, one cyl, look at the coils. I use an iductive timing light for a quick way to check on the water

Re: 2000 Merc 150EFI Runs great except at idle

Thanks for the info. I will be replacing the stator and trigger soon. Eliminate those from being the issue.

Re: 2000 Merc 150EFI Runs great except at idle

OK, i changed stator and trigger and that was not the issue here, it is not electrical but indeed fuel related. I have noticed that when the motor dies, there is a high amount of air in the fuel line. Most times i need to open up the fuel line by the fuel pump to purge the air out of the line with the primer bulb. There is so much air in the line that no matter how much i pump on it the motor will not start. It is like the motor is forcing air back in the fuel line. Would could cause this?

Again, i have replaced every thing fuel related outside the motor, so the issue must be inside the motor. Maybe a reed valve? i give up.

Re: 2000 Merc 150EFI Runs great except at idle

If you are getting air before pump you have a supply line sucking air thru a crack or loose clamp or bad/cracked pickup in tank, water seperator filter loose.

Re: 2000 Merc 150EFI Runs great except at idle

I'd be looking at that primer bulb. Get a quicksilver if you don't have one already. I've had problems with Moeller and other brands sucking air. The other thing to check is your fuel/water separator. They're making them now with longer throats on the head because the older ones would aereate the fuel. You should be running one with at least a 1" hole.

Re: 2000 Merc 150EFI Runs great except at idle

Ya might wanna get tha tpi checked. They can do some strange things (at idle) when actin' up...............

Re: 2000 Merc 150EFI Runs great except at idle

I have changed all suction lines and primer bulbs 3 times. Also the water separater. I do have quicksilver primer bulbs also. I have twins and even swapped the fuel lines on the motors. Still same motor acting up. So it has to be internal.

Re: 2000 Merc 150EFI Runs great except at idle

This is a very simple system and is air at mechanical or high pressure pump? If at high pressure pump you have a problem in the VST tank.. Here is simple fuel flow for that engine:
fuel leaves tank thru pickup in tank,primer bulb draws it from tank and pushes it to mechanical pump which then fills water separator and sent to VST tank, float in VST opens/closes to keep VST from overfilling, high pressure pump pushs fuel thru upper filter to fuel rail, fuel rail supply is controled by pressure regulator which returns excess to VST.