2006 Mercury 25 EFI 4-stroke dies after 10-15 minutes at WOT

[Ozellotrail]

Dies after 10-15 minutes WOT after first putting boat in water. Motor will immediately re-start, but idles rough and dies again. If it cools for 10 minutes or so, it will re-start and get back on plane, but then dies again. After 1st incident, I found my fuel hose lining had deteriorated, and the filter/separator bowl was full of debris. I replaced the fuel hose and cleaned the lines from the quick connect all the way to the lift pump. Next trip, motor idled about 100 yds. from the ramp and died. Would start again, but died immediately. Pulled lift pump, found junk in check valve, cleaned and re-assembled. Next trip, back to original problem, died after 10-15 minutes at WOT. Pulled cover, noticed filt/sep bowl was empty. Pumping bulb filled the bowl, but didn't seem to help engine run any better. The only thing that seems to help is time to cool off, but then it will only run for a minute or so, then die again. I have a good water stream coming out of pee hole, and this is downstream from the fuel cooler, so I wouldn't think this is vapor lock, but it sure seems like it. Thanks in advamce for your help!

 

[ondarvr]

Electrical components tend to fail in that way, but it could still be a fuel issue. Check for spark when it dies.

 

[Ozellotrail]

Seems odd that the filter/separator bowl goes empty. I did a suction test on the fuel line and tank, and checked the vent cap, and everything seems fine. I would think that if there were no air leaks on the fuel system upstream of the bowl, that it would remain full, unless pressure in the system was driving the fuel back into the tank. Hope that made sense...

 

[ondarvr]

Can you plug it in and read the codes?

 

[Ozellotrail]

I don't have any diagnostic software or code reader, and was trying to avoid getting a dealer involved. The engine doesn't beep or flash engine light when this occurs.

 

[ajgraz]

You mentioned filter separator bowl, is that under the cowling? Is that before or after the pump? (I would think before)

Is there another filter after the pump but before the rail/injectors? (Maybe a pleated paper filter or a plastic inline cylinder, anything?)

You may still have a fuel blockage somewhere from the debris, I hope in another filter down the line (rather than in rail/injectors)

 

[Ozellotrail]

The bowl is under the cowling, between the fuel quick connect, and the lift pump. There is a sealed high pressure filter between the high pressure pump and the injector rail. That is a possibility, but seems odd that it runs normally until it gets to running temperature. I just finished disassembling and inspecting the vapor canister where the high pressure pump lives. There is a strainer on this pump (clean), and a float and needle valve assembly like in a carburator. I took this apart, and there might have been an obstruction in the needle valve. I'm presently changing the lower unit lube, as I found another post where someone's lower unit was binding up when it got hot. Unlikely, but I'm grasping at this point. The old gear lube looks great (whew). Going to finish up, and run it on the muffs for a while...

 

[AnthonySci]

One possible explanation---a piece of old fuel line remains lodged inside the fuel path in an area that is in close contact with the engine block; when "cold" it's only a partial obstruction, when the motor warms up, with heat comes expansion---and then the fuel delivery is severely restricted?

 

[Ozellotrail]

AnthonySci, you were very close. When the fuel hose liner disintegrated, some of the debris got past the filter/separator element. I had found that this material had wedged open the lift pump check valve. But it was also blocking the seat of the float/needle valve which controls the level in the vapor cannister where the high pressure pump lives. This allowed me to run WOT until cannister was empty, stopping the engine. Residual lift pump pressure and pressure from the priming bulb would push a small amount of fuel past the blockage, allowing it to start again, but it would only run a few seconds. The longer I waited, the more time for the fuel to get past the blockage. I got the blockage out using liberal applications of carb cleaner, and compressed air, as there is no way to disassemble this valve seat. I made a cheesecloth catch basin, so I could see if I was flushing out any debris. I replaced the factory filter/sep element, and added a small in-line filter between the lift pump discharge, and the vapor cannister inlet. Just got back from running WOT for 35 minutes. Success!