1997 merc 225 efi loss of power when warm

[njcowboy]

Hoping someone can come up with a miracle.
Long one short, Good spark, good compression, good fuel pressure.
Boat starts up and idles great. Hole shot is great, can run at 5800RPM but after about 25 minutes, power drops out.

Won't go over 2500 RPM. No errors on the system gauges

coils and stator test good

Could a diaphragm fuel pump cause this? but only when it heats up? Tech is leaning towards that but I think he is scratching his head at this point

One side note, the system gauge is brand new, light bulbs are good on it, but when the engine is started, only one of the lights comes on and the horn beeps as normal to let you know the system gauge is working.

​Any thoughts?

 

[alldodge]

I would install a fuel pressure gauge on the high side and see if it starts falling off

 

[Glastron_V210]

Have you checked the fuel tank vent? What happens if it is blocked is that the fuel pump draws a vacuum in the tank until it can't pull any more fuel.

One way to tell is to run it until it starts running poorly, then open the fuel tank fill. If you hear a sucking sound, the tank vent is clogged.

Or just check it out really well.

Chay

 

[njcowboy]

Fuel pressure gauge shows 38 psi with a variation at WOT of 1-2 PSI
Same pressure when it dies as when it is running great
There are two seperate ECU's on the back of the motor, Can anyone tell me what the top and bottom one does?

 

[alldodge]

Fuel pressure at 38 +/- psi from idle to WOT is where it should be. So even when its loosing power the fuel pressure is steady?

Don't know about the modules but my guess would be they are in this manual somewhere
http://boatinfo.no/lib/mercury/manuals/105and140jet-135-150-175-200-225.html#/0