2004 Johnson 4-stroke fuel injected surging problem

[venuspie]

I have a 2004 Johnson 90hp 4-stroke fuel injected engine on a 22 ft. pontoon. It has sat for 3 years straight and I have been going though it. All new maintenance parts installed and had to clean out the fuel tank as well. Took it on the lake today and ran it. Takes off like a rocket and runs at 5k rpm for about 30-45 seconds. Then starts surging and rpm's start falling. Bring it back to idle and then hit it again and same thing. Runs great for a min then slowly dies. Over and over. Any ideas?? I have replaced everything beforehand and I am leaning towards a bad or clogged fuel vapor separator. Not wanting to take the intake off but I am out of options. Maybe a sensor? Any help is greatly appreciated. Thanks

 

[daselbee]

Most likely a bad HP fuel pump. To debug it properly, you MUST get a fuel pressure gauge on the fuel rail to monitor fuel pressure at speed.
The fuel pressure must maintain 40 psi.
I use a spare banjo fitting like the one at the bottom of the fuel rail, and installed it in the plug at the top of the fuel rail, and then attached the pressure gauge there.

There is also a fuel pressure regulator buried in there somewhere. Over the years it has been moved to different places on the output of the HP fuel circuit.
It is probably inside the vapor separator at the bottom. That is a device that will control the overall fuel pressure too.

There is a small filter under the HP fuel pump. Don't forget to check that.

These four strokes will NOT do well sitting for 3 months, not to mention three years.....
I had a DF-70 HP fuel pump lock up after just three months of not running.

 

[daselbee]

Re-reading...I see that it runs great for a minute then dies.....It could be that the fuel lift pump is not supplying enough fuel to the input of the vapor separator and the vapor separator is running out of gas.
To test that, pump your primer bulb continuously, providing a manual assist to the lift pump. See if it keep running then.

There are no sensors for any of this fuel supply circuits.

 

[venuspie]

Thank you for responding. I fear the whole separator needs replacing. I am finding prices anywhere between $600-$700 just for parts. I'll do all The labor myself. I will get pressure gauge set up asap and will try primer bulb trick. I removed the lift pump and manually worked it and it seemed fine. I forgot to mention that I believe i am also getting fuel into the oil as well. Oil level keeps increasing but it is not water intrusion.

 

[sea-note]

Venuspie,

Did you ever get to the root of the issue?

 

[GA_Boater]

Venuspie,

Did you ever get to the root of the issue?

He never came back.

Closed.