90HP Optimax Struggling to idle, dies @ WOT, can't fish past dock

[paco]

I have a 90HP 2009 Optimax that struggles to idle (see video: ). Didn't write down the SN before I had left the storage facility and it's a few hours away.

The boat was running fine one day, but then we started getting the 4 beeps water in fuel. Went back to the dock and drained out the VST. Boat sat for about a month and when we went back to run it, it was acting like this. We found out the middle cylinder wasn't firing, and after troubleshooting it got the cylinder to fire up by replacing the air injector. Went out boating and she ran fine for about 5 minutes, and then when running WOT it would just shut off and die. Putted back to the dock - and now the motor is exhibiting the symptoms in the video.

I have replaced the spark plugs, sent the air injectors off and had them cleaned & tested (all good), replaced the fuel injectors, and taken apart the VST and cleaned it. Swapped out the three coils with three other coils from another optimax. Same problems.

Maybe related/unrelated: There is a fuse box with three fuses in it under the cowling. One of them is a 15amp fuse that had blown (twice) when we first had problems. Replaced it, and it doesn't blow anymore - but - if we completely remove the fuse and crank the motor it fires up just the same, with or without it. The fuse doesn't go to the trim. I would suspect that whatever this powers is the culprit if it's something fuel related.

Any ideas guys?

[EuropeanAM]

Need to check the BASICS:

-Compression
-Spark
-Fuel Quality, Delivery and ** Air/Fuel Pressures **

[paco]

Fuel pressure is terrible. After going through everything and replacing the pumps, I've narrowed the problem down to something in the rail (I think). When I turn the key once to kick the VST pumps into gear, fuel immediately comes out of the line that returns fuel to the VST. To figure this out, I disconnected the nozzle at the bottom of the VST and placed my finger over the hole to make sure it maintained pressure, which it did. When I turned the key once fuel came right out of the hose that was still connected to the VST. The rails only maintain pressure around 30 psi. When I try to crank the motor I also notice an air mist coming out of the ported holes on the air pressure diaphragm. I checked the fuel diaphragm and there were very subtle shredding along the edge of it - but no large tears. Thoughts?

[EuropeanAM]

Stop there. You have problems in the rail that need to be addressed before proceeding. Regulators can be repaired- but the regulator calibration must be verified after repair (and reset as necessary).

NOT a "DIY" task. Do not attempt to open the air regulator as the spring is strong enough to leave a pretty big mark (or worse).

[leonreno]

Did you check your gas tank for water, you said it was giving off a water in fuel alarm and you cleaned the VST but did you check or drain the tank?

[paco]

Sorry for the delayed reply here guys - just now got around to looking into it again. We had drained the fuel out completely, so can't be water anymore. I did buy another fuel rail and connected it today, but have the same problem. When we crank the motor the fuel pressure is horrible, and only the first two cylinders ignite. When she's sputtering, we test the schrader valve on the rail and there's only a slight trickle.

On the first key turn, we're at 40psi fuel when the high pressure pump activates without the motor on when the gauge is connected. If we turn the key once to activate the high pressure pump without the gauge connected and test the pressure after 30 seconds of waiting, there is no pressure. When the motor is fired up, there is fuel leaving the fuel rail and sent back to the VST through that one tube above the 2nd fuel injector (which makes sense because the 2nd and 3rd cylinders are having problems firing with no fuel).

Could there be something other than the fuel diaphragm causing the fuel rail to send fuel back to the VST and killing the pressure, or is that the only trigger? We did buy the rail we just connected online, "slightly" used they said. After installing it and realizing we had the same issue we opened up the fuel diaphragm and it was perfect, aqua in color and no tears. Put it back on, and same problem.

[EuropeanAM]

Really suggest you get to the BASICS in Post#2. Properly testing pressures requires a DUAL PRESSURE liquid, or glycerin dampened gauge set.

You must test AIR and FUEL pressures at the SAME TIME.

Fuel pressure is equal to AIR PRESSURE + 15 psi. Test pressures and record results for:

-At idle
-Under Acceleration
-5/10/15 seconds after engine shutdown (restart for each test- must be intentionally SHUT DOWN- not a "stall").