I assume your 30 PSI fuel pump pressure was taken while idling and sitting at the dock, correct? Flow requirements are minimal at idle compared to 4500 RPM. Its possible you are not getting the flow (volume) needed at 3000 RPM and higher which seems to you as if in ‘safe mode’. Your lean (whitish) plugs seem to indicate lack of fuel. And easy to restart since not needing that much flow.
Restricted flow could be from a bad or contaminated fuel pump. And here are some other causes:
- Clogged (not completely) fuel filter; note a slightly loose one will cause the pump to suck air and thus run out of fuel, so make sure its tight.
- Your fuel pickup (in the tank) may have a screen on the bottom of it that is clogging up. A lot of older pickups have this screen.
- There is an anti-siphon valve at the top of the tank prior to hooking onto the fuel hose. This one-way check valve prevents the fuel line from draining back into the tank (if it did you would have a hard time starting each time and eventually burn out the pump). These siphon valves can also get ‘sticky’ and block flow intermittently, starving the fuel pump.
- The fuel line itself can deteriorate over time and the inside lining starts to degrade to the point where it collapses (internally) causing a blockage (with no external signs of an issue).
- And there may be a kink or pinch in the fuel line that is not obvious.
- And the tank could not be venting.
But the most suspect ones are fuel pump and anti-siphon valve.
Suggest you do this: with a 2nd person on the boat, hook back up the fuel pressure gauge. Place it somehow so it can be monitored and not get in the way of spinning parts. Go for a ride. If get up to about 3000 RPM and the pressure starts to drop, well now we know where to start looking.
Try this test and post results and we’ll go from there…
. And other potential issues addressed. So now it’s into the computer as you suspect. Only thing I can think of is to use a test light hooked into the backside of the injector plug and seeing that the signal to fire the injectors ‘goes away’ or diminishes when hit that 3000 threshold would defiantly point back to the ECM. I have never done this so unsure if there is sensitivity to the resistance of the light or needing to be a led or some such to preclude harm to the ECM. Best to get the appropriate ECM diagnostic tool. Other than that, I cannot help further, sorry.
