Having a fuel pressure issue on my port side engine. At idle it is way above spec, 40-45 psi when it should be 30 or less like the other side. At 3000 rmp it will run stable at 30 psi (electronic gauge) however any more and the pressure drops to 15 or less and the knock sensor starts killing the engine....scary stuff.

My question is what should I chase first? I have cleaned the entire fuel system. Engine has 4 hours on it (boat sat unsold) filters are clean. I even took apart the injectors and cleaned them.

We have a mechanical fuel pump, to an electronic boost pump in the fuel cool, and a regulator down there as well.

Any help would be great. Sending unit for pressure guauge is mounted at the "T" for the fuel lines before the TBI's

Thanks

I'm no expert, but I recently dealt with some fuel pressure gremlins on my starboard 575 as well. My symptoms were a little different and not quite to the point of the engine going into power reduction mode.

With it running high fuel pressure at idle, I would start looking at your vacuum line first. While it's idling, pull the vacuum line off the throttle body and see if the pressure jumps up. If not, you can start to narrow your focus to a possible issue with vacuum or the regulator on the fuel cooler. I'd also get a mechanical gauge on the schrader valve on the throttle body to get a more accurate reading. Check the pressure when you turn the key to the on position prior to firing it up. If it reads 28-30lbs and then jumps up over 40lbs when you fire the motor, again, it sounds like vacuum or the regulator are a good place to start investigating.

The other thing worth checking for is a bad MAP sensor. You can swap the one from the other motor real quick to eliminate that as a possible issue. All of this is assuming the fuel injection system is all stock and hasn't been modified.

Hope that helps man. Let us know how the trouble shooting goes.

You have the advantage of a second good motor to swap parts from to narrow down the issue.

Before swapping regulators, I would definitely call Mercury Racing. You have some good symptom information to share. They know the theory of operation for your fuel system and can offer the most probable cure.

I had a high fuel pressure issue on my 600sci's, and the advice given by the tech department solved the issue even though it did not seem possible. The advice was based on experience and it was accurate.

Thanks Kelly

Yes, looking at the fuel system on the parts explosion.....it doesn't make sense I will give them a shout

Kelly,

Just got off the phone with Merc support. He told me there are two screens on the pump it self in the cooler, and one screen on the regulator. Because of the age of the boat not being ran, and the crap that was in the fuel system before I cleaned it he wants me to check there first.

I'll give it a shot, thanks for the info....I didn't even expect them to answer the phone

Cleaned the screens, it got better, but was still not right. Idle pressure was at 60 psi! Pump stopped dead, took it apart and it starting working again. Tried it again and all pressure was reading normal? 30 psi at idle and 28 psi on boost at high rpm. Ran to 4500 rpms @ 80 mph, punched it and it stayed with me.....ran like a new boat. Ordering a new pump and regulator tomorrow overnight, I don't trust this one. Still confused.

The are fun to get at being under the motor. FYI...the standard regulator can be upgraded to an adjustable one from CP. Just not real fun to install/adjust.

I hear ya, the first time was a pain but now I have it down where I can get in and out in 15 mins. I have lots of room in front and under the engine.

Was thinking about changing the whole system out to something simple from Aeromotive.....how important in the fuel cooler?

I hear you on that