Mercruiser 4.3 MPI/Bravo 3 . Th engine dies at high RPM. Possible vacuum leak?

[diver94]

Hi,
I have a 2003 Regal Comodore 2860 with dual mercuirsers 4.3MPI. I was running the boat yesterday; everything was going well (both engines were reaching 3,800 RPM). Suddenly, I heard two beeps and the port engine died. The starboard engine was fine. I was able to re-start the port engine and just keep it under 2500 RPM in order to come back to my dock. Both engines had good oil pressures, 175 degrees temp and the outdrive oil reservoir were in operating range (i re-filled the reservoirs two days ago).

Note:
I was working under the port engine two days ago (trying to reach a screw driver that fell under it). The space is very tight there and I had to go all the way under it. When I started to come back out from under the port engine, I felt like my shorts got caught in something and I heard a soft pop/ like a short air pressure hissing noise (similar to what you hear when you remove the valve form a car tire). I was unable to find the lose hose or fitting.

Is it possible that a fuel vacuum line (or anything related to fuel pressure) is lose and restricts fuel or air at high RPM? If so, where is the best part to find it?

Thanks
Lui

 

[jrs_diesel]

Vacuum leaks usually cause engines to run bad at idle, when the vacuum is the highest in the intake manifold. Running at speed, the vacuum will be much lower, almost close to atmospheric pressure when the throttle is wide open. I don't suspect a vacuum leak in your case, nothing on your engine uses vacuum.

Which side of the engine where you? If closer to the port side, you may have bumped one of the fuel lines, those are all on the port side.

Did you see any water in the bilge after this? I'm wondering if you may have knocked a water hose loose. Is your engine raw water cooled, or do you have closed cooling?

In either case, the "hiss" was likely air entering a hose with the water or fuel (don't know which) draining back to the fuel tank or the outdrive. Look over all of your hoses and connections carefully on your port engine and see if anything looks amiss.

 

[diver94]

Vacuum leaks usually cause engines to run bad at idle, when the vacuum is the highest in the intake manifold. Running at speed, the vacuum will be much lower, almost close to atmospheric pressure when the throttle is wide open. I don't suspect a vacuum leak in your case, nothing on your engine uses vacuum.

Which side of the engine where you? If closer to the port side, you may have bumped one of the fuel lines, those are all on the port side.

Did you see any water in the bilge after this? I'm wondering if you may have knocked a water hose loose. Is your engine raw water cooled, or do you have closed cooling?

In either case, the "hiss" was likely air entering a hose with the water or fuel (don't know which) draining back to the fuel tank or the outdrive. Look over all of your hoses and connections carefully on your port engine and see if anything looks amiss.

No water in the bilge after that ( at least I didn't notice t)t. I have a raw water cooling system (new impeller and water pump installed in May). My head was closer to port side, but the part of my body that got tangled was towards the starboard side (of the port engine). I think the fuel filter (water fuel separator is on the starboard side of the engine..when you look at it form the front).
Ok. I will go back to the boat this afternoon and will slowly all the hoses/fittings.

THANKS!!

 

[alldodge]

Suddenly, I heard two beeps and the port engine died

Sounds like you lost main power to the motor. This is either a bad connection or relay dropped out. There are two relays on top the motor, one main power and the other is fuel pump, they are both the same and can be swapped. Check battery cables at both ends and don't over look the grounds

 

[diver94]

Sounds like you lost main power to the motor. This is either a bad connection or relay dropped out. There are two relays on top the motor, one main power and the other is fuel pump, they are both the same and can be swapped. Check battery cables at both ends and don't over look the grounds

AllDodge,

I think you are right. When I turn the port engine key...sometimes I hear the alarm beep, and sometimes it wont (no beep noise). However, the engine starts Ok. But I still dont understand why the alarm does not beep on the port engine all the time. There were a cpl of times last year when the port engine wouldnt start and I had to wait (I couldnt figure it out), but it has been working Ok since.

I will start looking into the electrical.
Thanks!