Explain This to Me

[ultratiger89]

I had an issue with surging, it only happened occasionally, usually when trying to get on plane, and started after my mechanic removed the fuel separator and what I believe is the fuel pump (pictured) six weeks ago. I could cruise at 3800 - 4000 RPM's no problem, but ramp it up to 4500 and it would start starving for fuel. I changed the separator, filter, and then yesterday pulled the barb screwed into the 90 on top of the fuel tank (I thought this was the anti-syphon valve but there was no ball and spring in it). So knowing that wasn't the problem, I checked the leads to the item in the picture and found that it wasn't plugged in. I never checked before because I didn't think the engine could run without it plugged in. I haven't run the boat yet to confirm this was my problem but I'm 99% sure it was.

This is the fuel pump right? Looks like it from the Mercruser Site. Don't know how I could run without it.

http://www.mercruiserparts.com/Show...=2333&bnbr=90&bdesc=FUEL+PUMP+AND+FUEL+COOLER

 

[VTSeaRay]

I had an issue with surging, it only happened occasionally, usually when trying to get on plane, and started after my mechanic removed the fuel separator and what I believe is the fuel pump (pictured) six weeks ago. I could cruise at 3800 - 4000 RPM's no problem, but ramp it up to 4500 and it would start starving for fuel. I changed the separator, filter, and then yesterday pulled the barb screwed into the 90 on top of the fuel tank (I thought this was the anti-syphon valve but there was no ball and spring in it). So knowing that wasn't the problem, I checked the leads to the item in the picture and found that it wasn't plugged in. I never checked before because I didn't think the engine could run without it plugged in. I haven't run the boat yet to confirm this was my problem but I'm 99% sure it was.

This is the fuel pump right? Looks like it from the Mercruser Site. Don't know how I could run without it.

http://www.mercruiserparts.com/Show...=2333&bnbr=90&bdesc=FUEL+PUMP+AND+FUEL+COOLER

I'm not familiar with this setup, but it sounds to me like the fuel was only being fed by pressure from gravity, and the fuel was able to keep up with it at lower RPM's, but when you increased your RPM's, it wasn't able to keep the flow going at the required rate needed for those higher RPM's and was in fact starving for fuel. The fuel pump would keep the pressure up for your engine at all RPM's.

 

[mistercomputerman]

I have two on each engine. One in the cool fuel box and the other mounted on the stringer. As far as I know, they are both fuel pumps.

 

[ultratiger89]

I have two on each engine. One in the cool fuel box and the other mounted on the stringer. As far as I know, they are both fuel pumps.

I assume this is the high pressure fuel pump as the outlet has tubing instead of hose. I would think the injectors need the higher pressure to even operate. I have the fuel pump on the stringer also, two actually, one for the engine and one for the generator. Guess that pump provided enough pressure to run the engine at mid range RPM's, I didn't think it could.

 

[my3sons]

newer motors are new to me this year with my 360, but I have been trying to read up. If I remember right, that is a "boost pump" and it pulls fuel from the tank and pushes it through the spin on water/fuel seperator and on to the "cool fuel pump". It is supposed to help the cool fuel pump as it may be overworked trying to draw fuel all the way from the tank, through the in-line filter, through the spin on water/sep. filter and then to the fuel rail and be able to maintain pressure. My guess might be that if it was not hooked up, the cool fuel pump was indeed unable to maintain correct pressure by trying to do the work all alone, thus you experienced poor performance. :huh:
p.s. If you include your engine model in your signature it would help, I asume you have a similar set up to me. take care

 

[ultratiger89]

If I remember right, that is a "boost pump" and it pulls fuel from the tank and pushes it through the spin on water/fuel seperator and on to the "cool fuel pump". It is supposed to help the cool fuel pump as it may be overworked trying to draw fuel all the way from the tank, through the in-line filter, through the spin on water/sep. filter and then to the fuel rail and be able to maintain pressure.

in the parts diagrams it doesn't show another fuel pump after this one. I have one that is on the stringer that is right on top of the gas tank that feed through the filter to this one. My guess this is the HP pump, and I would think the injectors needed the higher pressure to operate properly. Odd thing is that up to 4000 RPM's it ran fine.:huh:

 

[tdappleman]

Looks like the low pressure boost pump as previously stated. It may not show in some of the diagrams but I believe it was added to help with problems found during 'customer testing...' It may be the same pump added when a vapor lock condition was experienced as well.

 

[my3sons]

in the parts diagrams it doesn't show another fuel pump after this one. I have one that is on the stringer that is right on top of the gas tank that feed through the filter to this one. My guess this is the HP pump, and I would think the injectors needed the higher pressure to operate properly. Odd thing is that up to 4000 RPM's it ran fine.:huh:

Not sure about "pump on top of gas tank". there are soliniod valves there that turn on and off with the ignition switches so fuel can be drawn out of the tanks. I am going to step aside here because I am not sure of your set up and what motor you are running, and the last thing I want to do is give you bad/wrong info. I am willing to bet that you will be ok after reconnecting the leads to the pump. If you have the 5 liter bravo, the link below is what I am refering to
Good luck
http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr=884717&ivar=images/COMMON/1354.png&inbr=8093&bnbr=80&bdesc=Fuel+Filter+and+Boost+Pump%28BRAVO%29