Fuel pump and alternator question

[DrDockinc]

Good morning gentlemen,
I am new to forums all together. This is my first post ever, so I hope I'm doing this correctly.
To jump right in to things I will try and explain as to the timeline and details of what happened.

Boat Specs:
5.7 GS PEFS
Serial #4012049075
(3869058)

Symptoms:
Boat had run fine earlier in the day. After launching at a new ramp headed to another job the motor started to sputter and die as soon as we started to accelerate. I checked the screw on fuel filter at front of engine and found it to be full, however the gas was ever-so-slightly whitish cloudy. Emptied it and screwed filter back on empty. Tried starting engine and was successful at restarting after slightly longer cranking as would be expected. Repeatedly the engine would start as it always has but would stutter and die within 30 seconds or less. At one point I had engine in neutral and was able to get it revved up to 3k or so when I noticed smoke, immediately a saw some faint red intermittent glow from inside the alternator housing. Once engine stopped there was indeed wisps of smoke exiting the alternator as well as it was fairly hot to the touch.
Fortunately we were able to get the engine to run long enough to load back on trailer. I was able to purchase a replacement fuel pump but am not excited about swapping it out until I am 100% certain that is the problem.

Once back at shop and on muffs I did some testing. I found that the fuel pump doesn't run with ignition key on while engine is not started. Not sure if that is normal. However I disconnected the fuel line at the carb and tried starting engine and I did find that the pump put out significant fuel while starting the engine but immediately quit pumping as soon as engine had started and ignition key released to run position. Thus the reason the engine would always start and run for short periods of time before dieing.

Here is my concern/question. I find it hard to believe that the alternator and fuel pump problems are independent of each other. Its highly unlikely that they would both fail at the same time. But I just cant wrap my head around why they would be linked together. I personally would like the piece of mind knowing that I could limp the boat back to shore on battery power alone. I find it inconceivable to believe that I would be stranded because of an alternator failure. Am I correct in my hunch that the two are somehow related? I called my mechanics and they said that the pump should run as long as there was sufficient battery power. I can tell you that there is more than enough juice available to power the pump.

I'm hoping you guys can help me out here. Any suggestions?
Thanks so much,
Scott

 

[alldodge]

Howdy

Sounds to me your issue may just be the alternator. If it is shorting out then there is more current then normal being drawn and causing a low then normal voltage on all components. Could be there just was barely enough to keep the relay engaged to keep the pump running.

The fuel pump gets its power in two ways, one while the engine is cranking, when started power is removed. The engine has enough fuel in the carb to keep it running for a bit while oil pressure builds up. Once oil pressure builds up, the oil pressure switch closes and power is sent through the switch to the fuel pump.

gas was ever-so-slightly whitish cloudy

Might have some water mixed in with the gas. If this made it to the carb you will have some real issues keeping it running

 

[bruceb58]

They are related. The L2 terminal of the alternator is what turns on the relay that drives the fuel pump(not an oil pressure switch). The other way the relay is turned on is a wire that comes from your starter circuit that allows the pump to run while cranking. This is used to make sure the pump only runs while the engine is running. In an emergency, you can pull the relay and jumper 2 of the terminals(87 and 30) to power the pump.

Needless to say, your pump is fine.

go to page 143 here(7-43)
http://boatinfo.no/lib/volvo/manuals...lect.html#/142

You should replace your fuel filter and you should never dump it out and screw it back on. When you dump it, some of the contaminants from the "IN" side of the filter will get into the "OUT" side of the filter and you now allowed some previously filtered junk to go up to your carb.

BTW, you need a new mechanic that is familiar with Volvo.

 

[Maclin]

I just feel the need to align the information here regarding the power circuit that feeds the fuel pump. What bruceb58 posted is correct for a Volvo, and is why the issues in your case are probably just one issue.. Now on Mercs, the oil pressure switch method is in play, so different troubleshooting is needed. Between the two the same end result is achieved, fuel pump is only powered when engine is running (or during cranking).