Fuel pump cutting out, 4.3 merc

[chknfrmr]

Good evening.
I have a 2003 4.3 mercruiser, carbureted engine. Three times now, my motor has suddenly died while running. It will crank over, but not fire. It seems like its out of fuel. The only way to get it to start is to jumper the fuel pump with 12 volts. Once I refill the float bowl, the boat starts, and will continue to run, no problem. The first 2 times, I was slowly cruising and thought maybe my oil pressure was too low due to prolonged running at low rpm. This evening it did it while pulling a tube, and running at 3000 rpm or slightly higher. My oil pressure was 40 psi pretty consistently at that rpm. Any thoughts?

 

[chknfrmr]

Good morning.
I have a 2003 Crestliner with a 4.3 mercruiser. The motor is carbureted, not fuel injected. Three times now, my engine quit on me while driving. The first two times it happened while slowly cruising down the river, low rpm's. Yesterday it happened while pulling a tube, higher rims. After it stalls, it will crank but not fire. It seems to be out of fuel. If I jumper the fuel pump, the boat fires up again, and continues running fine for the rest of the day. I thought maybe low oil pressure from driving slow, but that wasn't the case yesterday. Oil level in the engine is good. Any thoughts?
Thanks

 

[chknfrmr]

Sorry for the duplicate threads, I didn't think the one from last night went through

 

[alldodge]

There is a oil pressure switch (item 10) that sends power to the pump once the motor starts. It's located port side at rear of the motor. The gauge sender has one wire the switch has 2 wires

https://www.mercruiserparts.com/bam/subassemblydetail/42256336/28149107

 

[chknfrmr]

Would it fail intermittently? Once I get it running again its fine for the next several outings. Its happened once at the end of last season, once about a month ago and once yesterday.

 

[Scott Danforth]

Loose or corroded connections

 

[alldodge]

Might be a bad connection, and if it is than need to start cleaning contacts

A bad connection could be anywhere from the main harness to the key switch and back to the motor

 

[chknfrmr]

Thanks gentlemen. Gives me something to look for.

 

[Grub54891]

Not sure but I’d imagine that there is a fuel pump relay on that setup. I’ve seen it on others that have a bad or intermittent failing relay.

 

[Scott06]

Would it fail intermittently? Once I get it running again its fine for the next several outings. Its happened once at the end of last season, once about a month ago and once yesterday.

I could see the oil pump switch working intermittently for sure, could also see bad contacts. you would need to see if the pump is getting power when it dies and trace it back with a VM.

 

[Mark R.]

I don't think it uses the oil pressure switch to start. It only uses the oil pressure switch to stay running. During cranking, I believe power is applied to the fuel pump from the starter circuit. So the fact that it doesn't restart at all means its likely not the oil pressure switch. In other words, if the oil pressure switch were the problem, it would keep starting and then stalling.

 

[cwella]

Good evening.
I have a 2003 4.3 mercruiser, carbureted engine. Three times now, my motor has suddenly died while running. It will crank over, but not fire. It seems like its out of fuel. The only way to get it to start is to jumper the fuel pump with 12 volts. Once I refill the float bowl, the boat starts, and will continue to run, no problem. The first 2 times, I was slowly cruising and thought maybe my oil pressure was too low due to prolonged running at low rpm. This evening it did it while pulling a tube, and running at 3000 rpm or slightly higher. My oil pressure was 40 psi pretty consistently at that rpm. Any thoughts?

It sounds more like a fuel delivery issue than an oil pressure problem. Since jumping the fuel pump refills the float bowl and the engine runs normally afterward, I would check the fuel pump circuit first.

A few things to look at: the oil pressure switch that powers the fuel pump, the fuel pump relay (if equipped), wiring connections, and the pump itself. A failing oil pressure switch can cut power to the pump intermittently even with normal oil pressure. Also check the fuel filter, fuel line restrictions, and tank vent.

Since it happens at both low RPM and under load, I’d focus on why the pump is losing power rather than the carburetor itself.

 

[Scott06]

I don't think it uses the oil pressure switch to start. It only uses the oil pressure switch to stay running. During cranking, I believe power is applied to the fuel pump from the starter circuit. So the fact that it doesn't restart at all means its likely not the oil pressure switch. In other words, if the oil pressure switch were the problem, it would keep starting and then stalling.

correct and yes it would restart and then die after a min or two if oil pressure switch was dead. Could be anyone of several things that he needs to trouble shoot vs using the parts cannon.

I had my oil pressure alarm switch working intermittently when I got my boat. It was a handymans special that had never had an oil change (10 yrs, 38 hrs) before someone cracked the block. For the first season or maybe two when staring the buzzer only went off intermittently, suspect there was some sludge in the switch which I moved over to the new long block.

 

[nola mike]

Not sure but I’d imagine that there is a fuel pump relay on that setup. I’ve seen it on others that have a bad or intermittent failing relay.

No relay on there.

I don't think it uses the oil pressure switch to start. It only uses the oil pressure switch to stay running. During cranking, I believe power is applied to the fuel pump from the starter circuit. So the fact that it doesn't restart at all means its likely not the oil pressure switch. In other words, if the oil pressure switch were the problem, it would keep starting and then stalling.

Correct, though who knows with an intermittent problem

EDIT: my thread on an intermittent oil pressure sender failure

Oil Pressure Sender failure modes?

TL;DR: What would cause an oil pressure sender to fluctuate between reading correctly and reading zero? Been chasing an oil pressure gauge/issue all summer. Mercruiser, standard analog sender/gauge. It will run fine for long stretches of time, steady at 60 psi, then drop to "zero" (actually...

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