Fuel pump

[Randy Lovelace]

4.3 merc alpha one drive 1998 model
This boat is new to me, just bought this week. When i turn the key on
i can hear a small noise in engine compartment. It sounds like an electric
fuel pump. I can't tell where it's coming from but i can feel a slight vibration
when i touch the metal fuel line. Is this what it is? Should it cut off when
pressure is reached? It doe's not cut off it keeps running as long as key is
on. AM i concerned about nothing? It is not the blower.
Thanks in advance for any replies.
Randy

 

[Maclin]

Re: Fuel pump

It would be best to post the serial number of your engine to get more focused answers.

In general though, an electric fuel pump should not run constantly with just the key on and the engine not running.

A carbed engine will only get power to the fuel pump during cranking via a bypass circuit, and then once started there is an oil pressure safety switch that only lets the fuel pump have power if oil pressure exists, i.e. the engine is running.

On computer controlled efi type engines the fuel pump will flash on for just a second or two to build pressure in the efi then it will shut off and not run again until the engine starts.

I would be concerned that on yours a problem with the oil pressure switch existed at one time and it has been shunted to run all the time, or something similar to this.

 

[Bondo]

Re: Fuel pump

AM i concerned about nothing?

Nope,...

That's a legitimate Issue,+ needs to be dealt with, for the reasons stated by Maclin...

The serial # will be Best,.. But just knowing Carbed, or EFI will Help....

 

[Randy Lovelace]

Re: Fuel pump

Serial # 0L071917 Not EFI
I can't start engine because it's winterised but the oil pressure gauge
does move a little when the key is turned on, so there is power to
the gauge. Is this a 1998 engine?

 

[Bondo]

Re: Fuel pump

Ayuh,...

It appears that the Low Oil Pressure Switch has been By-passed....

Check it out,...
It's mounted down low, port-side, mid-way along the Block...
Right next to the oil pressure Sender....

 

[Maclin]

Re: Fuel pump

The oil pressure sending unit for the gauge is a separate item from the oil pressure safety switch, so the needle movement you see on the gauge is almost surely not related to the fuel pump circuit.


That system should definitely not fire up the fuel pump with just the key on. You have inherited a previous owner's fix, and it is fundamentally unsafe without the oil pressure safety switch in the circuit.

There may be another switch on the dash or close somewhere, not stock, that controls power to the pump. Some have had problems with the carb not filling with fuel to their liking so they have wired in a bypass. When that is done the switch needs to be a momentary button or spring loaded lever type switch so it is only on when the operator is hitting the switch. Maybe they did this but used a regular switch and it is on now. It is more likely in my opinion that the oil pressure safety switch failed and they have wired across the oil pressure safety switch so the pump runs anytime the key is on.

I looked in the link below to Doug Russell catalog under Mercruiser and then 4.3l GM 262V-6 1998 and similar listings and the s/n OL010044 and up shows up so I would hazard a guess that it is a 1998. Others on this board can decipher the s/n further, but it is definitely a carbed engine and if that noise is the fuel pump then there is a problem somewhere.

http://dougrussell.com/partscatalog/index.cfm

 

[Maclin]

Re: Fuel pump

I agree with Bond-o, I was typing while he posted, good stuff.....

 

[Randy Lovelace]

Re: Fuel pump

Thanks for the info.
How do i check this switch or do i just need to replace it?
btw my manual should be in tomorrow.

Randy

 

[chiefalen]

Re: Fuel pump

If in fact the pump was hot wired there is a very simple way to find out.

Simply remove the hose going to the carb and turn on the switch for a few seconds, you can put that end you removed into a small clear container.

Leave the switch on for 30 seconds or quick go over and see if fuel is coming out.

And quick turn the switch back off.

Wola now you know if it's the pump or something else.