Merc. 5.7 dies after 15-20secs

[lfw2068]

I have twins 2001 Merc 5.7 L carburatror, one engine starts fine but dies after 10 to 15 seconds. During this period I can accelerate up and down but stills dies after 10 to 15 seconds. I do not know if the problem is electrical or carb related. I currently have the boat out od the water.

 

[Haut Medoc]

Re: Merc. 5.7 dies after 15-20secs

My guess is fuel related.....
There is a switch that is connected to the fuel pump that is related to the oil pressure.....
When this switch goes bad, it will kill the fuel pump....
You need to jump the switch & see if it corrects it...
Then replace the switch....
Don S recently posted a pic of where to find it.....​

 

[Don S]

Re: Merc. 5.7 dies after 15-20secs

There is an oil pressure switch (not to be confused with the gauge sender) on the port side of the engine, just below the #7 spark plug. It has 2 wires going to it. The switch is there to prevent the fuel pump from running when the engine is not running. When starting, the fuel pump is powered by a connection on the starter. That is why it will always restart.
To test the switch, just disconnect the 2 wires going to it and connect them together, or connect them with a jumper wire. With the ignition switch in the run position and the engine off, you should hear the pump run. You can even run the engine to verify it will keep running.
This is also a good thing to know and do if the switch fails while you are out on the water and need a way to get home. An emergency connection only.

Click Here for a wiring diagram of the fuel pump.

 

[Fishermark]

Re: Merc. 5.7 dies after 15-20secs

Not to argue the point, but just to be clear - isn't the #8 spark plug on the starboard side? If so, is the switch on the port side, under #7, or the starboard side under #8? Or am I completely backwards myself??

 

[Haut Medoc]

Re: Merc. 5.7 dies after 15-20secs

I would guess that he means #8 on a GM.......
That would be starboard.....
I could see Don getting port & starboard backwards....
I don't think he would do that on #7-8 plugs...... ​

 

[Don S]

Re: Merc. 5.7 dies after 15-20secs

I don't think he would do that on #7-8 plugs......

Wanna Bet?

Did an edit :redface:

 

[Haut Medoc]

Re: Merc. 5.7 dies after 15-20secs

Wrong again!....:redface: ​

 

[lfw2068]

Re: Merc. 5.7 dies after 15-20secs

Thanks I will try it today and get back to you.

 

[lfw2068]

Re: Merc. 5.7 dies after 15-20secs

I used the jumper and the engine runs fine. I have oil pressure in the gauge, can you let me know what is the purpose of the oil pressure switch? I guess if I have oil pressure the sender is sencing pressure and I should not worry about the engine not lubricating properly.

 

[Don S]

Re: Merc. 5.7 dies after 15-20secs

Good Gawd Man, read my first reply to this thread. I answered both questions before you ask.
The oil pressure sender that shows on your gauge does NOT have anything to do with the oil pressure switch that operates the fuel pump.

 

[lfw2068]

Re: Merc. 5.7 dies after 15-20secs

Admiral, I was worried that I might be runing the engine with no proper lubrication, but since the gauge shows oil pressure I guess I do not need to worry. I will replace it this week.

 

[Don S]

Re: Merc. 5.7 dies after 15-20secs

Admiral, I was worried that I might be runing the engine with no proper lubrication, but since the gauge shows oil pressure I guess I do not need to worry. I will replace it this week.

You need to replace the oil pressure SWITCH that controls the fuel pump. NOT the oil pressure SENDER that shows oil pressure on your gauge. They are 2 completely different items. So think about what you ask for. They are not the same thing and they are not interchangable.

 

[SuperNova]

Re: Merc. 5.7 dies after 15-20secs

As carlos Mencia would say "dee dee dee"

 

[Fishermark]

Re: Merc. 5.7 dies after 15-20secs

By the way, to answer your question, as I understand it the switch is a safety feature. The switch is designed to give power to your fuel pump only when the engine is running, (when there is oil pressure present). That way you won't be spewing gas all over the place in case of a leak and the engine isn't running... or something like that! There is a bypass power to the pump for the 15 or 20 seconds at first start up.

 

[Don S]

Re: Merc. 5.7 dies after 15-20secs

There is a bypass power to the pump for the 15 or 20 seconds at first start up.

That bypass is from the start solenoid on the starter, has no time limit. If the starter is engaged, then the fuel pump is on.
The ONLY time limit on a fuel pump running is on EFI engines, and lasts for 2 seconds. Nothing in the 15 to 20 second range.

Everybody needs to understand how the system works, not just guess at it.
Look at the wiring diagram I posted. Look at where the initial power to the fuel pump is coming from. And you have to know how switches work, how electricity works, and how the starter solenoid works to understand what is going on. If you don't understand one of those elements, then you don't understand the system.