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1993 5.0 EFI No Fuel Pump Power

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Nikokrzynowek

New member
Hey guys in new to the forums. Just picked up this beautiful 1993 190 horizon four wins with a omc 5.0l efi engine. I’m having a problem with the fuel pump. Underneath the fuel pump there’s a small connector with a few wires coming out of it. The 2 green wires going into the connector are my “hot” wires to get the pump to turn on. If I hold my power probe into the the green wires it shows no volts with the key on the on position or cranking and the motor won’t fire up. While I’m cranking my power probe goes from ground to barley any volts, but it shows that’s it’s switching off from a ground and trying to take some voltage. When I put 12 volts to the green wires I can hear the pump turn on. And then the boat will fire right up. If I keep constant power to those wires the boat will run forever. Instead of just making that into a on off switch for the fuel pump. I’d really like to have it working correctly. Does anyone have any ideas on what this could be. Or a wiring diagram or anything. All the help I can get at this point I’m trying to get this boat in the water for next weekend. Thank you guys!!
 
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Not sure about omc but most mercruiser use the feed coming from the starter. 2 small terminals on starter. One is start switch feed. The other is constant power for fuel pump. Not sure if this helps.
 
mechanicman said:
Not sure about omc but most mercruiser use the feed coming from the starter. 2 small terminals on starter. One is start switch feed. The other is constant power for fuel pump. Not sure if this helps.
Click to expand...

Im going to run outside right now and check the terminals on the side of the starter with key on and cranking. See if one of those isn’t putting out 12 volts or what the case may be there. Thank tou
 
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Nikokrzynowek said:
Hey guys in new to the forums. Just picked up this beautiful 1993 190 horizon four wins with a omc 5.0l efi engine. I’m having a problem with the fuel pump. Underneath the fuel pump there’s a small connector with a few wires coming out of it. The 2 green wires going into the connector are my “hot” wires to get the pump to turn on. If I hold my power probe into the the green wires it shows no volts with the key on the on position or cranking and the engine won’t fire up. While I’m cranking my power probe goes from ground to barley any volts, but it shows that’s it’s switching off from a ground and trying to take some voltage. When I put 12 volts to the green wires I can hear the pump turn on. And then the engine will fire right up. If I keep constant power to those wires the engine will run forever.
Instead of just making that into a on off switch for the fuel pump. I’d really like to have it working correctly.
I agree!
If you are in the US, USCG regulations require that the fuel pump's power be interrupted in the absence of engine oil pressure.

Does anyone have any ideas on what this could be? Or a wiring diagram or anything?
See if you can find what you're looking for here:
Use Google, not Google Chrome, and select ALL.

https://www.google.com/search?ei=z2...6......0....1..gws-wiz.......0i71.ulP-Qs9uVkY
Click to expand...

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mechanicman said:
Not sure about omc but most mercruiser use the feed coming from the starter.
Please note that the OP's engine and EFI are OMC. There may be similarities, but it would be best to stick with the OMC info.

2 small terminals on starter. One is start switch feed. The other is constant power for fuel pump.
There should be NO continuous power to the electric fuel pump.
The fuel pump's power will be available only when the system sees that the "start-bi-pass" circuit has been activated (during cranking), and/or when oil pressure is adequate to close the circuit.
USCG regs require this!
Click to expand...
 
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When I am cranking I get 40 pounds of oil pressure so I do not believe that’s an issue. But I’ll check the voltage coming out of the oil pressure swtich
 
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Nikokrzynowek said:
When I am cranking I get 40 pounds of oil pressure so I do not believe that’s an issue.

The oil pressure is not the issue........., it may be a faulty LOP (low oil pressure) switch.

But I’ll check the voltage coming out of the oil pressure swtich

This will be a N/O switch. In other words, the contacts (in the absence of oil pressure) will be NORMALLY OPEN.
Click to expand...
 
RicardoMarine said:
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So im out here tinkering with the boat now. Like I said in the first post when I initially crank the boat over it tears 1.2 volts at the green wire. For a few seconds after that nothing no matter if I’m cranking or not. Where is this oil pressure switch you’re talking about. And do you think that it could be the relay that the wires are all connected too???
 
On the GM SBC, the oil port for a LOP switch will likely be down/above the area of the oil filter.

And yes.... it could be a bad relay.
 
RicardoMarine said:
On the GM SBC, the oil port for a LOP switch will likely be down/above the area of the oil filter.

And yes.... it could be a bad relay.
Click to expand...

So on this sbf to the left of oil filter there’s the oil pressure sender that reads off the gauge on how much oil pressure the boat is receiving. Is that the same as what you are talking about or something different?
 
The helm instrument receives its data from an oil pressure sender. The sender is basically a variable potentiometer.

The LOP unit is an On/Off switch!
The contacts will be open with no oil pressure..... and will be closed with oil pressure!



.
 
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see page 443 in here , you have diodes that control the power to the fuel pump also the alt is what supplies power to the fuel pump or the ecm provides a ground to the relay to power the fuel pumps

 
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Bt Doctur, I tried several combinations of the URL replacing the "*'s", but no luck.

Would you mind posting the web address again, and perhaps this time put spaces between the characters (that are being blocked)?
We can then cut/paste it into our browser and then remove the spaces.
 
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Bt Doctur said:
see page 443 in here , you have diodes that control the power to the fuel pump also the alt is what supplies power to the fuel pump or the ecm provides a ground to the relay to power the fuel pumps

Click to expand...

When the boat was running it was only seeing 12 volts so my alt was either not charging it or there’s an electrical problem. I ordered a brand new alt and fuel pump relay. They should both be there tomorrow. So I’ll keep the tread posted on what happens. What does the alt do for the fuel pump tho? There’s only a small purple wire that goes to it. The fuel pump wires are green. How does that work?
 
Fixed!!! Not exactly sure if it was the alternator or the fuel pump relay. But now when I turn the key on the fuel pump turns on for a second. Starts right up and runs great no issues. Earlier when it wasn’t working every time I would hook up the negative cable to the battery I’d get sparks like it was shorting out. After the new parts it doesn’t do that anymore and everything seems to work perfectly now!
 
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