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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 11052
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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My Sea Ray (carbureted Mercruiser 5.0L serial 0L072087)

Customer Question

My Sea Ray (carbureted Mercruiser 5.0L serial 0L072087) stalled from normal cruise with plenty of fuel, good oil pressure, good water temp, etc, no alarms. After checking fuel, oil, etc OK, loosened the fuel line into the carb and cranked without generating any fuel leakage at loosened fitting. Now troubleshooting the fuel pump. Getting no power at fuel pump quick disconnect with key in run position. Trying to trace where the power from the ignition switch is being interrupted; however, could use some help with electric fuel pump theory of operation, wiring, and related component locations.
JA: Sometimes boat issues seem like they'll be really complicated, but end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Is there anything else important you think the Marine Mechanic should know?
Customer: don't knw
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.

Hello. My name is Tan.

Do you have a volt meter to do some voltage tests? We need to check voltage at the fuel pump when engine is cranking. If engine starts does the voltage go away when you let off the key?

Do the gauges come on when key is in on position?

Customer: replied 1 year ago.
As i thought i indicated, we put a meter on the fuel pump qd in the engine harness and got no voltage with key in off or run positions. I'm trying to learn how to trace back from the qd to whatever devices upstream of the qd to find out where the power is being interupted.
Customer: replied 1 year ago.
To be clear, the engine will crank. It will not start. It does not appear to be getting fuel.
Expert:  Tan replied 1 year ago.

As I ask we need to test for voltage when cranking. Have you done that?There is a specific procedure to test this system. What you have done is not the procedure. I have outlined the procedure.Is there a reason you can't do the procedure I outlined?

Expert:  Tan replied 1 year ago.

The way this fuel pump works is it gets voltage from the start circuit when cranking then when it starts there is an oil pressure switch that comes on delivering voltage when you achieve oil pressure.

Customer: replied 1 year ago.
Got it. Ok, I'll get a second person unless I can rig and watch the meter myself. I'd like to get back after trying that and let you know what learn.
Expert:  Tan replied 1 year ago.

You can do this test right at the starter. With the use of a jumper wire. Jump from battery positive on starter to the yellow/red terminal. Check for voltage on the fuel pump purple/yellow or on the start solenoid on the starter.

In this diagram with jumper wire jump from term A to B and check voltage on D.

Customer: replied 1 year ago.
Roger. If I can get to that solenoid, I'll do so. If not, just use the key, right?
Expert:  Tan replied 1 year ago.

Correct. Or you can jump the start solenoid on top of the engine slave solenoid. Jump between the 2 large terminals this will crank engine. Test voltage at fuel pump.

Customer: replied 1 year ago.
Thanks. I'll be a while getting back to the marina into the engine compartment and tested. Will I still be able to reach you later in the day?
Expert:  Tan replied 1 year ago.

Absolutely. If you have voltage to the fuel pump and it doesn't run then the pump is bad. To test the pump apply voltage to the fuel pump purple/yellow wire with a jumper wire. If pump runs we have a voltage delivery issue. If it doesn't run the pump is bad replace the pump.

Post back with questions and findings.

Customer: replied 1 year ago.
Awesome. Talk later.
Expert:  Tan replied 1 year ago.


Customer: replied 1 year ago.
We have a voltage delivery issue. Direct wire to pump makes it sing.
Expert:  Tan replied 1 year ago.

Ok did you check for voltage on the fuel pump wire when cranking? Do you have voltage?

Customer: replied 1 year ago.
Tan, I'm really puzzled now. While cranking, I had 12v at D on the solenoid. Then, to my amazement 12v at the QD to the fuel pump. Thinking g we have a clogged fuel filter. Got dark on us. Scratching my head now.
Expert:  Tan replied 1 year ago.

Change the fuel filter then see if engine will start. If it starts check voltage at the fuel pump.

We have to verify we still have voltage to the fuel pump.

Customer: replied 1 year ago.
ThE fuel pump quick disconnect had 12v, and i heard it run earlier. Cranking is too loud to he as r it though.
Expert:  Tan replied 1 year ago.

Loosen the fitting at the carburetor. Watch for fuel.

Customer: replied 1 year ago.
Did that. Not a drop. Ergo, my filter suspect. Resuming in am. Tired, frustrated, and greasy as heck. Thanks for hanging with me.
Expert:  Tan replied 1 year ago.

Ok change the fuel filter. Fill the new filter with fuel before you put is back on. Then check for fuel at thew carburetor. I would connect voltage to the purple/yellow wire on the starter till you see fuel at the carb fitting. Then tighten the fitting crank engine does it start?

Talk with you tomorrow.

I'm on PST time.

Customer: replied 1 year ago.
Deal ! Thanks
Expert:  Tan replied 1 year ago.

Your welcome.

Customer: replied 1 year ago.
Ahoy Tan - you know, a new fuel filter can do wonders getting fresh fuel to the pump & carb - within a few 10-15 second cranks she fired up and purrs like a kitten - revved a few times, then let it idea while i cleaned up the boat for about 30 minutes - no issues - your electric checks got me pointed back in the right direction, away from the pump or solenoid where i was convinced the problem existed - only wish i had a schematic for the engine electrical to keep on the boat - not that i did not appreciate chatting with you - many thanks, ***** ***** thanks - Bingham
Expert:  Tan replied 1 year ago.

That's great glad I was able to help.

Here is a wiring diagram.

Please don't forget to positively rate my help as that is the only way I get credit for helping you.

Here is a direct link to me for future issues.

Thank you......Tan