mercruiser 5.0 MPI fuel pump issue(s)

[dogfish1]

Ok I have a problem with my stbd. engine and will start with the basics. It is a 2003 5.0 MPI with bravo 3 drive, engine serial number is M366509.
The engine will give the infamous and ominous 2 beeps every minute warning. Occasionally it starts beeping like crazy and all the gauges go to zero, rpm, oil, temp, trim, all gauges associated with that engine. The engine runs fine at idle and even underway but will give the two beeps. Also the fuel pumps, electric, run continuously on that motor, even when it is turned off.
My initial thought is there must be a pressure switch that should be shutting off the electric pumps. Is there a fuel pressure switch on this engine?

 

[Fun Times]

Re: mercruiser 5.0 MPI fuel pump issue(s)

Hi there, no there is no pressure switch that shuts off the electric fuel pumps, that is controlled by the ECM.

Judging by your description, it sounds like you may have either a loose or corroded ground or power wire/cable somewhere such as the battery or on the engine wiring harness or connector.

I would suspect your problem may lie within the main wiring harness connector called the cannon plug that plugs into the engine coming from the dash of the boat. It is black in color that looks rubbery.

With the key on, you will want to start carefully wiggling all wires/connectors around looking for the ignition system to go back to normal operation. Also disconnect the cannon plug located typically near the rear of the engine and inspect it. It should be held on with a hose clamp or wire tie.

Let us know what you find, Good luck

 

[dogfish1]

Re: mercruiser 5.0 MPI fuel pump issue(s)

Hi there, no there is no pressure switch that shuts off the electric fuel pumps, that is controlled by the ECM.

Judging by your description, it sounds like you may have either a loose or corroded ground or power wire/cable somewhere such as the battery or on the engine wiring harness or connector.

I would suspect your problem may lie within the main wiring harness connector called the cannon plug that plugs into the engine coming from the dash of the boat. It is black in color that looks rubbery.

With the key on, you will want to start carefully wiggling all wires/connectors around looking for the ignition system to go back to normal operation. Also disconnect the cannon plug located typically near the rear of the engine and inspect it. It should be held on with a hose clamp or wire tie.

Let us know what you find, Good luck

I will check the wiring harnesses as you suggest, I will also check the ignition key switch. I am curious, what shuts off the fuel pumps? Usually they run for about 5 seconds when I turn the key to run then shut off until I turn the key to start.

 

[Fun Times]

Re: mercruiser 5.0 MPI fuel pump issue(s)

I will also check the ignition key switch. I am curious, what shuts off the fuel pumps? Usually they run for about 5 seconds when I turn the key to run then shut off until I turn the key to start.

Good idea on the key switch, I was going to mention that earlier as well but slipped the mind. From your description, it does seem like it is acting as if someone was turning on and off the ignition key very quickly.

Again, the fuel pump is controlled time wise by the ECM turning on and off the fuel pump relay.

 

[dogfish1]

Re: mercruiser 5.0 MPI fuel pump issue(s)

It looks like the problem is a bad fuel pump relay. When I pulled it off its bracket the fuel pumps stopped running. I went and turned the ignition to on and the pumps cycled like they should. Went for a short run and the problem returned. When I got back to my mooring the pumps were running continuously again. When I pulled the relay again the pumps continued to run. I disconnected the relay from the wiring harness and smacked it a couple times reconnected it to the wiring harness and all was good again.
I will buy a new relay and install.
Thanks for the guidance.

 

[dogfish1]

Re: mercruiser 5.0 MPI fuel pump issue(s)

I just got the relay, it cost $31.24. The part is nothing but an omron relay, the same one sells for $4.90 from digi key. The parts mark up pisses me off!

 

[dogfish1]

Re: mercruiser 5.0 MPI fuel pump issue(s)

I just got the relay, it cost $31.24. The part is nothing but an omron relay, the same one sells for $4.90 from digi key. The parts mark up pisses me off!

So we were all set for a trip over to Long Island, we got as far as the mouth of the CT river and the stbd. engine started back firing the alarms started ringing and finally the engine died. Restarted it and headed back in. Today I went looking for a loose connection and found the power connection on the starter motor was loose. Tightened that up, several flats on the nut and everything is running great. I think I will double nut this connection!

 

[Fun Times]

Re: mercruiser 5.0 MPI fuel pump issue(s)

I'm happy to hear you were able to find the problem and everything seems to be back to normal. I had a feeling it would be something like that. Thanks for the update, Happy boating.