Penta 4.3 Fuel Pump issue

[dnardella]

I have what I believe to be fuel pump issue. My penta 4.3GL (Model 4328PLKD) on a 98 four winns has periodically quit running with no repeatable cause. This issue has been ongoing for 2+ years. Initially I thought it was the relay switch for the fuel pump. I have replaced three of them and after replacing the relay switch it runs fine for some length of time. The latest relay was good for about 6 months. However, it quit last night again. I keep a spare "jumper wire" on the boat the bypass the relay switch to turn on the fuel pump manually which gets me back to the dock. The only commonality to the problem is that when the system is completely cool, I am able to stick any of the "bad" relay switches back in the harness and the fuel pump fires back up and the engine runs again. I also feel like it has never quit on a full tank of gas. The tank was about 1/4 full last night when it quit (8 gal/32 capacity).

I am unsure about a few things though. Is the relay switch supposed to flip power from the electrical system to the oil pressure (which has always been pretty stable between 50-60 on the gauges) to reduce load on the alternator/battery? Is the fuel pump supposed to run continuously even after pressurized. I have been able to work around the problems by replacing the switch and then bypassing the relay if it fails, but I would really like to get this fixed correctly.

 

[bruceb58]

Re: Penta 4.3 Fuel Pump issue

The fuel pump relay gets energized by an alternator output through a diode. Maybe you have a bad connection somewhere or your alternator output is flakey. I would try to measure the voltage at the output of the alternator L2 terminal to see what voltage it is.

 

[Don S]

Re: Penta 4.3 Fuel Pump issue

I am unsure about a few things though. Is the relay switch supposed to flip power from the electrical system to the oil pressure

Mercruiser uses an oil pressure switch, Volvo doesn't. So oil pressure has absolutely nothing to do with your system.

You may be having alternator problems. If the alternator gets hot and stops working for some reason, then your fuel pump would stop as well. Since that is where the fuel pump relay gets it's power from.

 

[dnardella]

Re: Penta 4.3 Fuel Pump issue

Thanks for your thoughts so far. The alternator was putting out 13.8v to the green wire leading to the fuel pump at operating temperature (running for about 20 minutes at about 3000 rpm). I bought a new relay, but put the old one back in and it ran without an issue for that time. I did notice a very slight loose connection in the wires going to the fuel pump itself, and tightened them down. There was no corrosion on the connections. I don't think the pump was disconnected, because I was able to bypass the fuel relay and the pump worked when it appeared the relay failed.

One other item to note, I filled the tank up completely, but it stall had about 8 gallons left before refilling. Any possibility the 1/4 tank of gas caused a low fuel pressure issue thereby starting a series of events leading the relay to quit working? I am stetching here, but feel like the full tank may have something to do with better performance. Midsummer heat and less than 1/2 tank of gas are the only consistnecies to the relay failure that I have seen to date.