5.7 L mercruiser Oil Pressure sending unit and fuel pump

[raftin]

Helping a friend with a 1999 Mercruiser 5.7L carb stern drive. Engine has had problems with the engine starting, running for 10 to 20 seconds and then dieing. This has been a chronic problem and it has been doing this for a few years and two marine mechanics have looked at the problem multiple times without resolution. I have installed a splice kit and a pressure gauge between fuel pump and carb to confirm that it is a loss of fuel pressure. Of course I have not been with him when it happens so I can not test the voltage to the fuel pump, but once I think I was able to replicate the problem and multimeter went to ~10V on starting and then dropped to 0V. I suspect the connection on the oil pressure sending unit is at fault. The connection seems to have some corrosion. I know one replaced the fuel pump. It appears the sending unit has been replaced also since the contacts appear new and I see a bit of corrosion on the oil pressure sending unit contact wires which I need to clean. (any tips on cleaning)

If it happens again when I am not there I have instructed him to look at the oil pressure gauge after it starts to confirm the guage says "0" and to then check/wiggle the wires on the oil pressure sending unit to see if it solves the problem. I don't have access to a schematic of the wiring to look at so I'm not sure I am missing something else.

I have also thought about having him "short" the 2 wires connecting the oil pressure sending unit if the above does not work to help diagnose the problem. It seems that the oil pressure sending unit drops to about 0.3 ohms after the engine starts running. (any advise here?)

After cleaning I have considered putting dielectric grease on the connector to try to cut down on corrosion, but I don't see any grease used in other areas.

Any one got any other ideas...

Thanks in advance!

Fortunately it has been a long time since I have posted anything and my old username is gone now!

 

[midcarolina]

Sounds like you are on the right track......... you can clean the terminals with a small wire brush or some emory cloth, a little dab of dielectric grease ain't a bad idea.

Make sure you also check the ground connections good also.........

 

[Bt Doctur]

What I have found happening is the electric fuel pump start to draw more amps as they get older or get water in them thru the fuel. The switch contacts cant handel this increased current and burn out. I replace the pressure switch and install a cube relay that powers the fuel pump.