Mercruiser Won't Stay Running Due To Previous Low Oil Issue?

[H231]

I have a 5L Mercruiser (around 2000) with a 2 barrel carburetor. Serial # OL359879. It developed a hole in the oil sender unit which ran the engine low on oil. As a result the oil pressure dropped and the engine shut off. I replaced the oil sender unit ( with the single blue wire) . Refilled the oil and started the engine. Oil pressure was reading fine both at idle and higher speed. However after 30 sec. the engine completely stops. Tried half a dozen times with the same result. It seems like the carburetor gas is burning but is not being replenished. Went to local dealer he thought it might be the oil sensor and advised to bypass it to see. He said that the oil sensor ( with the 2 purple wires) will have the fuel pump run once the oil pressure gets high enough. But when I connected the 2 wires that go to the oil sensor it did not have the desired effect to keep engine running and it shut off after 30 sec. as it did before.I've since asked if there were any other sensors and was told no. Although this may be a separate issue from running the engine low on oil, it sure seems to be related. I've never had any issues like this before. Please help I need to get the boat out of the lake!​

 

[Scott Danforth]

your motor uses an oil pressure switch to keep the fuel pump running after you start the motor

use the schematics in the manual to trace where your problem lies.

 

[H231]

Thinking that it was the sender unit, I direct connected with a wire to bypass that switch. However there was still the same issue. This all started with low oil pressure. Is there another switch somewhere? Any further suggestions are greatly appreciated.

 

[H231]

Fuel pump issue? If I hotwired the fuel pump from the connector on top of the engine should I be able to start up the engine? Would there be any issues with doing that? I've got to get this out of the water soon.

 

[Scott Danforth]

get the manual for your specific serial number and follow the schematics. dont try to bypass anything to get on the water soon. that is how boats blow up.

the fact that the pump runs when cranking means that its not the fuel pump.

 

[H231]

Thank you. Ok so that's off the table. Any thoughts about what else it might be? I've got the manual but I am perplexed as to where to go from here.

 

[Rick Stephens]

Power comes from the ignition switch, to the oil pressure switch, then to the fuel pump. Turn the key on (but don't crank the engine) with it wired as is, and use a 12 volt test light to see if there is power to one side of the oil pressure switch. If not, you found your issue is the source power.

If you do have power, turn the key off, connect the two wires together bypassing the switch, turn key on but don't crank. You should hear the fuel pump spinning. If not, then you have a problem in the wiring going from the switch to the pump.

I am assuming the pump is good since it seems to prime the carburetor when you crank the engine, enough for 30 seconds or so.

 

[H231]

Hi Rick, thank you for your suggestions. Just got to the boat and tried what you suggested. There is no power coming to the switch on either wire. Of course because of that there is no power coming to the fuel pump. The only wiring schematic I could come across was for my engine but it was for a fuel injected engine and mine is carbureted.

My next door neighbour came over and said that it was my electronic module which is a DENSO131800-7071. He said that it likely needs to be reflashed. Does this sound like it might be a solution?

Your help and the help of those on this forum is much appreciated!

 

[Bondo]

and mine is carbureted.

My next door neighbour came over and said that it was my electronic module which is a DENSO131800-7071. He said that it likely needs to be reflashed. Does this sound like it might be a solution?

Welcome Aboard,...... No, it doesn't,...... Yer problem is the wirin' from the key switch to the oil pressure switch,.....

That ignition module only controls the ignition,.....

 

[H231]

Thanks, Bondo. I guess that is a good thing? I've tried everything I can. It all comes from running out of oil. I couldn't find a fuse that would explain the problem. It's all a tightly wound harness which I am reluctant to cut apart. I've never had a problem with this before the oil pressure went low.

Thanks all!

 

[Bondo]

Ayuh,..... Before ya open the harness, check at the key switch, 'n at the cannon plug where the boat harness meets the motor's harness,.....

 

[H231]

I already did both of those things to no avail unfortunately.

 

[H231]

Any other ideas before it goes to a dealer? $$$$$