Oil Pressure Switch 1999 mefi3 mercruiser 5.0

[josh_n_va]

Hello, my boat intermittently (about 1 in 10 starts) surges down in rpms almost dying and back up. Alarm beeps. Also, during plane it occasionally stalls as though fuel starved with a solid alarm. I replaced fuel water separator first with no improvement. Ordered a scan tool and it showed low oil pressure and low fuel pressure faults. My next step was going to be replacing oil pressure switch since I have read where it can shut off fuel which I assumed would show the low fuel pressure fault. Does this seem reasonable? I located this sensor low on the block on starboard side about mid way front to back. It is pictured. Is this the oil pressure switch related to the ecm or another sensor? If not, where would it be? I've seen pictures of some that are below the oil filter but my oil filter is different, mounted high with tubes running up to it on port side. Thanks so much!

 

[alldodge]

Howdy
Need a motor serial number

The sensor in the pic is a knock sensor

 

[josh_n_va]

Thank you I was afraid that might not be it. The sn is 0L340610

 

[kenny nunez]

The sensor should be near the oil filter.

 

[Bondo]

The sensor should be near the oil filter.

Ayuh,...... Or just behind the distributor,......

Those are the only oil pressure ports on a SBC,....

 

[alldodge]

The oil switch should be below the distributor at the rear of the block
It will have a single Blue/Tan wire

 

[josh_n_va]

Thank you! Is the oil pressure switch a reasonable culprit for the symptoms that I described?

 

[alldodge]

The oil pressure switch connects to the ECM, and does not go directly to the alarm. The switch can have a couple different faults types, a soft and hard alarm. The Bulletin 99-03 (revised 2000) will list how they work

Tried to upload but there is an issue. In short it can have a soft alarm below 3000 rpm (short beep, 3 second pause and repeat). A hard alarm above 3000 rpm solid alarm

Low fuel pressure at rail can cause alarm along with voltage below 9V

 

[josh_n_va]

Thank you! I also got a low voltage fault along with general warning #1 and general warning #2. I assumed maybe the loose voltage was from changing out the batteries. If the oil pressure switch doesn't take care of it then I will also replace the fuel pump. Thanks again!

 

[alldodge]

With low voltage I would start with connections, remove and clean, and most important are the grounds

 

[Fun Times]

Scan tool and it showed low oil pressure and low fuel pressure faults. My next step was going to be replacing oil pressure switch since I have read where it can shut off fuel which I assumed would show the low fuel pressure fault. Does this seem reasonable?

Just for better clarification purposes 'On your EFI system the oil pressure switch isn't directly tied into the fuel pump power operation...The oil pressure sender and/or switch only affects the warning horn operation on EFI's.... The oil pressure switch was designed to continue 12v power to the fuel pump on Carbureted engines after the engine has started and has/sees 4 or more psi of oil when working correctly....Should oil psi go under 4 psi, the fuel pump should turn off for safety purposes.

With all the codes you're seeing plus the warning beeps, may indicate a low voltage situation either intermittently or continually...Does your scan tool show you the Voltage while engine is running? Keep an eye on the 12 - 14 voltage ranges and start checking for dirty and loose power wires and battery cables all throughout the boat including under the dash area starting at the ignition switch.

Also just to know for sure you'll want to consider checking the fuel pressure to see where it's at before spending a bunch of money buying fuel pumps and senders/switches for possibly little reason that may not help much in this situation.

Does the 2 throttle body injectors seem to spray an even amount of fuel. https://www.mercruiserparts.com/bam/...31844/2704/110
https://www.mercruiserparts.com/5-0l...-0l012052-thru