2004 Sea Ray 240 - No oil pressure on gauge

[sptjet90Reflexx]

2004 Sea Ray 240 Select
8.1L Mercruiser
SmartCraft System
240 hours
Bravo One

Took out the boat this year and after about 5 minutes of idle on the water, went to accelerate and the oil pressure dropped to 0 as well as an alarm indicating faulty sensor (if I recall its warning correctly)

Pulled boat out of the water and did some testing on the trailer.

Checked the connection at the sending unit and found no issues.
Verified again that oil was in the boat, at recommended levels.
Used an ohm meter and sending unit is reporting about 240-250ohms with engine off, drops quickly to about 80 or so when the engine starts. So I know I have pressure.

Both the analog gauge and the digital gauge inside the tachometer show Zero oil pressure. All other analog gauges on the multi-gauge are functional (fuel, engine water temp, voltage)

Attempted a master reset of the tach to see if it would clear up any issues.

Replaced the oil pressure sending unit with a Mercruiser OEM unit as the one in the boat did not appear to be OEM.

Tried applying better ground to the sending unit and saw no fluctuation in the gauges.

I have never had this issue before but it did happen right after having the boat in the shop to fix and outdrive leak. They said they re-aligned the engine so I'm wondering if they damaged a connection/nicked a wire.

Does anyone know where the blue sending wire goes? It appears to be bundled into the main harness behind the engine but the wiring diagram I have located does not indicate much.

Thanks!

 

[Scott Danforth]

oil pressure gauge sender and oil pressure switch for alarm are two different senders. if both are indicating 0 oil pressure, most likely you have an oil pressure issue as the only thing the two devices have in common is the block and the oil pressure

plumb in a mechanical gauge and check

if you have no oil pressure, then you may need to pull the motor to find out why.

 

[sptjet90Reflexx]

I'm working on getting a mechanical gauge, but based on the oil pressure sender changing resistance would that not indicate oil pressure?

 

[sptjet90Reflexx]

50 psi at idle with mechanical gauge and jumps over 60 with some throttle. So oil pressure is good.

Now need to determine why the gauges are not functional.

Any thoughts?

 

[sptjet90Reflexx]

I am unable to determine exactly where this light blue sender wire is going.

Does anyone have a wiring schematic?

 

[sptjet90Reflexx]

More research indicates the blue wire goes to the #8 pin on the harness that goes to the front of the boat. This is a white wire inside the harness with 3 other white wires.

This appears to be the sender for only the mechanical gauge and that there may be a second pressure sender located elsewhere on the block with 3 wires going to the ECU.

Does anyone know where this 2nd one is located?