Oil pressure gauge pegs to max

[Bmarler]

Thank you all for the suggestions and help. After many tests and repeat test and even though I swapped senders to wire harnesses with presumably positive results, I swapped senders to motors and now the stb side works and the port side does not.
Original stb side sender is faulty.
Now to find one.

Tranny pressure as well?

 

[The Dread Pirate Robert]

Yes

 

[Dougcole]

I just went through something similar to this on my Faria gauges. It's very frustrating as gauges can be super sensitive and there are multiple opportunities for shorts, especially if the gauges are daisy chained. With me it turned out to be BOTH bad sender wires and bad grounds.

It seems most of your focus has been on the signal and positive sides of the circuit. I scanned through the thread quickly and may have missed it, but have you tried running a clean ground straight to the gauge that is not working? Is there a ground buss close by that you can tap into? It really sounds like a grounding issue to me.

 

[MichaelD]

If the gauges on the dash are pegging, as you described, that's an indication that they are seeing zero impedance in the circuit, i.e. a short to the DC V supply (12 or 24 ). So, look for that.

I had that symptom, but in my case it was due to a shorted sender that was a new replacement for a failed sender. Had to get another and then it worked fine.

 

[mrfixit48]

Get a mechanical gauge or a oil pressure tester. About $25 for either on Amazon.
Temporarily replace the sender on the engine with high oil pressure. The gauge or tester should screw into the port where the sender is now. Then start the engine and you'll know the real oil pressure.

I have enjoyed a 55 year career as a Field Mechanic for Caterpillar and Komatsu and have owned a boat since I was 18. In all that time I have experienced countless faults of this type and the only real solution, if you want true readings, is to go with mechanical gauges. I agree they are a pain to set up but they either work or they don’t and it’s way easier to figure that out than electric gauges - way to many variables - corrosion, broken wires, degraded wiring, wiring that is too tightly secured which can cause heat build up, miss matched senders and so on. I currently own an Island Gypsy 36 with twin 6BTA 5.9L Cummins. I have mechanical gauges at the main helm and electric gauges on the fly bridge. The electric gauges are just for reference, not for accuracy. The mechanical gauges are the ones I rely on for relevant info for O/P and W/T