Oil pressure incorrect

[Mp2379]

Hey All, I have a 1987 Nautique with a 351 PCM and am looking to fix an incorrect oil pressure reading. Looking for some help identifying the smoking gun.

BLUF:
1. Ignition on, engine off, gauge reads 60. (gauge is 0-80)
2. Turn engine on, gauge pegs at 80.
3. Remove sending unit from block, with wire attached, gauge reads zero, when sending unit is grounded to the block the gauge reads 60.
4. The oil pressure read at the block with a dial gauge reads 30psi when warmed up.

Any ideas where to start?

[bturner]

The easiest and obvious path would be to start by replacing the sender and seeing what happens. You could conversely find a replacement sender and gauge, get the specs for then and ohm out both the devices to see if they're in spec. The other area which seems to cause many issues is grounding. You could try bypassing the wring in the boat and directly attach the wires to the dash gauge to see if the symptoms change.

On a 35+ YO boat it would not surprise me if the wiring has been compromised.

[Mp2379]

Thanks for the input. I liked the idea of bypassing the wiring system and testing with known ‘clean’ connections. Once I got the gauge removed I heard something rattling around inside and out fell a coil of wire which appears to have come disconnected from something inside the gauge. Enough of a reason to replace. I will update once the new gauge is in.

[srock]

For reference, the senders do fail very inexpensive to replace. Less than $10 bucks.