Oil pressure sender

[Deepwtr]

I’m sure a dumb question, but which oil sender on a 5.7 Merc is for the gauge? There is one under the starboard exhaust manifold and one back behind the distributor.

 

[Scott Danforth]

the one back by the distributor is normally for the gauge. it is bell-shaped

the switch for the alarm is usually in the side of the block. it would look like a glorified hex nut with connector on the end.

 

[alldodge]

This is the type for the gauge

 

[Deepwtr]

Yeah that’s what I would have thought. Mine doesn’t look like that. Here is what is on the engine now. The wire is off on purpose.

 

[Scott Danforth]

keep in mind that Mercruiser may have changed the locations around. what you are showing is the switch for the alarm, and the wire color confirms.

the wire colors are standard

light blue is oil pressure gauge sender
blue with brown stripe is oil pressure switch

 

[alldodge]

Look port side down by the oil pan

 

[Deepwtr]

On the port side? Ok I’ll see what I can find down there. I have one on the starboard side under the manifold, but it has a 2 pin delco type connector on it.

 

[alldodge]

Would need to see the connector, the only one I can think of on the starboard side under the manifold is the knock sensor, and it is a large one wire connector

 

[Deepwtr]

Ok, one saga solved, one deepens. I finally found the oil pressure sender, it was back by the oil filter.

I could confirm that wire there was for the gauge by pulling it on and off making the gauge move. However, the thing that blows me away was there was a black wire that comes from up by the ECU and was also connected to the sender. As soon as I removed that the gauge went down to zero.

So, it begs the question, is that just a ground wire for something? I pulled it up and it comes out of the harness right by the ECU.

It is a nice covered wire so it is supposed to be part of the wiring, it wasn’t something someone scabbed in other words.

 

[Bondo]

So, it begs the question, is that just a ground wire for something? I pulled it up and it comes out of the harness right by the ECU.

Ayuh,..... Sometimes there's a screw up through the bottom of the distributor for a ground wire,......

It for sure don't go to the o p sender,....

 

[alldodge]

and was also connected to the sender. As soon as I removed that the gauge went down to zero.

Post pic please of where it was connected

 

[Deepwtr]

It was on the same screw as the oil pressure sender wire. In my head it makes sense to me as to it being a ground it basically grounded out the sender wire which is why the gauge pegged out as soon as the key switch turned on. I took a picture of the ground wire this morning before I left the house, but I need to figure out how to make the size smaller so I can post it on here.

 

[alldodge]

It was on the same screw as the oil pressure sender wire. In my head it makes sense to me as to it being a ground it basically grounded out the sender wire which is why the gauge pegged out as soon as the key switch turned on.

No need to post the pic anymore, you found your problem (which we didn't know originally) and as Bondo pointed out

 

[Deepwtr]

So, tonight I felt all around the distributor and I couldn’t find any screw that would have made sense to be a connection for that rogue wire. Will it make sense to just tape it up, tuck it away and call it good?

I’m assuming the ECU is grounded itself elsewhere and this doesn’t need to be connected to the block ground?

 

[alldodge]

It probably will be just fine doing that, and may have been for a ground to a Mercathode system, but in any case its a ground co it can be left hanging, or could find a place to fasten it to. Not going to hurt anything grounding it, and may help