low water pressure 2005 merc 280 hp

[benwilliamsjr]

just rebuilt engine after breakin 5000 rpm alarm goes off switched pump changed gear case new pump hooked water hose direct to copper tube gear case off to see where water is going changed pan gaskets pump is fine water is just dumping back in housing promarine gaskets with garden hose hooked to copper pipe 35psi very little water comes out of dump hoses or pressure gauge fitting with very low pressure is it wrong pan gasket I need help

[rjdubiel]

what is the part number for the base gasket you are using? 27-823142?

Before rebuild there was no issues? Is this a ROS or CON 280? Is this a complete factory stock 280 adapter plate? 1/2 inch water tube or 3/4? Where are you pulling the water pressure from? Do you have pictures of the adapter plate dump holes? They should be the two big dump holes in the adapter plate. When you put the hose on the copper pipe, you should have water spraying out the poppet dump hose, the heads, and water pressure fitting like crazy.

[benwilliamsjr]

gaskets for 260 280 from promarine dont know number 3/4 pipe 1piece adapter stock sport yes 2large holes

[25two.stroke]

Water pressure sender is probably bad causing it to not tell the ecm an accurate water pressure. See it all the time. Plug in a ddt and check the water pressure and see if it sounds right.

[rjdubiel]

I did not know the horn went off also, my horn must not work! haha. I just know it wont let it go past 5K if the sensor is not working on a CON ECM. ROS ECM don't care if the sensor is there or not. In fact I had a 280 with ROS harness and CON ECM and there was not a plug for the water pressor sensor on the ROS harness at all.

[25two.stroke]

I did not know the horn went off also, my horn must not work! haha. I just know it wont let it go past 5K if the sensor is not working on a CON ECM. ROS ECM don't care if the sensor is there or not. In fact I had a 280 with ROS harness and CON ECM and there was not a plug for the water pressor sensor on the ROS harness at all.

Yes

[benwilliamsjr]

I checked water pump housing is warped could this cause my problem

[gmorgan]

The exhaust divider plate gasket is not the same between the 260 and 280. Make sure you have the correct gasket.

[25two.stroke]

I checked water pump housing is warped could this cause my problem

This can, yes.
Also the divider plate gasket is different like Ben mentioned; even though the dividers are interchangeable.