1996 merc 150 efi water pressure woes

[kramclrk]

Hello all, I am new to the forum and this is my first post but I have read tons of things here and learned alot.

I have a 1996 nitro savage 884 with a 96 merc 150 EFI OG396784 on a 6 in jack plate.the engine is having water pressure issues. It started after the third trip out this year. The issue is that at idle I was getting 5 PSI which is cool but as i get up on plane water pressure would build to 10 then suddenly fall to 0 then bounce around from zero to seven. I thought maybe the motor was to high so i dropped it to way below pad 5 inches below. problem was unchanged. I put it back on the trailer and backed it in to see if water pressure would flutter in neutral and it does. right at 1500 to 1700 rpms is when it starts. I disconnect the pressure gauge and at idle it has a steady flow of water out of the line. If I raise the RPMs the flow becomes irratic but does not increase. I tossed a poppet valve at it to see if that was the issue and replaced the water pump with a OEM kit last weekend. In a large tub in the driveway I now have 10 PSI at idle in Neutral which is right at 900 RPMs. When I raise the RPMs to 1500-2000 in the tub water pressure does not increse it falls again but not to zero only to 7 and then stays there. I am stumped on what it could be. If anyone has experienced this issue please give me some suggestions.

Thanks

 

[kramclrk]

Re: 1996 merc 150 efi water pressure woes

Mercury xr6 water pressure - YouTube

the link above shows basically what is happening.

 

[wired247]

Re: 1996 merc 150 efi water pressure woes

With the new pump in it you should try it in the water at speed before you get too worried about it. Mercury does make a diverter that helps water flow into the side intakes quite a bit. You might even have a water intake into the pump partially clogged. Try it in the water first .

 

[wired247]

Re: 1996 merc 150 efi water pressure woes

I'll go ahead and ask. Where is your gauge hooked up to?

 

[kramclrk]

Re: 1996 merc 150 efi water pressure woes

The gauge is hooked up at a t from a fitting going into the block between the heads. the hose it is teed into a hose that runs to the poppet valve. from my understanding this is the correct location to have it on the inlet side. Also I wont have a chance to get the boat in the lake till sunday to see if it is working after the new pump. living in the desert I got a two hour drive just to get the ramp.

 

[wired247]

Re: 1996 merc 150 efi water pressure woes

Yeah. OK. Thats what I was thinking you might have done. Don't do that. Your readings will be all over the place and are all over the place because of it. Hook it up to the exhaust divider or to the top of the heads or the top of the block near the open cooling water plenum over the exhaust chest. It will mean drilling a hole and tapping the hole for a 1/8" NPT fitting.

If you pull your exhaust divider you'll see a big hole into the water jacket that is about 1 1/4" or so wide that is located higher than the divider. You can run a drill through that to the outside and tap from the outside in. Or you could drill and tap from the outside in if you are careful. Its pretty much a stright shot 3/4" down from the top port side bolt hole. Thats where the factory puts the gauge water tap on the HP motors.