Sea Pump / Block Pressure Fault Code

[kt_maxum]

Hi All,

My Mercruiser 496 MAG went into guardian mode on me several times today. I had been running the engine for about 15 minutes after leaving the marina. I had the boat up on plane at 3,800 rpm for about 5 minutes, then slowed down to about 1,800 rpm and the guardian mode gave a constant beep.

I limped back to the dock and took readings on a Rinda Techmate (which I'm still learning to use....). The "freeze frame" data showed "Fault 3, Sea Pump / Block Pressure Low". The block pressure at the time the guardian kicked in was 0.3 psi (see photos).

Back at the dock I ran the engine at idle and took live readings. At idle the block pressure was 43.4 psi (which the code reference I have says is the "default" reading when sea pump psi is low - see last photo).

The raw water pump is new last season, as is the impeller.

Any suggestions? Possible bad sensor? Some sort of water intake blockage?

The port and starboard coolant temperature reading on the Rinda (I assume it's the temp of the risers?) while at idle was quite different (port was 107 F, starboard was 78 F), so I'm wondering if the port side is overheating due to poor water pressure? Overall coolant temp reading was 165.

Thanks,
Ken

[shrew]

if you have Bravo III outdrives, then the intake hose running from the pickups through the transom assembly can get crushed from aluminum corrosion and reduces waterflow.

If this is the case, then there are two solutions.

1) REplace the Transom assembly

OR

2) Install a through-hull pick-up, sea-cock and sea strainers. Then run a hose from the sea strainer to the raw water pump. Finally install a drive shower on the outdrive to cool it from the outside since there won't be cooling water running inside to cool the outdrive any longer.

[mmwjr]

Those temperature readings are all normal, are they current readings or data that was saved? If current I would take the boat out again and see what the readings are when the fault occurs. As shrew said the transom hose is know for blockage on Bravos.

[kt_maxum]

Thanks Shrew & Mike.

The sterndrive is a Bravo III X. The temperature readings were current (i.e. they weren't taken when the fault occurred). I took them a few hours after I returned to the dock and had the engine idling. The high PSI reading while the boat was at idle seemed odd to me. It also stayed constant and didn't change when I throttled up the engine in neutral.

I'll definitely take the boat out again and check the readings when the fault occurs. Will post the results as soon as I can. I'm also planning to swap the water pressure sensor in the hope it's some sort of bad sensor issue.

Cheers,
Ken

[kt_maxum]

I may have solved the issue......I ran the engine at the dock again and the block pressure at idle still read 43.4 and wouldn't change. I ran the engine with the sensor cable disconnected and got 0.1 psi. Figured the cable works but the sensors bad. I swapped it with an older one I had and psi at idle was 9.5 and about 22 at 2,000 rpm. Didn't get any alarms on pressure and the temps all held steady after the engine fully warmed up.

The pressure still seems a bit high based on what I read on old posts but the comments varied widely - is there a correct range for the 496?

The sensor I installed was one that was measuring the oil pressure that I pulled last year thinking it might be faulty too. I might buy a brand new sensor and see if the readings change.

Thanks,
Ken

[mmwjr]

I don’t know but under Documents there is the Mercruiser manual for your engine so you should look to see what it says.

[shrew]

Originally Posted by kt_maxum

I swapped it with an older one I had and psi at idle was 9.5 and about 22 at 2,000 rpm. Didn't get any alarms on pressure and the temps all held steady after the engine fully warmed up.

The sensor I installed was one that was measuring the oil pressure that I pulled last year thinking it might be faulty too. I might buy a brand new sensor and see if the readings change.

So this issue started occurring after you made a change? IF that is the case, that should have been mentioned in Post #1.

[kt_maxum]

Sorry for the confusion - No, to clarify the guardian issue and low block pressure fault happened before I swapped the pressure sensor. I changed the sensor to see if the fault was simply a bad sensor. Now that I've swapped the sensor, I'm getting more normal psi readings, so my hope is the issue was just a bad sensor and not a blockage.

My last post was just saying that the "new" sensor I installed was an old spare I had from a couple years ago that may be worth upgrading to a truly brand new one.

Thanks!
Ken