5.0l MPI Single Alarm at 2000 RPMs and higher

[jahausbach]

@Nord2903, I just found and read this entire thread. Were you able to find and fix the problem?

4.3L MPI 2007 Searay Sport 185. Single Alarm at 20 RPMs and higher

Good Evening All, Looking for a little help. I am getting a single beep alarm when I am at 20 RPMs in my fuel injected 4.3L 2007 mercruiser engine. Previously I was getting a rough idle and the alarm would also sound at idle, which it is not doing anymore. When the alarm sounds at 20 RPMS...

forums.iboats.com

I have a 2013 Sea Ray with 5.0l MPI Bravo III and Smart Craft gauge package and the exact same issue. 2000 RPM, low water pressure, guardian mode. I am in my 3rd summer of troubleshooting this with my local Mercury marina. We have replaced the water pressure sensor, sea water pump impeller, sea water pump housing, converted the sea water pickup to thru hull (thinking I had Bravo-itis), the re-circulating water pump, the thermostat, and the water distribution housing. I also had them perform a citric acid flush of the water system after finding quite a bit of oxidation debris while addressing a separate issue with an exhaust flapper valve. Regional Mercury rep has been useless.

 

[dubs283]

Only thing I can think of you haven't listed is a blockage somewhere in the cooling system

Is the boat operated in salt water. Closed cooling or raw water?

 

[jahausbach]

Only thing I can think of you haven't listed is a blockage somewhere in the cooling system

Is the boat operated in salt water. Closed cooling or raw water?

5 years of salt water, then freshwater ever since. That was why we went down the path of abandoning the drive water pickup early on in the troubleshooting. With everything that has been replaced and done, I have good water pressure at low idle to about 3000 RPM (develops about 5 psi at this point). Above 3000 RPM, pressure drops off to below 1 psi causing guardian mode to activate. Once RPM drops down again, pressure picks back up.

 

[dubs283]

Are the exhaust manifolds and risers/elbows original?

 

[Fun Times]

What does the engine temperature do when the pressure goes low?

Any recorded overheat fault code?.

Even though you went to thru hull water pick up, was the inlet hose at the pump reused? / that ran to the transom… What color is the inlet hose (now?) (red or black)

Does the hose have a quick disconnect fitting in the middle? Maybe a bad seal/ or O-ring going on in there… or the hose is intentionally compromised or sucking closed at higher RPM.

If at all possible, Try carefully feeling the back side of the impeller housing at RPM and low pressure to see if the the housing seems to be getting extra hot.

Engine serial number handy?

 

[alldodge]

Something is just not right about the motors wiring
Disconnecting the "in-gear" switch (previous thread) kills the motor which should not happen.

BTW, the OP can reopen the previous thread

 

[QBhoy]

Hi. Just so I am clear. Does it have a registered fault of low water pressure or likely more odds on to be sw pressure, if so ?
Or is there no fault and you think it’s only giving 2000ish rpm and gaurdian?
If it’s the latter…can I be cheeky enough to ask if you are seeing only 2000-2500 rpm when revving her in neutral ? That being the case, I’d be all but certain that mpi engines after a certain age in the late 2000’s…won’t allow you to rev past about 2000-2500 rpm, when in neutral.

 

[jahausbach]

Are the exhaust manifolds and risers/elbows original?

yes, they are original. I have taken the outlets off and the internals look good from the back. It was at that point that I found a lot of corrosion debris and opted to perform the citric acid flush.

 

[jahausbach]

What does the engine temperature do when the pressure goes low?

Any recorded overheat fault code?.

Even though you went to thru hull water pick up, was the inlet hose at the pump reused? / that ran to the transom… What color is the inlet hose (now?) (red or black)

Does the hose have a quick disconnect fitting in the middle? Maybe a bad seal/ or O-ring going on in there… or the hose is intentionally compromised or sucking closed at higher RPM.

If at all possible, Try carefully feeling the back side of the impeller housing at RPM and low pressure to see if the the housing seems to be getting extra hot.

Engine serial number handy?

Engine temperature never rises, and no overheat codes.

Inlet water hose was not reused. Original hose was black. New hose is a black nylon reinforced hose.

The original hose did have a quick disconnect fitting in the middle. I have the same theory about the inlet hose collapsing. I have a new non-collapsible hose that I haven't tried yet.

Engine serial number 2A039039

 

[jahausbach]

Hi. Just so I am clear. Does it have a registered fault of low water pressure or likely more odds on to be sw pressure, if so ?
Or is there no fault and you think it’s only giving 2000ish rpm and gaurdian?
If it’s the latter…can I be cheeky enough to ask if you are seeing only 2000-2500 rpm when revving her in neutral ? That being the case, I’d be all but certain that mpi engines after a certain age in the late 2000’s…won’t allow you to rev past about 2000-2500 rpm, when in neutral.

It is definitely low water pressure. The Smart Craft gauge shows the pressure drop just before alarming and displaying the code for low water pressure. Additionally, my marina hooked the laptop up to it and confirmed the ECU is seeing the low water pressure to. I think I forgot to mention in my original post that Mercury loaned an ECU last year and the fault did not go away.

This is happening with the boat in gear.

 

[jahausbach]

Something is just not right about the motors wiring
Disconnecting the "in-gear" switch (previous thread) kills the motor which should not happen.

BTW, the OP can reopen the previous thread

I have owned the boat since new. The only wiring mod I did was to pull power for the Lowrance that I added.

How do I start the process of reopening the thread?

 

[QBhoy]

It is definitely low water pressure. The Smart Craft gauge shows the pressure drop just before alarming and displaying the code for low water pressure. Additionally, my marina hooked the laptop up to it and confirmed the ECU is seeing the low water pressure to. I think I forgot to mention in my original post that Mercury loaned an ECU last year and the fault did not go away.

This is happening with the boat in gear.

Ok. Strange thing is though. At idle on a trailer, the actual water pressure shown on smartcraft is literally next to nothing, I know for sure. But it won’t alarm. You think the ecu was from an older version without the function perhaps ? Or is it just a faulty SW pressure sensor ? Is it unplugged at all ? Have you checked the wiring where it meets the harness and accessories plugs ?

 

[Fun Times]

Standard cooling system on yours? Not closed cooling…

Just wondering if anyone has tried thoroughly inspecting the thermostat poppet valve and exhaust check valves as maybe they are having an odd affect on the pressure at higher RPM.

Item 11 and 15,

Thermostat and Housing, Standard Cooling

Thermostat and Housing, Standard Cooling

www.mercruiserparts.com

Item number 19,

Exhaust Manifold and Elbow

Exhaust Manifold and Elbow

www.mercruiserparts.com

350 MAG MPI ALPHA/BRAVO EC - 1A300000 THRU 1A611927 and MORE

350 MAG MPI ALPHA/BRAVO EC - 1A300000 THRU 1A611927 and MORE

www.mercruiserparts.com

 

[jahausbach]

Standard cooling system on yours? Not closed cooling…

Just wondering if anyone has tried thoroughly inspecting the thermostat poppet valve and exhaust check valves as maybe they are having an odd affect on the pressure at higher RPM.

Item 11 and 15,

Thermostat and Housing, Standard Cooling

Thermostat and Housing, Standard Cooling

www.mercruiserparts.com

Item number 19,

Exhaust Manifold and Elbow

Exhaust Manifold and Elbow

www.mercruiserparts.com

350 MAG MPI ALPHA/BRAVO EC - 1A300000 THRU 1A611927 and MORE

350 MAG MPI ALPHA/BRAVO EC - 1A300000 THRU 1A611927 and MORE

www.mercruiserparts.com

Standard cooling.

Thermostat was replaced, and I assume the mechanic checked the housing while he had it open.

Exhaust check valves have both been replaced. One of them was sticking causing a high temperature on the riser. This has been corrected.

 

[jahausbach]

Ok. Strange thing is though. At idle on a trailer, the actual water pressure shown on smartcraft is literally next to nothing, I know for sure. But it won’t alarm. You think the ecu was from an older version without the function perhaps ? Or is it just a faulty SW pressure sensor ? Is it unplugged at all ? Have you checked the wiring where it meets the harness and accessories plugs ?

The mechanic checked the wiring and replaced the sensor first thing. I was told that the ECU was the same build as mine.

SmartCraft water pressure builds normally while in gear from about 1psi at idle to about 4psi around 2000 RPM from what I remember. I have not run it this year yet.