2004 5.0 OSI-EF not going over 3000 RPM

[serpico1]

I have a 2004 Rinker 312, with twin 5.0L OSI-EF engines and ocean series duo prop drives with SS props.
I took the boat out for my usual start of the season test drive.
The boat, while at the dock, ran perfect. while in neutral, I was able to rev the engines all the way up to 5000 rpm.
But, then I took it out to open water. travelling through the channels at low speed, around 2000 - 2500 rpm. all seemed fine. But then when I went to WOT, the engines would not go above 3000 rpm, like there was a governor limiting its speed. There was no hesitation, no backfiring, no misfiring, or sputtering. it just topped out at 3000 rpm. Although, I do feel a sight vibration in the boat once it gets up past 2000 rpm while in gear. no vibrations when its in neutral.

So far, I have replaced the distributor caps, rotors, plugs, and fuel/water separators. The fuel from the filters appeared to be fine, there was no water or particles floating in the fuel and it smelled fresh, as if it just came fuel station. I tested both fuel pumps both at the dock and under load at 3000 rpm. and the high pressure reading at the fuel rails was within spec, at 54 psi in the starboard pump and 56 psi in the port pump. the reading was steady and the same at the dock and under load.

I have been seeing others with similar issues posted, with suggestions about bad sensors and the engines being in "Limp Mode". the engines do not appear to be overheating or have low oil pressure. Although, the gauges for the port engine have not been working for a couple years. But the gauges for the starboard engine are reading within normal ranges. Oil level in both engines is good, with fresh oil and new filters done in April 2023. I have no audible alarms going off.

Any suggestions? possible sensors to check/replace?

 

[dubs283]

I would verify idle timing and full advance

 

[serpico1]

I will check it out. Although, I believe timing and advance is all controlled by the ECM. also, these are twin engines. both engines having same issue. so, what would the odds be of both engines having a timing and advance issue?

 

[muc]

I will check it out. Although, I believe timing and advance is all controlled by the ECM. also, these are twin engines. both engines having same issue. so, what would the odds be of both engines having a timing and advance issue?

Probably not. Do you have two gas tanks or just one?

Some twin engine setups will set Engine Protection Mode in both engines if one goes into it, if your boat has the master/slave cable installed.
But you will usually get a warning horn if Engine Protection Mode is engaged. Do you get the 2 beeps at key on?

 

[serpico1]

I have dual tanks. I have a few ball valves that were installed in the fuel lines by the mfg. So I am able to have the engines draw from separate tanks, both tanks, or 1 tank.

I am leaning towards the engines are in Engine RPM reduction mode. Possibly due to a bad sensor.
But, as I said both engines seemed to be limited to 3000 rpm. I can imagine a sensor in each engine going bad at the same time. Unless, the engines are somehow tied together, so once one engine goes into rpm reduction mode from faulty sensor, both engines go into the mode.

Although, i have not gotten any audible alarms and the alarm horn does work, as it sounds when I turn the key to on for each engine and then goes silent when the engines start.

The one thing that has mean leaning to possible the port engine going into rpm reduction mode, is the dash gauge for that engine (a Faria multigauge) has the temperature and oil pressure at zero, so it appears the gauge is not working or the sensors have gone bad. But, I believe the gauge has been out since last season, before this issue started.

 

[JTown12345]

Did you replace your impeller this year? VOLVO has a good manual on how to make sure the cooling system is in tact. Cooling is one reason for SLOW mode.

 

[serpico1]

No, I have not replaced the water pumps impellers. The boat gives no indication of overheating unless the temp sensors are bad.
This is a twin engine boat. Would one bad impeller, put both engines into slow mode?

 

[JTown12345]

No, I have not replaced the water pumps impellers. The boat gives no indication of overheating unless the temp sensors are bad.
This is a twin engine boat. Would one bad impeller, put both engines into slow mode?

I have 2 Penta 5.0fi. Oddly enough when I went into slow mode last night, the other one wouldn’t get above 3000 rpm’s, or it struggled to run at full capacity it seemed.

I read through your checklist and didn’t see the impeller. I know they’re supposed to be changed every year. Just wondered.

 

[muc]

your engines each have two sensors for temp and oil pressure. one for the gauge and one for the computer. slow is controlled by the computer.
might need to scan the engine

 

[serpico1]

I have 2 Penta 5.0fi. Oddly enough when I went into slow mode last night, the other one wouldn’t get above 3000 rpm’s, or it struggled to run at full capacity it seemed.

I read through your checklist and didn’t see the impeller. I know they’re supposed to be changed every year. Just wondered.

Ok, thanks.
But if an impeller was broken or not pushing enough water through the pump. Then the engine would start to run over temperature and overheat. Which should trip the High temp alarm and sound a beeping alarm sound. Which it doesnt do. But, perhaps the impeller and temp sensor both went bad. I will take a look, its only a few screws and easily accessible.

Although, I have to say. I have never replaced the water pump impellers every year. I usually check them every two years and keeps a spare on board should one fail while out on the water. As for actually replacing them. Its probably been about 5 years since one actually had to be replaced.

 

[JTown12345]

No, I have not replaced the water pumps impellers. The boat gives no indication of overheating unless the temp sensors are bad.
This is a twin engine boat. Would one bad impeller, put both engines into slow mode?

I have 2 Penta 5.0fi. Oddly enough when I went into slow mode last night, the other one wouldn’t get above 3000 rpm’s, or it struggled to run at full capacity it seemed.

I read through your checklist and didn’t see the impeller. I know they’re supposed to be changed every year. Just

Ok, thanks.
But if an impeller was broken or not pushing enough water through the pump. Then the engine would start to run over temperature and overheat. Which should trip the High temp alarm and sound a beeping alarm sound. Which it doesnt do. But, perhaps the impeller and temp sensor both went bad. I will take a look, its only a few screws and easily accessible.

Although, I have to say. I have never replaced the water pump impellers every year. I usually check them every two years and keeps a spare on board should one fail while out on the water. As for actually replacing them. Its probably been about 5 years since one actually had to be replaced.

I didn't replace one for 2 years once (Novice boater myself) and when I took it out, the fins were warped on one part of the impeller where they looked like shark fins. Who knows how long it sat in there with the previous owner because I'm in Michigan and we don't use our boats for 6 months haha!