RPM issue

[no_rulz25]

Ok boys and girls, here’s a new one for ya. We were out Saturday and after running at cruising speed for about 30 min I got the dreaded “check engine” alarm and notification on the dash. I immediately throttled down and it went away. All the temps were ok so I sped back up to a little over 3k rpm and after a min got the alarm again. After some time figured out I would only get the alarm over 3k rpm and if I went below 3k it would immediately stop. Anyone ever had this happen?

[AsLan7]

Ok boys and girls, here’s a new one for ya. We were out Saturday and after running at cruising speed for about 30 min I got the dreaded “check engine” alarm and notification on the dash. I immediately throttled down and it went away. All the temps were ok so I sped back up to a little over 3k rpm and after a min got the alarm again. After some time figured out I would only get the alarm over 3k rpm and if I went below 3k it would immediately stop. Anyone ever had this happen?

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We had that nr25 but it was the overheat alarm due to the engine not receiving enough water inflow at higher rpm’s.

The alarm would come on around 180 degrees on the temp gauge during cruise.

In any event, my first thought is something blocking your outdrive water intake. Did you check that? Bag, weeds, sticks, or anything in those intakes? This has happened to us a few times and I just throttled back...turned the engine off...jumped in the water and cleared some weeds that had lodged themselves in that intake. Started back up and away we went with no issues.


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[akorcovelos]

Also a telltale sign of a failing water pump impeller or thermostat stuck closed.

[no_rulz25]

Ok boys and girls, here’s a new one for ya. We were out Saturday and after running at cruising speed for about 30 min I got the dreaded “check engine” alarm and notification on the dash. I immediately throttled down and it went away. All the temps were ok so I sped back up to a little over 3k rpm and after a min got the alarm again. After some time figured out I would only get the alarm over 3k rpm and if I went below 3k it would immediately stop. Anyone ever had this happen?

.
We had that nr25 but it was the overheat alarm due to the engine not receiving enough water inflow at higher rpm’s.

The alarm would come on around 180 degrees on the temp gauge during cruise.

In any event, my first thought is something blocking your outdrive water intake. Did you check that? Bag, weeds, sticks, or anything in those intakes? This has happened to us a few times and I just throttled back...turned the engine off...jumped in the water and cleared some weeds that had lodged themselves in that intake. Started back up and away we went with no issues.


.

I don’t think that is the issue, my coolant remained around 160 deg. No overheating there.

[AsLan7]

Ok boys and girls, here’s a new one for ya. We were out Saturday and after running at cruising speed for about 30 min I got the dreaded “check engine” alarm and notification on the dash. I immediately throttled down and it went away. All the temps were ok so I sped back up to a little over 3k rpm and after a min got the alarm again. After some time figured out I would only get the alarm over 3k rpm and if I went below 3k it would immediately stop. Anyone ever had this happen?

.
We had that nr25 but it was the overheat alarm due to the engine not receiving enough water inflow at higher rpm’s.

The alarm would come on around 180 degrees on the temp gauge during cruise.

In any event, my first thought is something blocking your outdrive water intake. Did you check that? Bag, weeds, sticks, or anything in those intakes? This has happened to us a few times and I just throttled back...turned the engine off...jumped in the water and cleared some weeds that had lodged themselves in that intake. Started back up and away we went with no issues.


.

I don’t think that is the issue, my coolant remained around 160 deg. No overheating there.

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Yes but the alarm will sound if ECU senses low raw water pump pressure.

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[cmattj]

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We had that nr25 but it was the overheat alarm due to the engine not receiving enough water inflow at higher rpm’s.

The alarm would come on around 180 degrees on the temp gauge during cruise.

In any event, my first thought is something blocking your outdrive water intake. Did you check that? Bag, weeds, sticks, or anything in those intakes? This has happened to us a few times and I just throttled back...turned the engine off...jumped in the water and cleared some weeds that had lodged themselves in that intake. Started back up and away we went with no issues.


.

I don’t think that is the issue, my coolant remained around 160 deg. No overheating there.

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Yes but the alarm will sound if ECU senses low raw water pump pressure.

.

I’m with these guys..
Without knowing what code is present it would be a good guess.

Your temperature gauge on the dash is looking at the block sensor. The alarm can be triggered off of the raw cooling or lack off cooling leaving in the exhaust.
Very small thresholds as to limiting overheating that may not have occurred yet.
Let’s revisit what they did last October? Maybe something still restricting or impeller going away.

[no_rulz25]

The impeller is good, just changed that out. Is there a way to troubleshoot the water pump or just need to take a chance and change it out?

[cmattj]

The impeller is good, just changed that out. Is there a way to troubleshoot the water pump or just need to take a chance and change it out?

With closed cooling the engine and exhaust run two separate systems. Exchanger.. coolers.. exhaust are the ones looking a the raw side and have sensors.
We need a code as it could be as simple as a exhaust sensor reading high or false due to there nature of corrosion in salt water.
Do you have anyone that can come by with a scanner? That’s where I’d start as the code will be there for many more ignition cycles.

[AsLan7]

The impeller is good, just changed that out. Is there a way to troubleshoot the water pump or just need to take a chance and change it out?

With closed cooling the engine and exhaust run two separate systems. Exchanger.. coolers.. exhaust are the ones looking a the raw side and have sensors.
We need a code as it could be as simple as a exhaust sensor reading high or false due to there nature of corrosion in salt water.
Do you have anyone that can come by with a scanner? That’s where I’d start as the code will be there for many more ignition cycles.

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Agreed. The ECU code will tell you the entire story.

Below is the Merc cooling diagram but it will be similar to the VP. Like Matt mentioned, two separate systems with closed cooling. An antifreeze "closed" system that uses a circulating water pump like your car (without the huge radiator of course) shown in red, green, and yellow...

and

...the raw water system shown in blue. This system is more likely the alarm culprit. When you throttle up, the raw water system demands more water flow to keep the engine cool by spinning the raw water pump (housing your impeller) faster --but something may be impeding that water flow. The water enters thru the outdrive inlets and exits thru the prop (or captain's call if installed). Could be a bad impeller? Intake Blockage? Oil cooler blockage? Air leak (which is what we had at the transom inlet hose)? I know it's a pain to get a scan but it is the best COA.

When you fire her up on land with muffs you will be able to sense water in-flow by observing the amount of outflow from your CC or prop/transom exit. Rev to 3,000 rpm and check if you have a fair amount of outflow. That may give you your first indication of a blockage somewhere.

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[no_rulz25]

Thanks for all the info fellas.

[no_rulz25]

A little update, the mechanic scanned the engine and it showed no fault codes. He did say that it did throw some computer code that indicates the engine is not talking right to the dash, whatever the hell that means. He has a call out to Cobalt/Volvo and see what the story is.

[Big Block Power]

Canbus line issues.

[akorcovelos]

Man, these now boats sure are having a lot of electrical issues.

[Big Block Power]

Man, these now boats sure are having a lot of electrical issues.

The more tech you add the more issues you will have. I'll tell you they don't use as good of connectors that car manufacturers use either.

[akorcovelos]

Big reason I like critical components to be analog on high end stuff. On the Mercedes everything isn’t active, buttons, knobs, easily found without taking your eyes off the road. Same with boats, even more so, classy analog any day of tons of digital electronics, which are proving to be an issue.