Cat 3116 sync problem.

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M

Mont-Blanc

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Joined
May 15, 2022
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I am crossing lake Ontario and my boat sync started to randomly go toward rhe port side but the rpm's don't change. The sound does !

Any ideas ?
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Can you disengage the synchronization and adjust RPM by ear?
 
Are you gas or diesel? Sorry, forgot this is a Cat boat.

One way of diagnosing this would be to get a photo tack from Amazon. This would allow you to determine if your tachometers are reading accurately.

The odd part here is that you feel the sound changed but the RPM did not. I am at a loss as to why the RPMs would change on their own. Now if you are a gas engine you could be suffering from misfires, only I would think that would show up with an RPM flutter. Not relevant to diesel engines.

Do you actually have an engine synchronizer or is just a gauge to help you manually sync them?

If there is an actual engine synchronizer than we should be looking at that. With synchronizers, if the unit has an issue reading the slave engine it usually responds by speeding up the slave engine. However, this too usually shows up in the tachometer.
 
It sounds to me like a worn drive pin on the port engine. Very easy to replace.
 
In the OP's video, the variation in RPMs in the starboard engine is visible and audible. Did the operator touch the throttle during this episode?

In addition to that question, more info is needed here. Which engine is the "master," and which the "slave"? What kind of synch device is installed? Is it part of an electronic control system, such as MMCs? If the latter, a voltage hiccup could explain almost anything.
 
tiltrider1 said:
Are you gas or diesel? Sorry, forgot this is a Cat boat.

One way of diagnosing this would be to get a photo tack from Amazon. This would allow you to determine if your tachometers are reading accurately.

The odd part here is that you feel the sound changed but the RPM did not. I am at a loss as to why the RPMs would change on their own. Now if you are a gas engine you could be suffering from misfires, only I would think that would show up with an RPM flutter. Not relevant to diesel engines.

Do you actually have an engine synchronizer or is just a gauge to help you manually sync them?

If there is an actual engine synchronizer than we should be looking at that. With synchronizers, if the unit has an issue reading the slave engine it usually responds by speeding up the slave engine. However, this too usually shows up in the tachometer.
Click to expand...
It is a diesel boat.
It is just a gauge to help you manually sync them.
It is not a sync module that allows me to drive eith only one stick, it just help me make shure the boats engines are working at the same strength. The boat is 2002.
 
hmason said:
It sounds to me like a worn drive pin on the port engine. Very easy to replace.
Click to expand...
Thank you for that suggestion, I will inspect today. But yesterday it took an hour before it starts doing it, a worn drive pin would do that constantly ?
 
hmason said:
It sounds to me like a worn drive pin on the port engine. Very easy to replace.
Click to expand...
Thank you for that suggestion, I will inspect today. But yesterday it took an hour before it starts doing it, a worn drive pin would do that constantly !
Blissboat said:
In the OP's video, the variation in RPMs in the starboard engine is visible and audible. Did the operator touch the throttle during this episode?

In addition to that question, more info is needed here. Which engine is the "master," and which the "slave"? What kind of synch device is installed? Is it part of an electronic control system, such as MMCs? If the latter, a voltage hiccup could explain almost anything.
Click to expand...
I did not youch the throttle, that is the problem, it does it by itself. There is no master slave sync here, it is just a gauge to help me manually sync them.
No electronic control here, the boats year is 2002.
Here is a new video where I opened the hatch so you can ear the sound better.
 
Ok you have no syntonizer. The needle is a gauge to tell you where to apply more throttle to sync up.
It is doing this on its own. Your rpm on starboard is dropping by itself.

Varying rpm on an engine always start with fuel and filters. I would bet if you did a full power test you will have problems with the starboard engine rpm.

Change filters on both sides. And report back.
 
The first video made me agree with Greg QS that it was a fuel filter issue. The second video suggest that you have a tach pickup connection issue. I would inspect both.
 
Although changing the fuel filters has been suggested, I don't think it will solve the issue as at <1500 RPM the engine is flowing likely about half of it's full throttle fuel.
It does also not explain how this condition didn't happen for the first hour.

I'm perplexed as to what the latest video shows.

Port engine at just over 1000 RPM and constant, all good.

Stbd. engine at just under 1500 RPM and falls 100+/- and then recovers.

When the engines were 450 RPM apart the Sync. Gauge was on center which means no RPM adjustment is required. Thats odd. Could this simply be because that 450 RPM difference is out of the sync. gauge's range? Your ear is assumed to be better than that to get close.

In the earlier 11 second video both engines were at about 1250 RPM and the Stbd. engine lost 100 RPM with the sync gauge acting as expected, pointing to Stbd. Both gauges recovered on their own in both videos.

You say the being a 2002 engine, "no electronic control here". My 3408 Cats were built in 1993 and have programmable electronic engine controls. Are you sure your throttles are not electronic?

Where is your Tach Signal generated? Magnet pickup, counting ring gear teeth or perhaps alternator pulses?
 
Keep it simple.
The most common problem for lack of power and rpm problems is lack of fuel . IE clogged fuel filters. It is the easiest to check and cheapest repair. You cannot further diagnose you problem if you don't know you have good fuel flow.
Fuel filters clog over time. They are doing there job but can shut you down. Once there plugged there plugged. This explains no problem the first hour. Change the filters and then lets see.
.
 
Several years ago I was traveling down Puget Sound with a friend and he said my port engine was dropping 100 rpm and then picking back up. We were at 1600 rpm and the engine synch was engaged. At our destination I replaced both the Racor fuel filters. The port one looked worse than the stbd. On our trip home the problem was gone. Check your filters.
 
Agree, check the fuel filter on the affected engine for clogging. When an engine starts dropping revs one of the first things to check is the filters. You may have gotten a load of dirty fuel or the dirt has built up over some time or a valve has been bumped while you were crawling around.

Check any valves ,that they are closed. Years ago I got caught from crawling around in my engine compartment. My engine after many hours of use started loping, almost quitting each time. We were towed to a place to tie up who had mechanics.
Next day I found out I had bumped slightly open a valve overhead. Never felt it but it sure affected the engine. Happened a couple more times over the years but i knew what it was.
Now that valve has had its handle shortened, a hole drilled in the remaining handle and a Tyrap secures the handle in place. No more trouble for the last 20+ years.

So check for anything like that and then secure it.
 
I just got them deluverd today. It's tomorrow's first job! Will keep you posted. Thank you!
 
Finally, the Racor filter I got was not compatible with my system.

I did change the fluid and filters of my transmission on the starboard engine. (Had only one spare filter)

I left Toronto this morning towards Port Hope. My boat was working perfectly from 8h30 to 12h45
Then it started again. :(

I'm checking for Parts trying to fix my problem.
Thanks to everyone who tried to help me.
 
It’s not clear to me as to if you changed the engine’s Racor fuel filter or not. Please clarify!

If not, the fact that you ran for 4 hours with no symptoms seems to indicate that the original filters are not plugged.

That does not mean that the cause is not a fuel delivery issue.

Are there fuel pressure gauges onboard (maybe in the ER) that you can monitor while underway to see if they move in sync with the tach?
 
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It was alright from 8h to 12h40, than started forcing again. So I stopped at Port Darlington and found a shop that had Racors, 1 x 30 microns and 1 x 10 microns. He called Napa and got me diesel filters delivered as well. When I removed the Racors, I understood that was the problem! We changed the Racors and the filters. So far so good almost 2 hours. On our way to Cobourg. Thank you for asking. Very thoughtful!
 

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Good on you. Let's hope that this resolves the issue..

You should really consider stocking on board in a sealed dry container at least one set of all fuel filters so that in the event that you get some dirty fuel and things go pear-shaped again, the fix is in hand.

I stock the Racors and the OEM Cat filters.
 
All good now. Thank you all for helping, I have been on boats for 20+ years doing maintenance on many boats. To know that someone with experience can read your posts and bring knowledge and solutions to fix your problems.

Few lessons learned ... make shure you have yous spare parts and equipment before you leave. (I usually do) and you can rely on the trawler forum community for peers support.

Will try to pass more time on this forum tu return the faver.

Enjoy your boats !
 

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