Caterpillar 3116 Port Engine Drop in RPM's

Girlfriend III

Girlfriend III

New Member
Mar 15, 2008
106
Skipjack Cove, MD.
Boat Info
1996 Sea Ray 42 Aft Cabin
Engines
Diesel 3116 Caterpillar
Yesterday while crusing home on the Sassafras river with the Engine Sync on my port engine dropped from 1900 rpm's to 1400rpm's. I dropped the starboard back to match it at 1400 and it shot back up to 1900 and then back down to 1400. All filters are clean and new, I did not disengage the sync and try it again yesterday? Sound like an engine problem or a Glen Denning Problem?

Any suggestions would be greatly appreciated before I have to call Ransome Cat in for another $2000 invoice...

thanks !
 
The clutch on the engine sync could be slipping. I have the PDF manual somewhere. It's easy to check and adjust. You can also download the PDF from their website.
 
I think you have an injector seat leaking on cylinder #5 or 6 on the port engine.

If an injector seat leaks, combustion gasses push past the injector and fill the fuel gallery with air, down stream of the cylinder that is leaking. That essentially shuts down the cylinders affected. When a seat leaks, it beings as an intermittent problem then gets worse until the engine won't even run. The remedy is fairly simple and isn't too expensive (~$800), but it does take a special reaming tool which means you need to call your Cat dealer. If you are using an independent mechanic ask first if he owns the correct tools to ream the injector seats on a Cat 3116. If he doesn't, you will end up buying the tool for him……..Cat dealers handle this all the time and every dealership has them. Also, have all 12 injector seats done on the engines (at least all 6 on the affected engine)while the mechanic is there.
 
Just curious, are you sensing performance differences with the change in rpms? I ask because mine will vary at times and it is a connection issue. I literally tap the affected tach to correct it. Just a thought to consider.
 
The tach is driven by a tooth counter on the flywheel, so it is independent of the synchronizer. The synchronizer will sync the engines, no matter what either tach reads. But, I would run the boat without the synchronizer engaged to replicate the problem and rule out a synchronizer problem.

If there is an injector seat leaking, there is a definite performance issue………..it reacts like you pulled a throttle from 1900 rpm to 1400 rpm.
 
Thank you all ! Frank, I am having Cat come out on your suggestion. I truly appreciate your knowledge! And yes, it does react like I am pulling down the throttle to 1400 RPM
 
The usual diagnostics for the blown out injector seat is to put a piece of clear tubing in the fuel return line…….the returned fuel will have bubbles in it if the injector seat is leaking.
 
I had something similar a few years ago and turned out the turbo was freezing up. The SS risers started to leak and drip into the turbo which would rust and when it heats up, would sieze. It was a intermittent problem too. Rebuilt the turbo and replaced the SS risers with bronze risers. If you still have the SS risers, you are running on borrowed time.

Good luck in your hunt.
 
Change the fuel filters and separators first cause its cheap to do, bad fuel does alot of bad things. I work on cat equipment and that is a huge issue all the time then go from there. Just a thought for you
 
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Took the boat out again this weekend witout the syncronizers, did the same exact thing. All filters were changed out end of last season, I have 2 Racors and one Cat filter per engine, they look fine(Racors). Making an appontment with Cat today. Does anyone know what position the knob on the fuel primer pump on the port engine needs to be in? I can't find anything in the manual, right now I have it all the way clockwise till it stops. I tried to move it all the way counter clockwise and it seemed to restrict the fuel to the port engine, thinking this might be the issue with the port engine drop in RPM?
 
I had an issue several years ago with the primer pump malfunctioning which took me a while to diagnose. Purchased a new one from Cat ( siliconed the knob as to not let it back out). Problem fixed and I never use these.
Good luck but always listen to FW.
 
Frank, you were right on ! The Cat mechanic spent the first day with the site glass and we switched it from the good Starboard engine to the bad Port engine. An extreme difference in the bubbles in the site glass from the Port engine. We took everything apart, labeled it and he got his greese and reamer tool and starting reaming the cups. We saw a carbon imprint on cup #6, and of course we had to raise the floor so he could get the tool in there. This took him all day on his 2nd. visit. Today(3rd visit) he is putting it all back together with new O rings, setting the fuel rail and testing it again with the site glass. If the bubbles are gone we expect to Sea Trial it tomorrow. I will follow up on the outcome. I can't wait to see this invoice from Caterpillar. Thanks again Frank and all others that made suggestions !
 
Well, after all the work on the port engine we took it out for a sea trial, and I pushed it up and the port engine declined back to 1400 RPMS. The Cat mechanic was baffled as he watched the pressure meter go up and down. After several times off getting to WOT and the port engine dropping we decided to head back to the Marina. As I was turning he stated lets try this again, I throttled up and with him in the engine room he messed with the knob on the fuel pump primer and the engine shot back up and maintained RPMS @ 2100. So I purchased a new primer pump for $231.00 and we are back in business. While the port engine was blowing a lot of air it could of probably waited but I made my annual contribution to Caterpillar and all is good. Thanks to all for your suggestions...Off to St. Michaels for a long weekend !
 
i had similar problem, i installed 2 vacume guages on my racors, this will tell u if its a fuel related problem, i had a fuel line sucking shut,
 
Well, now it is 2016 and I am faced with the same problem. The only difference this time is I have some white smoke coming from the Port engine. From reading, this means there is air somewhere in the lines,bad turbo, bad head gasket, fuel pump or a slew of other issues. I assume that since the cat mechanic replaced the "O"rings on the injectors I can eliminate that? I am going to hook an air pressure line and see what can see/hear with a bottle of soapy water. Any other suggestions would be welcome. BTW, all new filters and racors last weekend did not fix the problem. I even took the Racors apart and cleaned some sludge at bottom of bowls.
 
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