Engines will not reach RPM

[Champ3555]

Good morning all. I am desperate to find information on how to repair my 2001 570 Voyager. First let me say this a beautiful well maintained, updated boat with around 900 fresh water hours. The specifications are as follows;

Engines-Cummins QSM11 535s Serial # Port 35016246, Starboard 35015841
Transmissions- Twin Disk

My issues are:
1) Port transmission seems to have a vibration that throws the engine into limp mode and will not allow speed of more then 1400 rpm. Throttles are slow to respond on both sides and I have to move half way up to get response.
2) Starboard engine will not exceed 1800 rpm.
3) The transmissions do not shift into gear smoothly. Slight bump when moved into drive mode

Known and recent repairs and service calls:
1) The previous owner replaced the starboard transmission which may account for the vibration due to misalignment???
2) Both drive shafts, props, bearings and rudders have been replaced or repaired due to a cable wrapping around the starboard prop.
3) Local Cummins technicians were paid $1,500.00 to diagnose engines under sea trial to determine RPM issues. They were unable to get a connection to the ports during this service call. I never received a report, only a bill.
4) Local marina (who is a Carver dealer) maintenance crew is completely clueless and the above incident with Cummins has me suspicious of any repair crews.

Any and all responses and recommendations would be greatly appreciated!!!!

[Viper]

Welcome aboard.

I've never had a transmission issue or an engine/running gear misalignment throw an engine into limp mode but who knows under the right conditions. Are you sure it's going into limp mode, are you getting an alarm or an engine light coming on indicating a fault? The reduced rpm could be the result of something else and not the computer giving that command. The vibration could be the engines, a misalignment, a running gear issue, or even fouled props full of weeds. I have to assume/hope that the techs checked the basics such as air filters, fuel filters, condition of the fuel, boost pressures, etc. Why weren't they able to hook up to the engine? Can't understand not getting a report of the findings from a tech you've paid money to diagnose a problem for you. Even if they couldn't come to a conclusion, they can give you a report of what they've done and the results of their findings. Find another tech is my advise.

[km1125]

QR_BBPOST...
3) Local Cummins technicians were paid $1,500.00 to diagnose engines under sea trial to determine RPM issues. They were unable to get a connection to the ports during this service call. I never received a report, only a bill.
...

I wouldn't be paying the bill if they didn't actually do the diagnosis (connecting to the engines is a HUGE part of this kind of diagnosis!!!), nor provide a report of whatever they DID do and whatever they DID find.

They could come back out and finish the job first, if they were really indeed qualified to accept it in the first place.

[Carpediem]

@champ355, Have you contacted Tony @ https://www.sbmar.com/ yet? He and his guys are foremost experts on Cummins issues. Tony has lots of instructional videos and tips on just about every subject on Cummins service and trouble shooting. I suspect that you have some kind of an engine wiring harness issue throwing fault codes to the EDU. I had issues with my QSCs on my Searay and it ended up being a bad harness. Replaced it and my issues disappeared. I was skeptical since I could not find any issues by doing continuity and resistance tests. I even took the time to swap harnessses from one engine to the other and the problem followed the harness.
Good luck to you. This would be so frustrating to have a big problem like that on a new to you boat. Sounds like you got really bad service by your broker and surveyor if this boat passed a Sea Trial prior to closing.
Carpe Diem

[Georgeviking]

As stated above it is imperative to first plug into the engine to ask how you feeling today?
One question I often ask is was any work recently done to the vessel? You have a vibration on a vessel that had a fair amount of running gear done and perhaps more work was needed. While I would want to know all about the engine first and normally that’s the easiest just plug it in I would seek someone else to try and get a connection perhaps it’s not them but onboard computer. Without that the transmission
Coupler could be disconnected from the shaft to check alignment. If you purchased vessel without the vibration and it all of a sudden started running sluggish could all be in engine stressing importance of a computer to computer connection being highly important.

[Champ3555]

Thank you all for the responses. I am bringing another tech in to diagnose in a couple of weeks.. I did recently get a verbal confirmation that the Cummins tech thinks the ECM is bad which could account for the incorrect gage readings and maybe even throttle issues.