Severe Power Loss after warmed up

[BPIDAN]

370 DB with Cat engines. 300 hp each. Last season the engines were blowing severe black smoke once warmed up. At first engines ran perfect. Once brought back down to low speeds the engines would not accelerate and produce rpms in gear. In idle rpms would climb just fine. We decided the fuel was old and drained over the winter. Put in fresh diesel just before launching this season.

Again, we have the same problem. It even seems worse. No power and cannot get the rpms up over 1800 rpms when warm. I have not replaced the fuel filters or water separator filters yet. I do have the filters for the Raycor separators and wanted to wait until I knew the old fuel was gone. I will do that today but in the meantime if anyone has any other suggestions, I would appreciate it.

This boat is not mine. I am helping the widow of the owner who died last season so I am diesel challenged. My boat, a Carver 380 is gas.

Thanking you in advance.

 

[BPIDAN]

UPDATE

New filters did not work. If anything it is worse. Won't go over 1800 RPMS without bellowing black smoke. Lower RPMS are ok.

 

[alnav]

BP, the most likely causes of black smoke are airflow obstructions, engine overload or defective injection. You might be able to do something about the first two and it might be one of them since it sounds like both engines are acting the same. If there are air filters, you should check them and clean or replace and make sure the intakes are clear. Could the hull be heavily fouled? I'm doubting it is since I assume you are in fresh water but that could cause black smoke due to overloaded engines.
If it's injection-related (which is usually the most likely) I believe you will need to consult with a diesel mechanic. If you can find the engine label plates, it might help to post the exact model number of the engine (probably 3116?). Also, is the boat a Sundancer or Sedan Bridge? There are folks with much more knowledge on this than I; hopefully you will get more and better advice but give it a couple of days, this board is somewhat quiet on summer weekends.

 

[BPIDAN]

Thank you for the response. To answer your questions, yes this is a freshwater boat and the hull is very clean. The engines are 3116's and the boat is a Sedan Bridge. We are located in Colorado. I do not know if the altitude was ever an issue with this boat as this is the first time I am working on it. It may be the boat always had this problem since 2006 when it was launched here. The owner had the boat shipped here from Florida. What is strange now is that I did get the boat to maximum rpms and planed out a couple of times before. Yesterday after I changed the filters in the Water separators, I could not get past 1800 without blowing black smoke. The filters were very black and completely clogged. I did rinse the housings once with fresh diesel. Popular opininon on the dock is the injectors. Since everyone else is gas we are all diesel challenged.

 

[timjet]

Since your issue with low power and black smoke is occurring in both engines and there is only one thing both engines share I would first eliminate fuel as a possible cause.
I know you refueled and changed the filter but what do the fuel tanks look like.
First and easiest is to check the vacuum gauge on the racors. When at 1800 rpm are you showing any more than 4-5" of vacuum. If so you have clogged filters and must eliminate the clogging issue. If you have no vacuum gauge, purchase a cheap one and install on the out put side of the racor.
It's very possible you have more than one issue to deal with. First make sure you do not have a fuel restriction issue. After that to deal with the black smoke issue go to boatdiesel.com and work out that issue with them.
Good luck.

 

[BPIDAN]

Thank you, I think you are right and will find out the vacuum rate. I am also going to check the new filters I installed and see if they are plugged up again. If the tanks are the issue, will multiple filter changes start to make things cleaner or do I need to somehow clean the tanks?

 

[timjet]

If the tanks are the issue, will multiple filter changes start to make things cleaner or do I need to somehow clean the tanks?

Multiple filter changes probably will only lighten your wallet. Look inside the tanks and see if debris is evident. If so you will probably need to hire someone to clean the tanks. Fuel polishing will only clean the fuel not remove the debris on the bottom.

But before going to this effort make sure you are attacking the right problem. The vacuum gauge will indicate if fuel is restricted going to the engine. If so you must fix that issue first before attempting to fix the smoke issue. Restricted fuel is not the cause of the black smoke, however it's certainly possible what ever is causing the black smoke is preventing the engine from reaching it's proper rpm. It's just far easier to determine if you have a fuel restriction issue than digging right in and trying to fix the smoke issue. I'm guessing but I think you have two issues going on that are not related.

Good luck and let us know what you find.