Yamaha F350 2013 Excessive Exhaust and black smoke puff on startup

[RvParagon]

I detailed problems I was having with the port motor on my vessel in a thread titled:

2013 350HP Yamaha Fuel Slick when run and when flushed

After weeks in the yard and $$$$, I resolved the problem. When I returned the boat to the water the starboard engine was "acting up". It seems to run perfectly fine, but bubbles excessively out the exhaust below water at idle and also spews a lot more exhaust out of the exhaust port above water. I know there can be variation in the exhaust out of the hub, but this is extreme bubbling at idle. The port engine, as it should, has zero bubbles out of the hub at idle. I also have confirmed with multiple other Yamahas that they don't bubble at idle. I have read many threads on this topic and many people try to make the argument that it is normal, but I know for sure that it is not- also because of this:

The other clue is that it started puffing black smoke at startup- then appears to run clean although I suspect it is running rich as I can smell it. Once when I was idling for an hour, turned off the motor and then started it- it blew a load of carbon onto the water. This has never happened in the 7 years running these motors.

During our time in the boatyard, the mechanic used the starboard Motor as reference when replacing the port powerhead. He had to pull things apart to look at it, so I am suspecting that something was tweaked or left unconnected since the motor was running great when it went into the shop and had this problem coming out.

Anyway, wondering if the great people of this forum might have some ideas?

I will probably inspect the coils, plugs and injectors next. Also trying to get them to send a tech down with the YDS software.

Thanks.

 

[RvParagon]

I think I am just talking to myself, but I'll continue writing. I had a technician come down and run the diagnostic software. No codes. We sequentially dropped each cylinder and performance was identical for all. All injectors passed the YDS test.

After running the motor at 1100 RPM for about 30 minutes while towing an asset, I stopped the motor and when I restarted, a ton of black soot came out- see photo.

The motor runs fine otherwise although I have noticed that on startup it has started sounding more subdued than the other motor (not revving as high).

I am about to go pull the plugs to visually inspect... any thoughts anyone?

 

[dwco5051]

I know nothing about your motor but if I had one of my diesels trucks acting like that I would say either it is burning soft coal for fuel or it is a bad injector.

 

[dingbat]

I think I am just talking to myself, but I'll continue writing. I had a technician come down and run the diagnostic software. No codes. We sequentially dropped each cylinder and performance was identical for all. All injectors passed the YDS test.

After running the motor at 1100 RPM for about 30 minutes while towing an asset, I stopped the motor and when I restarted, a ton of black soot came out- see photo.

The motor runs fine otherwise although I have noticed that on startup it has started sounding more subdued than the other motor (not revving as high).

I am about to go pull the plugs to visually inspect... any thoughts anyone?

From another site

Yamaha service manager said bubbles were from motor skipping from coil issue lats year, this year the coil had become so dislodged that it was tossing HF electricity all over the place and messed up the possessor causing the multiple cylinders to not fire correctly.

 

[RvParagon]

Thanks for the replies. Interesting about the HF interference from the coil. In my case I don't think that is the issue because we ran a test to individually drop each cylinder and all cylinders changed the performance in the same way. Also, I pulled all of the plugs since the last post and they are all covered in carbon- indicating to me that something is affecting the mixture equally in all cylinders. Later today I'll be doing some exploration, my gut feeling is that the mechanic left a ground wire off and its tweaking a sensor or even the ECU itself. He replaced the powerhead on the other motor and its missing numerous bolts and nuts and even this motor is missing some bolts from when he took the intake manifold off. Unfortunately he is not the most organized so definitely a good chance other bolts and connectors are missing.

 

[Faztbullet]

Is VST leaking???

 

[RvParagon]

For the sake of completion: I finally resolved this issue. I swapped the VST and low pressure fuel pump between motors. I expected to see the problem follow the VST and pump but instead both motors started working again. This indicated that the VST and pumps were both fine but not initially installed properly. Perhaps the vapor hoses were swapped, not installed or just loose. Unfortunately I don't have a perfect explanation, but it clearly had to do with improper VST hose installation. So if anyone out there has belching carbon after idling and excessive exhaust production (rich smelling too) check the hoses to your VST.

R/V Paragon Out and switching back to channel 16

 

[RvParagon]

Is VST leaking???

Just saw your post. You were close. I saw no evidence of the VST leaking, but see my other post....you are spot on that it was VST related. Thanks.