Hi John
I have reservations with the "soot" issue in your exhaust. Besides other
things I am a certified diesel mechanic and in all my years of marine and
industrial work have never run across this issue. There are 4 main reasons
your engine will smoke black.
1: Lack of air, either a plugged air filter or collapsed hose can cause
this, but the volvo factory setup it is impossible.
2: Too much fuel from the injection pump to the engine, but this will result
in an overpowered engine and since you describe a power loss again I will
rule this out.
3: Worn injector tip/tips or sticking injector/injectors. This one is also
easily diagnosed. With the engine idling at the dock listen to the exhaust.
If the usual putt putt putt is irregular normally thats an injector. I go a
step further, I tie off well to the dock. I work my engine in gear at full
pull and then I use a wrench and loosen the injector line to the injector,
the engine will fall in power and I listen to see if the remaining injector
has the engine runing smoothly, then I tighten the first injector and open
the second. The engine should fall to the same rpm and sound the same. If
ANY difference is noted pull both injectors and have them rebuilt. Dont go
to a boat place, take them to the nearest place that works on Semi trucks,
you'll find the Volvo nozzle quite common. A personal "tip" or cheat of mine
with the volvo injectors and other that are "clamped down" in place instead
of threaded in. Loosen the 2 nuts that hold the injectors in about 2 turns,
enough the brackets that hold them in place will move slightly then start
the engine, they will pop themselves out, failing this losten them another
turn, lightly tap them with a hammer and start it again, if they still stick
work the engine until 1 pops out. Lightly tighten it slightly snug and
repeat until the other pops out and then pull them both. They can be a bear
to remove otherwise and even I have ruined injectors trying to pry/twist
them out. I have pulled over 100 this way with no problem.
4: Late injection pump timing, this one is also easy to look for. The engine
is hard starting especially cold, when it starts it smokes white/grey and
until warm and sometimes even a little when warm. (next time it's at idle
after dark shine a good flashlight behind the boat, if you see smoke in the
beam bingo) Under light loading it runs smoothly but as soon as you ask for
"all she's got" she smokes black like a destroyer. Put her in gear and throw
her the coal while tied to the dock. look at the exhaust, is it making wet
black soot right on the water behind the boat like black lilly pads? If so
the timing is late.
I have yet to work on a 6A or 6B that the timing was even close to correct.
Without getting all technical the system used to drive the pump with even
moderate normal wear can have the pumps as late as 5 degrees or more easily.
In order for soot to build up in the manifold enough to restrict, your
exhaust would have to almost be liquid and SOAKED in oil and unburned
diesel, and then have to cool and harden layer by layer. Long before the
manifold built up enough to choke up your much smaller exhaust port in the
stern would have been completely plugged as the exhaust was cooler there
creating more buildup than the hotter manifold. You wont find a diesel even
2 hours old without a layer of soot in it, but as it builds up it gets blown
away in chips and chunks every time you throttle up.
Also LONG before it affected power or performance of your motor so much
back pressure would build your exhaust would be a loud hisslike a punctured
tire or blown air line whenever you wound her out, If you just hear putt
putt putt your fine.
These symptoms affect ALL diesels not just our volvo's and these tests also
work on any marine diesel.. If you are even slightly handy with tools you
can test the injectors in less than 5 minutes. If they test well I can
easily tell you or your mechanic how to manually bump up your timing just
for a test. My bet is slow timing and the volvo is very forgiving about
timing. If the increase works do it again until you hear a distinct diesel
"knock" when she's working, at that point back it off a bit and your all
done, no rocket science involved. Keep in mind that by design the 6A and 6B
will smoke slightly black at full throttle when worked hard enough to pull
her below her max rpm. If it smokes before it starts working hard and
pulling down it's injectors or pump timing. Although it could be a problem
with the pump I consider our pumps to be the most bulletproof in the
business, built well and simple design with little to go wrong. I have seen
one bad one, and that guy ran it for years with no fuel filter and then his
wife ran gasoline through it sealing it's fate.
Anyway I hope this helps you. If you narrow it down I'll be glad to tell you
how to fix it .
Claude
