My MC5c with a 6V71, up-sized injectors, Jake brake and Alison automatic began misbehaving recently. When the wife and I set out for a few days exploring over hill and dale the rig blew an embarrassing amount of black smoke if asked to climb even the gentlest grade or to accelerate even modestly and it had noticeably less power than I had remembered. When last driven any significant distance a few months ago we had neither of these problems. Since arriving home I have coincidently removed the lower housings from each of my three air cleaners and have found something peculiar (which may or may not be related); there was a large collection of water in the bottom of one while the other two were bone dry.
A diesel mechanic I found in the yellow pages (on Labor Day) declared the 6V71 a very simple beast and stated that he could think of no reason for such a precipitous change (after offering, “sounds like it’s just getting old).
How important is it to seek out a “bus mechanic” for engine work when you can instead of a “diesel mechanic” -- or even a “marine diesel mechanic” when in an isolated coastal community? I am within 100 miles of Southern Oregon Diesel but the passes between the Rogue River Valley and the Umpqua Valley seem daunting with such a misbehaving engine.
Just to stick my pair of pennies worth in here, it sounds as if you've lost an injector tip, or you hav an injector that has frozen.
Pull the rocker cover and manually pull the rack to the full open position, checking to see if any of the injectors are hanging. I would also check to see if there is a broken injector actuator somewhere along the line.
If that isn't the problem, check to make sure you have air going through the engine... remove the air cleaner to blower tube and see if the smoke clears up. If it does, I'd look for a plugged intake, not just a single air cleaner that is plugged. It's amazing how the squirrels and rats can make homes in the weirdest places.
If none of the above finds the problem, you may need to pull the injectors one by one. It is very possible you have lost a tip from an injector, which is just throwing raw fuel into the cylinder. A possibly asy way to find the problem is to loosen the exhaust manifolds and find which port is wet. If you find one, thast is a bad injector or operating parts.
If you have more than one it could be the same thing.
If all of the ports are wet, Check the intake again and start looking for other reasons.