It could be bio-growth causing the black. Are you sure it's not dark green? I have experienced diesel getting contaminated in that manner and it's a nightmare to get rid of. It's some sort of algae. The sulfur used to keep it in check I've been told (true?) and now that we're low/zero-sulfur it's easier for the stuff to grow.

This link is directed at large trucks, but the info is similar. Multiple reasons for dark fuel:

http://www.diesel-fuels.com/bad-diesel-fuel.php

Who knew?

Yeah, that makes some good sense, the dark color must be the bug. So I'm thinking I'll drain the tank completely, wipe it all down with bleach or something once it's empty then dry it out thoroughly? Would something simple like a bleach wipe down be an effective biocide?

Use Kerosene to wipe it down. It will help break up the sludge.

Thanks bill, used kerosene to clean out the tank as best I could, definitely some sludge in the bottom. Replaced fuel filter and bled all lines to the injectors. With some persuasion I can get the engine to fire but I can't get the forward cylinder to fire consistently/evenly. The rear is steady and smooth but the forward is louder and more metallic sounding and will miss when the throttle is pushed and won't run at all at idle. Come to think about it, the engine has always had the loud tinny sound from I'm hearing from the front cylinder, I just assumed that's the way the engine sounded and you j30 guys were just gluttons for noise abuse but now that it's missing I can hear the rear cylinder firing on it's own and it's much smoother and quieter. Now I'm thinking injector? What's involved in replacing/tuning? Hope this thread helps someone else struggling with their engine.

The problem is probably related to one of two items.

1. Injector nozzle not spraying a mist (clogged injector)
2. High pressure fuel pump output sending wrong amount of fuel to cylinder.

#1 can be fixed by removing the injector and taking it to a diesel shop so they can pop test, and if required replace the nozzle. They can shim the injector to meter the right amount of fuel. Pull them both and label which cylinder they are matched to. When replacing the injector, be sure to replace the mica insulator that fits between the injector and the head.

If that doesn't fix it, next try

#2 requires returning the high pressure pump to a Yanmar repair facility. They can rebuild the seals and setup the fuel rack for proper metering of fuel at all rpms. This requires special test equipment and is why the task needs to be done at the Yanmar repair center.

Refer to section 3 of the 2QM15 Service Manual located on the J/30 page under the menu Info, Diesel Engine Maintenance. This has detailed diagrams and rebuild procedures for the injector and fuel pump.

problem solved. Pulled the injector and brought it to a fellow club members shop where we pop tested it. The nozzle itself wouldn't even re seat itself after the first test, just stayed open spraying a little stream of fuel. So with the nozzle replaced with a salvaged nozzle from another old yanmar engine we got a successful test 1900 psi. I put the injector back in today and the engine runs better and quieter than it ever has. I am having some trouble getting the fuel line screws to reseat at the injector, a little diesel seems to be dribbling out, can I use teflon or locktight to get the threads to seal?

Thanks for all your help!

josh

Josh,

Are these "banjo" type fittings with the copper washer gaskets like on my 2GM? If so, replace the copper washers.

I reread your post. The supply lines are threaded, the recirc lines are banjo fittings. Don't get any teflon tape in the flared section of the supply line, only on the threads. Ideally you should replace the leaking line as this is designed to seal with the flared fittings and is under extreme pressure.

The fuel lines seem to have seated themselves, no leakage this last trip. But it would seem the old engine has a new issue to be resolved, I'm thinking it's related. Engine starts smooth and settles into idle quickly but motoring back into the harbor I noticed some light grey/white smoke out of the exhaust. Then an engine alarm went off. I turned off the engine, sailed back to the mooring on the jib and engine started and ran normally when I started it on the mooring. What would the alarm indicate? Related to the smoke?

It could be just steam from the exhaust, and potentially low water flow out the exhaust flashing the water to steam. Check the exhaust elbow to make sure it is clear. Is your engine raw water or fresh water cooled? Check the thermostat and the raw water pump impeller for raw water cooled engine.