Northern Lights Genset

[Msamsen]

I have a M673D Northern Lights 5kw diesel generator (Luggar) that stopped running due to air in the fuel system and am at a loss for what to try next. Ive changed both filters, the lift pump, verified the shutoff valve is opening and the glow plugs are energized, bled the system all the way to the injector lines as per the manual and called the tech dept several times. Still no smoke and no fire.

Any advise would be much appreciated!

[twistedtree]

It sounds like you have done all the right things, but since it's still not working, something was missed along the way. So let's go back over things and take a fresh look.


You say is initially died because of air in the fuel system. How did you arrive at that diagnosis?

[Msamsen]

One morning while anchored, I tried unsuccessfully to start the Genset for the morining charge. When we eventually got under way, both main engines died about 5 minutes after departure. After bleeding both Detroit 453s, everything works normally for them. However, this did not work for the genset.

[Msamsen]

As for the air, I think it enters the main fuel distribution manifold through the tank supply lines that bleed back into the tanks when engines arent sucking it up. I have subsequently installed a low pressure priming system for easy bleeding after filter changes, etc.

[twistedtree]

OK, so it's possible the generator wouldn't start because of whatever stopped the mains, but it also could be something else. So let's just keep that in mind.


You said you bled the gen fuel system up to the injector lines, so where the injector lines connect to the injection pump?


And you said you checked the fuel shutoff solenoid. How did you check it?

[Msamsen]

Originally Posted by twistedtree

OK, so it's possible the generator wouldn't start because of whatever stopped the mains, but it also could be something else. So let's just keep that in mind.


You said you bled the gen fuel system up to the injector lines, so where the injector lines connect to the injection pump?


And you said you checked the fuel shutoff solenoid. How did you check it?

Sorry, I meant where the lines connect to the injectors. I have not touched the injector pump connections.

I removed the fuel solenoid and operated the switch to verify it physically opens.

[twistedtree]

OK. Another related check would be to crack one of the fuel pipe nuts at an injector, and try cranking with the Override switch engaged, and with it released. Fuel should squirt when the override switch is engaged, and stop when it is released.

[High Wire]

Has it been hard to start prior to this? If you are getting fuel to the injector tubes, it’s time to do a compression test. Remove the glow plugs and connect there. Should be 425-475 psi. My old westerbeke had similar symptoms. Compression test showed 275# in all cylinders. The cause was piston rings fused to the pistons from carbon.

[Msamsen]

Originally Posted by twistedtree

OK. Another related check would be to crack one of the fuel pipe nuts at an injector, and try cranking with the Override switch engaged, and with it released. Fuel should squirt when the override switch is engaged, and stop when it is released.

If you mean the supply line pipe nuts at each injector? I have, but only with the override switch on.

[Msamsen]

Originally Posted by High Wire

Has it been hard to start prior to this? If you are getting fuel to the injection pumps, it’s time to do a compression test. Remove the glow plugs and connect there. Should be 425-475 psi. My old westerbeke had similar symptoms. Compression test showed 275# in all cylinders.

It wasnt hard to start ever before this. Always about 2-3 seconds of cranking.
I will try a compression test next though.

Thanks!

[Msamsen]

One interesting observation during the lift pump check. The manual lever doesnt pump fuel. I took it off and noticed the plunger is aleady half way up the stroke even at the bottom of the camshaft lobe, rendering the primer pump void. It seems to be about a 1/4" until the plunger would bottom out.

[Msamsen]

Thank you for the advice! I will go there now with a remote start switch so I can see the fuel squirting in real time.

[twistedtree]

Originally Posted by Msamsen

Thank you for the advice! I will go there now with a remote start switch so I can see the fuel squirting in real time.

Part of what I'm trying to confirm is that the various control relays are working as expected.


On the lift pump, depending on where in it's rotation the engine stops, there can be insufficient stroke available in the pump for hand priming to work. If this is the case, just bump the starter to turn the engine a bit, and it will probably work fine. You should be able to feel it in the level when it builds some resistance as it moves fuel. So maybe try that part of the bleeding again?


Otherwise, I'm starting to run out of ideas too, as it does indeed seem you have done all the right things.

[Msamsen]

Originally Posted by twistedtree

Part of what I'm trying to confirm is that the various control relays are working as expected.


On the lift pump, depending on where in it's rotation the engine stops, there can be insufficient stroke available in the pump for hand priming to work. If this is the case, just bump the starter to turn the engine a bit, and it will probably work fine. You should be able to feel it in the level when it builds some resistance as it moves fuel. So maybe try that part of the bleeding again?


Otherwise, I'm starting to run out of ideas too, as it does indeed seem you have done all the right things.

Yes I tried bumping the motor and still no manual pump action. Upon removal i discovered the lift pump mounts with its plunger already about half way up the pump stroke, even with the cam lobe at the bottom. This may be why its not starting? Possibly insufficient fuel delivery from the lift pump. (maybe the new pump has a longer shaft than the old pump but unfortunately the old one got kicked and fell in the drink).

[Msamsen]

Besides the shutoff override, what other control relays should I be checking?

[twistedtree]

The Run Relay is the key for getting it started, and obviously the Starter Relay. If the fuel solenoid activates when you engage the override switch, then the Run Relay is working.


So was the lift pump recently changed? Was it changed as part of this effort? Has the gen run at all since replacing the lift pump?

[twistedtree]

Regarding things like compression and valve adjustment, they can lead to hard starting, but I think are unlikely to suddenly cause a no-start on a generator that has been previously starting OK. They lead to more of a slow decline in performance, so I doubt they are the immediate issue.

[Lepke]

You have a problem bigger than the generator. They have a gear pump with lots of suction. Detroit 453s pump much more fuel than they burn. You can suck minor amounts of air w/o any sign. In 60 years the only times I had to "bleed" a Detroit was a new or newly rebuilt engine with no fuel or once when a fuel line rubbed a hole.

Since it effected the Detroits, you need to closely inspect and question the entire fuel delivery system. Just because it worked in the past doesn't mean the design is good. The fuel route could have built in air locks.
I think you're at a point where the Detroits can deal with the air leaks or fuel restriction but the generator can't. I don't suppose you have a vacuum gauge between the primary filter and engines?

At this point you need to inspect the fuel line runs, every fitting, and every connection.

[High Wire]

Another thought is the gen fuel pickup. Does it tap off the fuel supply to the main engines or does it have its own outlet from the tanks? Sometimes the separate gen fuel tap ends higher in the tank so that running the gen out of fuel won't leave you stranded.

[Msamsen]

Originally Posted by Lepke

You have a problem bigger than the generator. They have a gear pump with lots of suction. Detroit 453s pump much more fuel than they burn. You can suck minor amounts of air w/o any sign. In 60 years the only times I had to "bleed" a Detroit was a new or newly rebuilt engine with no fuel or once when a fuel line rubbed a hole.

Since it effected the Detroits, you need to closely inspect and question the entire fuel delivery system. Just because it worked in the past doesn't mean the design is good. The fuel route could have built in air locks.
I think you're at a point where the Detroits can deal with the air leaks or fuel restriction but the generator can't. I don't suppose you have a vacuum gauge between the primary filter and engines?

At this point you need to inspect the fuel line runs, every fitting, and every connection.

Thanks Lepke!
I do have vac gages on each filter that shows filter restriction but not after.