Bleeding Universal M12

[M275sailer]

Since changing a fuel filter my diesel will sputter and stall when at idle or shifting. I have bled it several times at the filter but it pursists. My manual mentions a bleed screw near the air filter. I assume this is on the high pressure side. Do I do this while the motor is running? Should the injectors also be done and how is that done with this type of motor? Any thoughts, Thanks.

[SteveInMD]

The bleed screw is for the low pressure system. You need to first bleed the low pressure side and close all the bleed points. Then open all injector connections 1 full turn. Crank the engine until fuel spits from all injector connections. Don't worry it will not start. When you stop cranking the fuel will not "run back" down the lines and suck in air. Then close the injector connections firmly. Then restart. If it still doesn't run right bleed the low side again, and then the high side.

[M275sailer]

So do the injectors get loosened below where the glow plug nuts are? I don't use the screw at the filter then, but use this other low pressure one by the air filter?

[Maine Sail]

Originally Posted by SteveInMD

The bleed screw is for the low pressure system. You need to first bleed the low pressure side and close all the bleed points. Then open all injector connections 1 full turn. Crank the engine until fuel spits from all injector connections. Don't worry it will not start. When you stop cranking the fuel will not "run back" down the lines and suck in air. Then close the injector connections firmly. Then restart. If it still doesn't run right bleed the low side again, and then the high side.

Steve,

Have you really ever needed to bleed the high side? In well over 100+ fuel filter changes on everything from Cummins, Detroit, Cat, Yanmar, Universal, Volvo, Westerbeke & more I've have never once actually needed to touch the high side or injectors...?



M275,

BLEEDING THE FUEL SYSTEM:

It will be necessary to bleed the fuel system to achieve a steady air free flow of fuel if any of the following have occured: Models M-12, M2-12, M3-20, and M4-30 have self bleeding fuel systems. 1. Running out of fuel.

2. If fuel shut off valve is left closed and engine runs out of fuel.

3. Replacing fuel filter.

4. Fuel injector nozzle or injector pump repair.

5. After repairing or replacing any fuel line.

6. Before putting engine back into service in the spring, if fuel system has been drained.

7. Replacement of electric or mechanical fuel pump.

8. Any time air is permitted to enter the fuel system.

BLEEDING PROCEDURE:

Be sure to have some means available to catch or absorb any fuel escaping during the bleeding process so that it will not accumulate in the engine compartment or bilge.
1. Be sure there is a sufficient supply of fuel in the fuel tank.

2. Open the fuel shut-off valve at the tank.

3. Start the electric fuel pump by turning the ignition key to the "ON" position on models 18,
20, 25, 30, 50, all models after 1986.

4. Model 15 has a mechanical fuel pump. Therefore with decompression on, turn engine over with starter. Crank at 10 second intervals while doing steps #5 and 7.

5. Slowly loosen the air bleed plug on the fuel filter, letting air escape until an air free flow of fuel is evident. (1986 models see item 7).

6. At this time, tighten the air bleed plug on the filter.

7. Slowly loosen the air bleed plug on the injector pump, letting air escape until an air free flow of fuel is evident. Units with a self bleed return valve, open for a short period then start engine, as soon as engine runs smooth close valve. Model-12 has continuous fuel bleeding.

8. At this time, tighten the air bleed plug or knurled knob on the injector pump.

9. The fuel system should now be properly bled and ready for operation.

Refer to starting instructions before attempting to start the engine after bleeding the fuel system.

CAUTION: Excessive cranking with sea **** valve open can cause water accumulation in the muffler and possibly back up into the engine. Drain muffler as needed.


The red arrow points to the injector pump bleed screw on my old M-25. Sorry I don't have any other pics to show you the fuel filter bleed screw. the M-12 may be slightly different.

[M275sailer]

Thanks Halekai, that bleed screw isn't as handy on my m12 since I haven't spotted it yet. Should be straight forward though. Do you know what exactly is meant by "has continuous fuel bleeding"?

[Maine Sail]

Originally Posted by M275sailer

Thanks Halekai, that bleed screw isn't as handy on my m12 since I haven't spotted it yet. Should be straight forward though. Do you know what exactly is meant by "has continuous fuel bleeding"?

Not really as I've never actually had my hands on an M-12. Perhaps they mean it is self bleeding?

My Westerbeke is self bleeding and it's a great feature. I change the filters and use a jumper wire to fire up the lift pump and in about 15-20 seconds the Racor is full and the pump noise changes from a fast click to a slower click and she's done.

You might want to check your filter installation and make sure you are not sucking air. You may have a kinked o-ring or something installed incorrectly..

[M275sailer]

Yes, I will check that if the bleed screw doesn't do it. As usual, I am greatfull for all the help I get here as I discover the joys of sailing.
-Gary