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Discussion Starter #1 (Edited)
So I'm new to having a diesel and I wondered the other day why my fuel pump continues to "purr" along with the ignition on, but the engine not yet started. It's a 1987 Catalina 30 and everything is in good order. The valve on the fuel return to the tank is closed so I figured that the pump would pump until it came up to pressure and then stop - kind of like my old 1967 MG Midget where I would listen for the pump to purr and then stop before I started the engine.

So am I just needing to get used to the purr continuing or should it actually stop? I'm wondering if the pump is starting to reach its life's end.

Oh, one other thing. When I open the fuel return valve the pump speeds up so I know that the fuel is running back to the tank. The engine runs fine by the way. I've replace the fuel lines last fall and everything went fine. I was getting ready to replace the filters this spring when I noticed the continuing noise and I can't remember if it was always there.

Any ideas?

Thanks,

Jeff
 

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Discussion Starter #3
I like how you're assuming that I have a spare pump. New to me boat and I'm still getting the spares sorted out. Must be time to order one.....
 

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There's nothing wrong with your pump. In the electrical system, it is designed to run all the time. If you have an M25 engine, the knurled knob can be kept closed. The pump will still run.

Poke around here (and read about bleeding, too)

Engines 101 - The BIGGEST & BEST collection of M25 Series Universal Engine Information on the Internet, plus some M35, too :)

Diesel Engine - C34

Bleeding 101 http://c34.org/bbs/index.php/topic,6377.0.html
 

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Why would the fuel return valve ever be closed?

For a moment, when I read about a continuous purring noise, I thought you might have been hearing the engine room ventilation fan.
 

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Discussion Starter #6
Thanks for all the help!

It 'sounds' like it's normal then, but I've now got a simple spare for peace of mind. I guess that the only reason to keep the return valve open is to either bleed, which I've accomplished, or to polish the fuel. I wouldn't want to put any unnecessary wear on the pump if it's not needed though.

I've got a few hours of motoring this weekend to move the boat and I'll likely polish the fuel with the valve open before I change the Racor and main filters. After our long New England winter with the fuel topped off and Enzyme Treatment added it seems like a good idea.
 

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I think you are confused. The valve in the fuel return line should be left open. The supply pump is sized to deliver more fuel than the engine uses at full power and the "extra" goes back to the tank. Do not run with the return valve closed.
 

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I would think the motor would flood with fuel, if you left it closed.
 

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Normal operation , the pump would soon build up max pressure and hold it,clicking once in a while as engine takes what's wanted or it's internal spring loaded release valve leaks back.If it clicks fast ,it's either moving fuel down the line or back-pedalling internally. When I use it for filling day tank(no line blockage) it whirred. When I ran it direct to carb of stove the occasional clicking told me rate of burn . Same applies as an engine app;ication. Think solenoid pushing a spring loaded piston with leaky valves.
 

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Discussion Starter #10
I'll do some debug this weekend. Basically it's either supposed to bleed back to the tank or not. At this point it's pretty unclear if it's normal. Len, I understand everything you've said and I do believe it's a leaky valve somewhere.

The bleed valve just before the injector pump should just be used for bleeding. I think I'm correct in that. If not somebody can explain why it should be open because unless you're polishing the fuel or bleeding there's no reason to leave it open. The pump should provide a set pressure and stop unless something is leaking back or there is a pump diaphragm or valve issue.

Just my thoughts.
 

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Discussion Starter #11
Here's a good thread on fuel return to the tank. It sounds like it should be very little and I'm assuming that it only occurs while the engine is running.

http://www.sailnet.com/forums/diesel/97726-return-diesel-fuel-tank.html

I guess it's time for me to plug the fuel line at the injector pump and see what happens. If the pump continues to run it should be either a faulty pump or air entrapment in the pump. Another thought is the possibility of it sucking air from either the pump strainer gasket or a fuel line upstream of the pump.
 

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More than likely you have a 1987 Universal M25 in your Catalina. The picture above is of a Facet fuel lift pump. This pump has a filter in the bottom, by the way.

The fuel tank should have 1 petcock for the fuel OUT line. This line should go to the Facet fuel pump pictured. From there the fuel should go to the Raycor filter, and it does because I can see it in your pic. From the Raycor, the fuel should go to a second (finer) fuel filter, and then up to the high pressure injection pump.

Assuming that you have an 86, or newer M25, there is a bypass valve on the inlet to the high pressure injection pump. The bypass valve allows fuel to bypass the high pressure pump, and to directly enter the fuel injectors at relatively high volume, and low pressure. This valve is there to allow you to EASILY bleed the system. In normal operation, the valve should be closed, and the lift pump should "tick" at a rate of about 1hz. When the valve is opened for bleeding, the lift pump will "tick" at about 10hz.

When fuel gets to the high pressure pump, it is forced at very high pressure (1991-2300 PSI) and low volume into the metal injector lines at EXACTLY the right time as the crankshaft rotates. This pump is driven by a "fuel camshaft," and there is a procedure for fine tuning the timing if necessary. The high pressure forces the injector to open, and forces some fuel into the combustion chamber.

Some fuel, however, is supposed to leak past the injector nozzle, and is used to cool and clean the injector. This fuel, which misses the injector nozzle, backflows through the injector assembly, and enters into the fuel return line. The return line daisy chains across all three injectors, and then returns the unused fuel to the fuel tank. There is no petcock on this line.

Here is a GREAT video that explains the injector;

The M25 uses a pintle type injector.
 

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Discussion Starter #13
Thanks for all the info. I couldn't see the video, but I know the basic workings.

I knew about the lubing of the injector, but I didn't think it would be that much especially with the injectors not firing when the engine is off. I've got the spare pump now so it will probably last forever vs not having a spare.... I'm still going to test the pump with the line blocked off to see if it stops and I'll see if I can scrounge up a 0-10psi gauge to test the pressure.

I'll report my findings.
 

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You may have a bad bypass valve...
 
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