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Air in the Fuel Line

Jan 22, 2008
32
Ericson 29 tall rig old orchard beach, maine
Hi folks,
I have a 1988 Catalina 20 mk2 with a universal Diesel M25. I have replaced with NEW the dip tube in the tank, the hose to the Racor the Racor and hose to the Electric lift pump and the pump and the hose to the engine. all are new. I also replaced the seal and filter on the 2ndary fuel filter. AS I understand it this is all of the supply side of the fuel parts. So there should be no air getting in here and yet I still have air in the fuel. After it goes to the engine it is under pressure so air should not be able to get in. To get the engine to start I have to prime the injector pump with fuel by the electric lift pump. Then I have to crack an injector nut at the injector pump and start the engine. then she starts right up. Sail for several hours and she starts right up. Leave it over night and I have to bleed it again. Any ideas ???? Help I have $2k into this and I am no better off then before.
 
Jul 14, 2015
840
Catalina 30 Stillhouse Hollow Marina
Bleed, bleed, bleed. It is a pain, but it only takes a tiny bit of air.
 
Jan 30, 2012
1,054
Nor'Sea 27 - "Kiwanda" Portland/Anacortes
Air is coming from the side where suction occurs --- a fitting, joint, clamp, whathaveyou between the tank and lift pump. Check particularly the primary filter and its fittings including the little primer pump if you have one.

Charles
 
Jan 30, 2012
1,054
Nor'Sea 27 - "Kiwanda" Portland/Anacortes
Second thoughts.

If it is leaking down only after sitting then you also need to consider the fittings after the lift pump. Chief among them the guard filter, its bleed screw and the screw gasket. If copper ring seals are encountered any place along the line remove and anneal them or replace them with new.

Charles
 
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Nov 6, 2006
8,872
Hunter 34 Mandeville Louisiana
An often overlooked possible air leak location is the packing of the fuel shut-off valve on the tank. The little nut where the valve stem goes into the valve body.. You can sometimes carefully tighten the packing by holding the valve (so ya don't crack it off the tank) and tightening the nut by a flat or so. If the valve has O-rings instead of packing, the nut will not move..
 
May 24, 2004
6,543
CC 30 South Florida
You seem to have a sizeable leak if it develops overnight. Where air comes in fuel should be leaking out. Clean and dry all lines, connectors and fixtures and then let it sit overnight and check for a small fuel leak next day. Do I gather correctly that you have a mechanical lift pump in there? I would by-pass it for testing purpose, just to eliminate the possibility of a ruptured diaphragm. I'm a little weary of add-on fixtures to the fuel system; they just seem to add more possibilities for leaks to develop. Check connectors and seals at the Racor, check the bleeding screw seal at the secondary filter, check connectors at the electric pump and the body for leaks. Concentrate in the injector pump area looking at the connectors, bleed screw seal and gaskets.
 
Apr 13, 2007
142
Catalina 27 TR Lorain, Ohio
I just had the same issue with my Universal M-18. All new lines, filters, electric lift pump, fittings and clamps. Ran great with no problems for the first 6 weeks. Then would stall or not start unless I bled the lines at the injector pump. Went through, tightened all the clamps, check tank vent for blockage, tank line for blockage etc. All OK. I then replaced the tank fuel shutoff, which i never close, with a pipe nipple. Problem seems to have gone away. That was most likely the cause of the air leak and 30 years old. There is an o ring seal that I could replace, or not. Maybe go with a new 1/4 ball valve or just leave the nipple in place.
As a side note: Did you do this work yourself or hire it done? Did they use teflon tape on the NPT? If so, that is very bad. Teflon tape can and will flake off and clog filters or even get into injectors. Never use this stuff on fuel lines. OK for water plumbing or Natural gas lines. I've seen people use it no straight thread fittings. Really bad idea. Those seal are metal to metal or seal with an O ring. Teflon tape just gets in the way of proper tightening. Telfon for tapered (pipe) thread only.
 
Apr 2, 2011
185
Catalina 27 Niceville, FL
Do you have a bleed bypass valve on the injector pump or just a bleed port? The most likely problem is probably a crack in the primary filter assembly. Either the base of the filter or the fuel line fittings. Changing parts until it is fixed is an expensive way to go. There are some simple troubleshooting methods, but start with the bypass valve.
 
Jan 22, 2008
32
Ericson 29 tall rig old orchard beach, maine
I have replaced every part between the tank and the injector pump and I still have the same issue. All brand New.
 
Jan 22, 2008
32
Ericson 29 tall rig old orchard beach, maine
I have replaced every thing on the supply side with new. I do not have a manual lift pump it is electric and new. I have not looked at the fuel shut off. Bye the bye I had all this done at a marina in Falmouth Maine (Handy Boat Service) where they are the Premier sailboat center in southern Maine. Should be the best work in the state.
 
Jan 22, 2008
32
Ericson 29 tall rig old orchard beach, maine
We as sailors get caught up in nomenclature all the time....I am not familiar with the term "Primary Filter". Do you mean the Racor? or the 2ndary filter on the engine? In either event. I replaced the Racor with a Brand new updated version. I replaced the Electric Fuel lift pump with new. I replaced the 2ndary fuel filter on the engine with a new o-ring and filter. Please explain. As to "a bleed bypass valve" on the injector pump or just a "bleed port" am not sure. I have a thumb screw attachment on the injector pump that turns the fuel on or off (I think) I had thought it was a fuel advance but it is not. I have it closed now as this is where it belongs. I don't use it. So what is it for? Your thoughts are good stuff. Please explain a little more in detail for us non gear head types. I am only now getting an education in Mechanics. S
 
Jan 22, 2008
32
Ericson 29 tall rig old orchard beach, maine
Do any of you think that there could be an issue with the injector pump? It is my impression that because it is on the pressure side of the fuel lines...air can not get in. Ordinarily the injector pumps are out live the engine....! Also it is a very expensive part to take off send out for rebuilding and replacement on my engine and I do not want to do this if it is not necessary.
 
Jul 14, 2015
840
Catalina 30 Stillhouse Hollow Marina
I had air getting into mine at the bleed valve in this picture. Not where my finger is pointing, but about an inch toward bottom of photo. I opened fully and bleed for a minute while pump running and closed again tight. Never had issue again.
2016-06-17 13.28.25.jpg
 
Apr 2, 2011
185
Catalina 27 Niceville, FL
We as sailors get caught up in nomenclature all the time....I am not familiar with the term "Primary Filter". Do you mean the Racor? or the 2ndary filter on the engine?
Your system should be tank to primary filter (usually a Racor), to fuel pump, to secondary filter (mounted on engine), and then to injector pump.
I had air getting into mine at the bleed valve in this picture. Not where my finger is pointing, but about an inch toward bottom of photo. I opened fully and bleed for a minute while pump running and closed again tight. Never had issue again.
That is the fuel bypass valve. With it open, you should hear the pump click more rapidly. When closed, the pump will slow down. That's all you need to do to bleed the M25/M25xp. Normally, you should never have to bleed the injectors.
Here is a simple test. You might need a helper on a C30. Disconnect to return line from the fuel tank and place it in a glass jar. Turn on the electric fuel pump but don't start the engine and open the bypass valve. You should get a small but solid stream of fuel. If you get any foam, you have an air leak. If the stream is sporadic, then you have a blockage. Once you have seen the symptom, you will also know when it is fixed.
 
Jan 22, 2008
32
Ericson 29 tall rig old orchard beach, maine
DSCF1806.JPG
Thanks for clearing up the terms. As I have stated before I have replaced every part between the tank and the engine. The dip tube(I think that is the name) the fuel line to the Racor, the Racor itself, the electric lift pump and the hose to the ending...they are all new. I have a knob like that on the injector pump that is similar. If I understand you that knob is the a bleed value? If so would it be possible to turn the key (not to start it) get the electric pump working (clicking) open the knob all the way and air and fuel will come out of the engine? However, if I understand you I will not see this operation. I will close the valve after a monument or two and that should bleed the system once and for all. At which time it should start right up? I will try this first and then if it does not do the trick I will try the trick with the return line. Thanks for the help. I will be in touch.
Steven
 
Jan 22, 2008
32
Ericson 29 tall rig old orchard beach, maine
See the picture of my engine. See the knob on the injector pump too. Is that in fact a bleed screw?

Steven
 
Jul 14, 2015
840
Catalina 30 Stillhouse Hollow Marina
See the picture of my engine. See the knob on the injector pump too. Is that in fact a bleed screw?

Steven
Yes, that is bleed valve, but you should see fuel when you turn key on and open the valve.
 
Jan 22, 2008
32
Ericson 29 tall rig old orchard beach, maine
I will give it a try next week end and see if it makes any difference. thanks.