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Calcruiser 30-04-2020 08:21

Air in fuel line
 
Howdy,

I’ve read every topic on this I think, but can’t find a good answer.
I have a universal M3-20b diesel. After I got it the fuel line would need bleeding before starting. The engine would start and run for 5 seconds before dying. I would bleed the fuel and the electric lift pump would click and a little dribble of fuel would come out. This is my first diesel sailboat so I have no idea how much fuel should be moved by the pump when bleeding. After this, the engine would start right up and run fine.

Not wanting to bleed the engine every time, I replaced all the fuel lines except the one from the tank to the racor. It’s hard to get to and the pickup tube seems to not be removable on the plastic tank. My system is. Tank—racor—lift pump—engine mounted filter—-bleed screw—high pressure pump.

I also replaced the fuel filter. It seemed a bit dirty for a 600hour engine.

After the fuel lines and filter were replaced, I bled the fuel line and the fuel GUSHED out! Great I thought, I must have had a clogged fuel filter. Then, after a 2 month haul out, the same issue. I bled the fuel and it only dribbled. After an hour of that and bleeding for a minute and bubble coming out, something “broke free” and the lift pump made a different noise and fuel gushed out the bleed screw- started right up.

My plan is to replace the racor filter since it was only 2 micron with a 30 micron and replace the fuel pump as well.

My question is this, if this is the symptom of a Clogged filter or a failed pump, why would that result in an air leak???? Do I have a clogged filter AND and air leak somewhere? Do lift pumps fail by introducing air, or letting fuel drain back and letting air in? It seems when the engine sits, some air gets to the top of the line right before the high pressure pump. But how, when this doesn’t affect the engine running?

rbk 30-04-2020 08:50

Re: Air in fuel line
 
Have you inspected your tank and pickup? Might be clogged filter, pickup could very well be symptoms of dirty tank and fuel.

SVHarmonie 30-04-2020 08:53

Re: Air in fuel line
 
[QUOTE=Calcruiser;3129001]

First questions: Are you sure the problem is air? The symptoms you describe could just as easily be a funky electronic lift pump. I assume we are talking about one of those little impulse pumps. When I had an engine that used one of them I always carried an extra one, for me they were very unreliable. The good news is that they are dirt cheap...

You also missed a key piece of data bout your system: What is the height of the fuel level in the tank compared to the filter, and the lift pump.

Calcruiser 30-04-2020 09:49

Re: Air in fuel line
 
1 Attachment(s)
[QUOTE=SVHarmonie;3129021]
Quote:

Originally Posted by Calcruiser (Post 3129001)

First questions: Are you sure the problem is air? The symptoms you describe could just as easily be a funky electronic lift pump. I assume we are talking about one of those little impulse pumps. When I had an engine that used one of them I always carried an extra one, for me they were very unreliable. The good news is that they are dirt cheap...

You also missed a key piece of data bout your system: What is the height of the fuel level in the tank compared to the filter, and the lift pump.

Tank is totally above racor, line runs downhill to the lift pump pump goes up to screw on filter something around tank height. Tank is 1/3rd full.

I think itís air because bleeding it fixed the problem and the engine had no trouble once started. But, I have a new pump on order.

Iíll try and get to the pickup tube, but rotating it around it didnít seem to unscrew from the tank. Iím worried itís cast into the plastic tank or something. There is an elbow and a shutoff valve connected to the pickup tube. Closing the valve, the fuel lines hold air when I blow in a fuel line, but no way to test the elbow and pickup tube unless I take the whole tank out, which I donít know if that is possible without removing the engine.

GordMay 30-04-2020 11:37

Re: Air in fuel line
 
Greetings and welcome aboard the CF, Calcruiser.

SERVICE MANUAL*: Universal M3∑20B
Page 64 etc. ➥ https://www.westerbeke.com/technical...hnical_man.pdf

The Universal Diesels claim to be self bleeding. Good luck :nonono:

Most engines need to be bled in a specific order of components, usually following the sequence of secondary filter, injector pump, & injectors.
1. If you're replacing the fuel filter element, be sure it's full of fuel before you start bleeding.
2. While operating the the lift pump, open the bleed screw the secondary filter, and you'll likely see small bubbles coming through the bleed screw. Continue pumping until the bubbles stop, and clean fuel begins to weep from the hole. Retighten the screw as you pump.
3. Repeat the pumping procedure, loosening the screw on the injector pump.
4. Loosen the fitting, at the nearest injector. Do not unscrew it all the way. Then pump until the diesel runs clear, then re-tighten. Repeat on other injectors.

See alsohttps://www.cruisersforum.com/forums...er-164574.html

*I encourage anyone, who downlaods useful documents, from links (links often go ‘dead’ with time), to then upload the document to our
CF Document Library Downloads:https://www.cruisersforum.com/forums/downloads.php

SVHarmonie 30-04-2020 12:00

Re: Air in fuel line
 
[QUOTE=Calcruiser;3129063]
Quote:

Originally Posted by SVHarmonie (Post 3129021)

Tank is totally above racor, line runs downhill to the lift pump pump goes up to screw on filter something around tank height. Tank is 1/3rd full.

I think itís air because bleeding it fixed the problem and the engine had no trouble once started. But, I have a new pump on order.

Iíll try and get to the pickup tube, but rotating it around it didnít seem to unscrew from the tank. Iím worried itís cast into the plastic tank or something. There is an elbow and a shutoff valve connected to the pickup tube. Closing the valve, the fuel lines hold air when I blow in a fuel line, but no way to test the elbow and pickup tube unless I take the whole tank out, which I donít know if that is possible without removing the engine.

You have either a significant restriction in the fuel line, or a bad lift pump. Air will not be "leaking" in to a line with is always under pressure, which yours is from the head of the fuel in the tank.

Two possibilities inside the tank. One is a leak in the pickup tube above the fuel level. THAT would allow air in.

The other is a piece of crude floating around in the tank that periodically obstructs the opening when the pump is sucking fuel. It then falls away when you stop the pump and bleed the system. Making you think bleeding fixed the problem, until the debris gets sucked up again some random time later. (Ask me how I know about this problem!)

If you don't have a cleanout/inspection port in your fuel tank, now would be a good time to add one.

Calcruiser 30-04-2020 13:16

Re: Air in fuel line
 
[QUOTE=SVHarmonie;3129152]
Quote:

Originally Posted by Calcruiser (Post 3129063)

You have either a significant restriction in the fuel line, or a bad lift pump. Air will not be "leaking" in to a line with is always under pressure, which yours is from the head of the fuel in the tank.

Two possibilities inside the tank. One is a leak in the pickup tube above the fuel level. THAT would allow air in.

The other is a piece of crude floating around in the tank that periodically obstructs the opening when the pump is sucking fuel. It then falls away when you stop the pump and bleed the system. Making you think bleeding fixed the problem, until the debris gets sucked up again some random time later. (Ask me how I know about this problem!)

If you don't have a cleanout/inspection port in your fuel tank, now would be a good time to add one.

Thanks, in my case 'bleeding" means holding the preheat button for 20 seconds at a time to get the fuel pump to work, I have no manual lever.

I do think it's some blockage and I hope that the likely clogged racor replacement will solve the problem, BUT, won't I still have some air leak? If the pump is sucking hard against some obstruction and some air is getting in, when I remove the obstruction won't air still get in the same place - just maybe less? That's why I'm hoping someone says "your lift pump will introduce air in when it is failing."

Cat36Mahalo 30-04-2020 16:14

Re: Air in fuel line
 
Your correct in ditching the 2 micron filter, they cause lift pump failure. Beyond a plugged pickup tube the lift pump filter could be clogged, or your vent line is clogged (bees, kinked hoses...). Where are you bleeding the line - that the fuel gushes or dribbles?

Calcruiser 30-04-2020 16:33

Re: Air in fuel line
 
1 Attachment(s)
Here in the photo is the bleed bolt. The pump is bolted to the engine and hoses connect it to the screw in filter and another hose goes to the banjo bolt on the engine, this bleed bolt, then hard lines go to the high pressure pump/injectors.

The bolt is just below the air filter in the upper left of this photo(if it was straightened) itís just after the banjo bolt on the hose coming from the screw in fuel filter.

doog 01-05-2020 11:45

Re: Air in fuel line
 
Its very common to have debris in the fuel tank which collects around the intake of the pickup tube and very difficult to clean and remove. You blow out the line but it just clogs again, usually a fine screen filter on the inside of the standpipe..

I had an old genset with this issue and impossible to get the particulate our of the tank..so I shoved a peice of air filter type foam which is fuel friendly..and very porous, in place above the fuel inlet, and this blocks the debris from entering and clogging the line but allows the fuel to flow through freely.

The issue is that tanks often corrode internally and the flakes cannot be extracted because there is no hole at the low point..You can vacuum and go nuts but never get it all..This foam pad is one solution that works..And this is likely what you're up against..

You'll sort it out..

DougR 01-05-2020 13:03

Re: Air in fuel line
 
All of the above, plus.......

Remove and clean that 90degree street elbow at the top of the pickup tube. That's a fruitful place for debris to lodge and cause problems.

sck5 01-05-2020 13:06

Re: Air in fuel line
 
replace that 2 micron filter. way too fine for a fuel line

Dam Yankee 01-05-2020 16:25

Re: Air in fuel line
 
We have an M3-20 in our boat, and had a problem with air into the Racor filter - which was evident by air bubbles in the clear bowl of the Racor. The problem was found to be the pick up tube fitting into the tank was not tight. We have had problems with algae in the tank as well, but usually this results in a clogged Racor filter. Our M3-20 actually has two bleed locations - 1st on the secondary filter, and the 2nd on the input to the injector pump. Do the secondary filter 1st, then the injector pump.

Cat36Mahalo 01-05-2020 17:19

Re: Air in fuel line
 
That’s like the bleed bolt on my early M25. I swapped it out for a “knurled nut” which routes that flow back to the tank. I personally leave the valve open 1/4 turn all the time which helps with air. I still think you have some kind of restriction.

sailon46 01-05-2020 17:32

Re: Air in fuel line
 
While you are checking around look at your vent and make sure is not clogged that can also cause dribbles and gushers and do on as you describe.
Ernie on the Mary Jane


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