Air in the fuel system.. suggestions

[NYSail]

Hello all,

Last night while motoring in from a beautiful night sail with the wife, the engine stopped right in the harbor channel. Friend happened by, I threw him a line and was being towed in. I new the problem was air in the fuel lines (Yanmar 3HM35F). I went below while wife was at the wheel and bled the system just in time to turn into my slip. So where is the air coming from. This actually happened last year 1 time when I brought the rpm's above what I typically do...... This year I have taken a few long trips with engine running perfect at high rpms for many hours straight.

- All new hoses and clamps 4 years ago and still looking new, checked and tightened every year.
-Primary Raccor 500 all tight

However I notice a small amount of fuel around the gasket of the manual fuel pump. This is in an awkward space with access to the top screws (4) difficult to manage, however I do tighten them each year... but still the gasket has a "glisten" of fuel. So I think a rebuild or replacement of this is in order including the braided fuel hose leading to the secondary filter.

All bleed screws have been replaced and are also checked each year.

Also, I have thought about the tank, specifically the pick up. Could this part get clogged causing problems. I have never pulled this to check. Raccor bowl has minimal sediment which I assumed to mean tank is relatively clean (trips every year include some wild bumpy rides to churn up bottom debris)

So what say all on this... anywhere else I should check?

Thanks!!

Greg
s/v Four the Soul

 

[Stu Jackson]

Yup, if you see a leak, fix it. It could be in a position to intake air into the system, right?

 

[NYSail]

Thats my thought. Any thought about fuel tank pick-up?

 

[Don S/V ILLusion]

It's possible but unlikely the pick-up tube is sucking air. I'd go with the visible leaks first and if that doesn't eliminate the problem, it might indicate a fuel starvation problem which goes back to your pick-up tube question but for a different reason - clogged?

 

[Dan Johnson]

Re: Air in the fuel system.. suggestions...

Agree with Don and Stu that you should fix any leaking issue first.

Here's some additional problem-solving questions:

How full is your fuel tank when this happens?

Where is the tank located in the boat?

Where is the pick-up located in the tank?

How deep into the tank does the pick-up tube go?

Does the pick-up tube have a screen on its end?

 

[Slow Mo^cean]

Any visible leak in a diesel system is a good place to start, especially in the high pressure system (after the injection pump). Low pressure system leaks typically have hard starting issues and reduced fuel economy, but rarely kill an engine (unless its a big leak).

 

[Bob S]

I chased an air leak most of last season. it turned out my Racor housing which is powder coated had chipped where the filter gasket seats on the housing. I used a piece of Emery cloth to sand it smooth to create a seal. Drove me crazy trying to find it. Good Luck!

 

[rardiH36]

What was your fuel tank level both times?

I ask because last year my engine cut out about one minute after starting and then wouldn't restart when I was in very choppy water surface conditions. The fuel level at the time was a little less that 1/4 tank. Still about 6-7 gallons, but maybe only about 6" left in the bottom of the ~24" tank. This was the lowest I had ever let the capacity get. Sailed under wind power to a safe anchorage (and calm water) and eventually bled the system good enough to start. I'm pretty sure that the rocking of the boat cause a momentary suck of air instead of fuel.

I used the problem to 1) Never let the fuel level drop so low again. 2) As you did, I took a hard look at my fuel delivery system. Replaced all gaskets, banjo washers and hoses. Afterwards, my 2 cylinder engine is running much smoother with less vibration than anytime since I bought the boat. I expect that I did have air ingress somewhere for a long time. Not enough to cause the engine to not start or not run ok. But enough to cause an uneven fuel supply to cylinders and uneven vibration.

 

[NYSail]

The leak does not actually leak as in drip... just I can see a wet gasket and that is enough in my mind to cause air. This pump though is before the injector pump. Maybe it is sucking small amounts over the season and just now finds enough to cause a problem.

 

[Stu Jackson]

Sounds right, exactly right.

 

[Ray Bowles]

NYSail, It takes a fairly large shot of air to shut the engine down entirely. Did the engine simply quit, no sputtering, just quit? Or did it stumble, sputter and then die?
An air block that causes a total shutdown, without some symptoms of fuel starvation, needs a place for that air to build up in before it is strong enough to move through the system and shut it down.
A fuel delivery problem can shut the engine down without warning and is usually something much different than an air leak.
Based on your description of the problem I think that at high RPM you have stronger fuel pressure and therefor more volumn and it runs fine. At lower RPM you have lower fuel pressure and that can shut the engine down like you said. Low pressure and the injectors don't squirt. Do you have a fuel pressure gauge? If so what did it read?
You might want to install a gauge if this continues to help further investigate what is happening.
Good luck, Ray

 

[Mark Maulden]

You can armchair quarterback this forever. How far below the engine is the fuel tank? I'd remove the pump which sounds like an engine driven pump. (via a cam lobe)? Rebuild it and reinstall it. Before reconnecting, put a pressure gauge on output and turn engine over. You should get about 6 lbs. These lift pumps can work pretty hard if the tank is low. After that, take the time and start at the fuel pickup and work your way to the injector. It was amazing what I found and it was easier to just buy a chunk of fuel line and fittings and re do it especially if your boat is "old". As an example, I had a small shutoff valve just before the primary filter which I think was pulling some air at the shaft. Just easier to replace.

 

[NYSail]

You guys are great....
1 - tank is about half full
2 - all hoses and clamps are new as of 4 years ago

When the engine cut out... it did not just turn off. All of a sudden there was a drop in rpm's and over about 10 seconds decended to shut off. When I opened the bleed value on the injector pump I could hear the air. All it took was about 5 pumps and only fuel was coming out (no bubbles).

I have never opened up the fuel tank to inspect / clean pick-up tube... will do this weekend.
The obvious is the "manual" fuel pump that is on the low preasure side right before the secondary fuel filter.... I have been looking at this since last summer and have thought that the tightening I was doing was good enough (I knew beter and was fooling myself). The part needs to come out and be rebuilt / replaced. I will call my parts guy today and see the cost of rebuild verses new.
It could be that I am having a block in the pick-up tube that is causing preasure throughout the system as it pulls fuel and this causes air to be sucked in through the failing gasket?????
One item I do have that I never though twice about was an old fuel shut off switch in line... maybe I will spring $5 for a new one just for peice of mind.

Again thanks for the input... I feel this is pretty straight forward with only three items to address: manual fuel pump; rebuild/replace, get a new shut off valve and inspect clean the fuel pick-up.

I'll let you guys know Monday. In the mean time, have a great week and weekend of sailing!

 

[zeehag]

your problem sounds like mine when i had a fuel air leak. we spent 3 days bleeding everything and found a hose clamp to my fuel assist pump was leaky. replaced that with racor system.... then found the banjo fitting that was leaking--fixed that--- did this for 3 days. i have a rebuilt 4-108 with no more leaks.....none from air nor fuel. we even repaired a fuel tube flange that was leaky--is fun- boating is fun--- repeat many times as you search for the leak-- good luck and have fun..

 

[sailaway78]

Air leak

If your getting air into the system while running, it is going to be at or before the lift pump. Behind the lift pump, the system is pressurized, and will not suck air.

 

[RichH]

However I notice a small amount of fuel around the gasket of the manual fuel pump. This is in an awkward space with access to the top screws (4) difficult to manage, however I do tighten them each year... but still the gasket has a "glisten" of fuel. So I think a rebuild or replacement of this is in order including the braided fuel hose leading to the secondary filter.

Such quite strongly suggests that either the diaphragm of the pump is ruptured/cracked and is sucking air from the crankcase, etc. or the gasketing that seals the pump body via the edges of the diaphragm is no longer intact. Rubber gasketing, and rubber diaphrams can easily deform after tightening. Constantly overtightening them without reason can 'cut' the rubber.

Id also check ANY 'compression fitting' in the system, as these in effect are 'one time only tightening devices'. The problem is that upon retightening of the outer nut, the 'ferrule' continues to compress into the SOFT copper tube ... and the copper easily deforms and 'relaxes' under continued strain. In industry where 'cheapy' compression nuts are installed, the usual practice in 'critical' systems is to always cut a bit of the copper tube back to where it wasnt compressed before any retightening. Double flared tube connectors dont have this problem.

FWIW - if you have a vacuum gage installed to monitor filter performance and WHEN to change a filter, a good way to check your work that you actually did solve a leak: Run the engine at WOT, close the TANK VALVE which will develop high vacuum in the fuel delivery line & Immediately shut down the engine ..... and note the vacuum reading of the filter gage. If the vacuum remains high over a considerable time with the engine shut down and the tank valve closed youve solved the leak. If the gage reading shows a lessening vacuum you didnt solve the air leak.

;-)

 

[Bob Mack]

If none of the above, I'd go back and check the fuel intake. A clogged intake screen can cause such a suction that leaks will be forced in other locations. Once tried for a month to identify a presumed air leak, when in fact, the final culpret was a clogged intake screen. Its easy to check and eliminate on most tanks.

 

[NYSail]

I bought a new lift pump and braided fuel hose and will install this weekend.... Also am going to pull the fuel pick-up and inspect. I will let the group know how this all goes when I am done.

Again thanks for all the opinions and advise.

Greg