Finding a Diesel vacuum leak ?

[TJM]

I have twin Ford Lehman diesels and about every 5 hrs of travel time my port engine runs out of fuel. When I bleed the system, my Racor 500's are full but I have air bubbles in my secondary's and injector pump. After a quick bleed we start up and go on our way.
My NL Genny is also having diesel "issues" with fuel starvation.

Is there a good way to check for vacuum leaks ? I am slowly replacing all of the older hoses and hose barb fittings and replacing with the Parker Hannifin hose with crimped on fittings.
I know there is a fluorescent dye for fuel leaks, but what about a vacuum ?

 

[sunchaser]

Install a clear fuel line in the suspect locations after the Racor and look for bubbles. Also disconnect your line to the Racor and draw from a jerry can to hopefully eliminate tank to Racors fuel line leaks.

Is this a new happening that started after some maintenance or filter change?Place some blue towels around the lift and injector pumps looking for fuel stains.

 

[jleonard]

I had a similar problem when I first got my Albin. The cause was the flex hose ahead of the lift pump was collapsing inside.
New lift pump and fuel line kit from ADC and never another issue.
Hope this helps.

 

[Barking Sands]

Vacuum leaks can be tricky to identify. Many times spots that leak under vacuum do not leak when internal and external pressures equalize. So at rest they don't identify themselves with static drips.

A clear hose for troubleshooting would be nice if you can find some that don't collapse under vacuum. Usually the ones that dont collapse have fibers or wires or other obstructions to viewing small bubbles. Also the section or fitting you put the clear tube in may affect those tests if those connections where actually where the leak was. But it could definitely be useful.

You can also plug/cap the line just prior to the lift pump (no need to check after the lift pump since thats all pressurized lines), evacuate the fuel in the line, plumb in shop air as far before the Racor as you can and slowly increase pressure using a regulator to just under the rating of the Racor (25PSI). Then use something like Snoop or soapy water to find leaks. Keep in mind that again, sometimes leaks under vacuum may not show under slight positive pressure. So you might need to turn up the pressure closer to the 25 PSI rating of the Racor. If you set up such a rig I would put a shut off valve near the regulator in such a way that if no leak is obvious using the Snoop that you can isolate that section of line with pressure in it, close it off using the valve and see if it holds over time. But generally you can find even very small leaks with a quality product like Snoop.

From my limited experience with the Racors...it seems the majority of time the issue is in the Racor. Doing the clear hose trick with a small section of clear hose plumbed in just after the Racor might be quick and easy to eliminate or include the Racor. If it shows air after the Racor move it to just in front of the Racor and see if its still there.

From there I think you just have to go through each piece, disassemble, inspect, replace as needed and reassemble.

I basically just did the same thing. Made some upgrades along the way. I converted everything to 37 degree flare though (JIC or AN)

 

[TJM]

Barking Sands great info.
Just to clarify my understanding. Everything upstream from the lift pump back thru the Racor to the tank is suction. Everything after the lift pump is positive pressure which would not introduce air into the system.

 

[FoxtrotCharlie]

We are having the same issue with our stbd FL135. Started about a month ago - we are on the Loop and it started in the middle of Georgian Bay, Ontario. Thought I had it fixed, but it started again. Back to the boat next week and will try to track the leak down

 

[Barking Sands]

Barking Sands great info.
Just to clarify my understanding. Everything upstream from the lift pump back thru the Racor to the tank is suction. Everything after the lift pump is positive pressure which would not introduce air into the system.

Yes...technically everything prior to the lift pump...all the way back to the fuel tank pickup tube that is above the fuel line could introduce air. But start with what's accessible and even then start with items we tend to service or touch. Such as the Racor.

 

[Slowmo]

I have the same problem with my generator, starving for fuel even with a new lift pump. After a bunch of experimentation it appears that the leak is in the Racor itself. My genny Racor has a priming pump on it and I'm suspecting that it is the source of the an air leak. When I bypassed the Racor I was able to prime and get fuel, but with the Racor in place I'd get air. It took me a long time to even consider the possibility that the filter assembly could ever be a problem.

 

[catalinajack]

I have the same problem with my generator, starving for fuel even with a new lift pump. After a bunch of experimentation it appears that the leak is in the Racor itself. My genny Racor has a priming pump on it and I'm suspecting that it is the source of the an air leak. When I bypassed the Racor I was able to prime and get fuel, but with the Racor in place I'd get air. It took me a long time to even consider the possibility that the filter assembly could ever be a problem.

Another reason I got rid of the Racors on my boat. What you see in the pic is from Tony Athens. Love it. Twenty micron to a 10-micron. Easy change. Gauges tell me when.