my boat lister engine keeps losing and gaining revs . it has air in the system why?

Question

when i undo nut on top of filter loads of air bubbles come out with the diesel , i have left the nut undone for ages and air just keeps coming out . how do i eradicate this problem, it is a fishing boat and i need to get it fixed as it worries me when im at sea . it has done it for a while but it is getting worse every day, please can sm 1 help

Answer 1

sounds like you have a small "pinhole" leak in your fuel intake line... perhaps if you replace the lines that lead from your fuel source this will fix your problem. Check all clamps also, at all the connections along the way if it is metal it may have gotten " rubbed" and if it is rubber they wear out even more quickly... Good Luck!

Answer 2

Hope texblueskypilot has the answer, thats the easy one.
Once came across a Lister with running probs, air in filters etc. and although not terminal it was a big job.
The injector seals where they enter the cylinder tend to rot which cause the ingress of air to the fuel system and it`s apartial strip down to replace them. The good news is that diesel drains into the sump, so the oil level will be up if this is the problem. Good luck, hope its just dodgy pipe or clips.

Answer 3

That is the secondary filter Check the primary filter for leaks.Have had Racors bad plastic cups or with a leak you can look at it with the Eng running an see a very tiny stream of air only leaks when running use flash light on the side>Also check the return lines see if 1 is lose our cracked .take the lift pump an bleed the Inj pump. also the pickup tube in the tank can get a tiny hole in it sucks air. try a remote tank an see if the air stops.That will keep you busy>hope this help.

Answer 4

Somewhere between the fuel tank and the engine, there is a small leak in the fuel line. Take the line loose where it connects to the tank, and apply a small amount of air pressure towards the engine. (yes, you will need to bleed the air out of the line later, no big deal) and go along the whole fuel line with soapy water and look for the soapy bubbles to form where the leak is!

It is most likely either a rotted rubber hose or a metal line that has rusted through.

Answer 5

She's deffinately sucking air somewhere. If you don't find a bad line, replace the fuel filter, it may have a bad gasket seal. Make sure you fill the new filter with fuel before installing it. Also check any brass fittings that may have cracked due to over tightening.