Air in fuel line after shutdown - normal?

[incognico]

Hi all,

YD25. I was chasing some "injector rattle" noises and changed out filter/lines/clamps. To be confident the system was airtight I installed a [temporary] clear hose before the fuel pump. When running, this line is completely full and there are zero bubbles evident. It looked perfect. However on shutdown, there is immediately a large air bubble visible in the line, as per the attached pic. Is this normal? It starts fine from this condition. I am wondering if this air is being trapped in the pump somewhere while running and just needs to be bled better, or if there's some sort of setup (auto bleed thingy?) that lets the air in after shutdown.

Cheers,

--Nick (Busselton, WA)

 

[Old.Tony]

Air is unwanted, as the fuel pump relies on diesel to lubricate its internals. Try pumping the primer bulb a few times and see what comes of it. It's possible that you have a faulty (rubber deteriorates) primer bulb, or the water sensor in the fuel pump hasn't been clicked all the way home, or the little o-ring in the water sensor has debris or damage.

 

[incognico]

Appreciate your thoughts, thanks. It appears (yeah been wrong before) as though the air is coming from the engine-driven fuel pump "end" and not the filter/manual-lift-pump "end". I will loop up some clear hoses at each site to create some high points and gather a bit more information. I'm going to assume this is likely not normal based on your comments, and try to figure out where the air is either hiding during running or getting in from at shutdown.

 

[incognico]

For completeness I'll follow up on this now I have a result... the air I detected was not because of any faulty component. Air in the fuel line on the right/pump side of the engine (it is almost impossible to bleed in the OEM configuration) is trapped there and does not clear by itself. The vehicle starts and runs as normal. I had to get creative with some new hose routing and fittings so that I could confidently bleed this air out of the fuel system. With that gone, I could bleed the injectors at the hard line flare nuts and they don't immediately get more air from the huge pocket sitting somewhere in the fuel pump. My loud "injector rattle" is completely cured. Instead of a bag of spanners falling down an escalator, my engine is super quiet - seems like a different car. VERY happy with that.

 

[Azi]

Well done, I think a lot of D40s have that issue. Like you said air can be trapped in the system for a long tme and occasionally cause fuel starvation under load once a while.

 

[samt9892]

For completeness I'll follow up on this now I have a result... the air I detected was not because of any faulty component. Air in the fuel line on the right/pump side of the engine (it is almost impossible to bleed in the OEM configuration) is trapped there and does not clear by itself. The vehicle starts and runs as normal. I had to get creative with some new hose routing and fittings so that I could confidently bleed this air out of the fuel system. With that gone, I could bleed the injectors at the hard line flare nuts and they don't immediately get more air from the huge pocket sitting somewhere in the fuel pump. My loud "injector rattle" is completely cured. Instead of a bag of spanners falling down an escalator, my engine is super quiet - seems like a different car. VERY happy with that.

Hi Incognico, I know this is an old thread but I'm having similar injector rattles and have a bubble in the same line, any chance you can detail your method / hose setup for getting the air out the fuel pump?

Cheers
Sam

 

[rihi365]

Hi samt9892, did you get a reply on that? I think I have the same issue and would appreciate any help on that matter.

 

[samt9892]

Hi,

Nope no reply yet. I'm sure he would reply publicly on here if still following the thread