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Discussion Starter #1
I've read and followed all the discussions around air in fuel lines. I've been dealing with air in the fuel lines for many months, which is causing long cranking to build enough pressure to fire. Bubbles can be seen running from the filter to LP pump only after the engine and fuel warm up (15min). Very hard to start when warm, as I figure warm aerated fuel is harder to pressurise to fire up the engine. No sign of any fuel leaks
I've replaced; all the o-rings from the LP pump back up to the rail., the pressure regulator. Replaced an injector after a leak-off test and the fuel filter.
I tested the fuel coming from the tank- No bubbles but bubbles can be seen in the fuel return, which is expected. I'm always priming up the fuel filter with about 150ml of diesel after a long run, but air always returns. Engine runs just fine.
I'm about to dive into the lines that feed the HP pump. where would air be getting in the lines that feed the HP pump? Its a tight squeeze, so anyone with knowledge of this area would be greatly appreciated.

This may be the last time I attempt this repair, as I'm all out of ideas. Going to pressure test the soft LP lines for leaks too.
She's getting close to a Viking funeral if this air leak keeps up, so any insight could save her.
 

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Hello Vitomite,
The LP or lift pump sucks fuel from the tank. The way it is plumbed is unfortunate as the lift pump sucks through the filter assembly and all along the supply fuel line potentially letting air in if there is a leak..
I don't think you should waste your efforts looking 'after' the lift pump unless you see diesel leaking from the fittings. Before the lift pump, the filter and all the hoses and all connections from the fuel tank are under a slight vacuum during operation to suck the fuel from the tank. This is where the air is getting into the fuel lines.
After the lift pump, to the shut off valve (if fitted), then to the HP pump, the fuel is under pressure and any leaks will be seen as leaking diesel.
This is an annoying problem and the only way I know to solve is is with "BRUTE FORCE". By this i mean change every O-ring between the supply line and LP pump. Check and "cut back" the supply fuel line from the tank where it connects to the engine on the little block where the return line is also. You know, in front of the EGR. As a precaution, I also replaced the clear plastic fuel line from that little block to the filter. It wasn't expensive.
Good luck and don't forget to let us know how you went. :cool:
 

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Discussion Starter #3 (Edited)
Thanks Devito.

So are you saying there is no-where between the lift pump and the HP for air to be getting in? I noticed there are a few o-rings in that section. The line between the LP and the shutoff valve was my other concern. Its a bitch to get to, so I'd be glad to know if that section and lines cannot pull air. Do you know?

I have a replacement fuel line from the filter to the LP. I guess I can pressure test the other clear fuel lines to see if they have a crack or hole.

Like I said, the engine runs great still, its just the start-up and long cranking. But I know this problem won't fix itself and will eventually see me parked on the side of the road.

I just want to make this last effort into this repair the last, so any assistance is greatly appreciated.

Cheers
 

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Everything between the lift pump and the fuel tank is less than atmospheric pressure when the engine is cranking or running. This is where air can enter the fuel lines.
After the lift pump the fuel is under pressure and will not let air in.
The O rings are tricky because, under pressure they may not leak, but as soon as you place them under vacuum, they can let air in.
A small amount of air is not going to affect the engine running, but if you see bubbles, then you should fix it as soon as you can.
Remember, leaks get bigger, they do not get smaller or stay the same.
I think that is why the fuel lines are clear. So you can detect bubbles in the fuel lines.
I don’t know if you have already done this, but I would check the rubber fuel supply line where it joins to the clear pipe that runs to the fuel filter. Check the fitting on the clear pipe on the fuel filter. Change the fuel filter. Check the clear pipe from the fuel filter to the lift pump and the fitting on the inlet side of the lift pump.
After reading what you wrote, the air bubbles are coming from the filter. Therefore the leak is between the lift pump inlet pipe and the rubber fuel supply line from the tank.
When in doubt, throw it out. I also replaced that clear line from the rubber pipe to the filter because I didn’t want any issues.
Are these connections good on your engine?
(See arrows in photo)
  • 4E3D426C-D03A-4994-9291-DCB952C9B2FD.jpeg
 
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