Air bubbles in fuel lines

[bj74redrider]

RufusTheDufus It's very strange that you have so much stuff coming out of the return line at idle or a little above idle. This is not normal.

It will pump about 3 ounces of foamy diesel every 2 seconds or so. I'm thinking it is a seal inside the IP. I wont rebuild it untill I have tried everything else though.

 

[RufusTheDufus]

Have you tried disconnecting the return line and routing it to a catch can? You will have to plug it off where the hose connects near the lift pump so it doesn't suck air. The goal would be to not put the air/foam from the return line back into the injection pump.


Have you bled the injection pump? You've mentioned bleeding air at the fuel filter and cracking open the injectors. There's also a bleed screw on the side of the injection pump too. Have you used it to get the air out of the pump?

 

[Squash]

Shot in the dark.

Does your tank have a vent line?
Should be a hose from tank to somewhere in the frame.

Pulled mine off and found it was plugged therefore a rush off air when the fuel cap is removed.
Pull yours off if so equiped and blow air through line and check valve, if plugged clean it out and try again.

A plugged vent would cause air to be sucked in from any where...


90917-10020 is your part number

 

[bj74redrider]

I don't want to jinks it, but it seems to be running ok now. I replaced the banjo bolt washers at all the fuel filter connections. 2 washers were very worn including the one connecting to the injector pump and the rubber part of the washer almost looked like it was melted.

Have you tried disconnecting the return line and routing it to a catch can? You will have to plug it off where the hose connects near the lift pump so it doesn't suck air. The goal would be to not put the air/foam from the return line back into the injection pump.

i will try this next.

Have you bled the injection pump? You've mentioned bleeding air at the fuel filter and cracking open the injectors. There's also a bleed screw on the side of the injection pump too. Have you used it to get the air out of the pump?

I never have done this, would air get trapped in there, or would eventually work its way out while it is running? Wouldn't the air work it's way to the filter bleed screw?

Does your tank have a vent line?
Should be a hose from tank to somewhere in the frame.

I had the same thought, so I disconnected the check valve at the filler neck because it is easier to get at, and it made no difference.

Thanks for the ideas guys.

 

[RufusTheDufus]

I never have done this, would air get trapped in there, or would eventually work its way out while it is running? Wouldn't the air work it's way to the filter bleed screw?

The air would not make it's way to the filter bleed screw. The filter is before the injection pump. The air would make its way to you injectors and cause foam to come out of the return line. You can follow the process of properly bleeding the air from your fuel system in this post with photos.

 

[Nuabie]

I posted this for a similar thread some time ago. Perhaps some of this will be helpful.

The IP has two "pumps", the first ( on the side of the IP) is the transfer pump that moves fuel from the tank to the IP.

A good check is to remove the fuel line from the transfer line and put clear plastic fuel line from the transfer pump into a container of diesel on the ground under the engine. Bleed the system with the primer pump (I like to keep a short - 10" or so - piece of clear line on the bleeder screw and keep it submerged in a plastic water bottle about half full of clean diesel - that keeps air from coming back into the system and avoids the mess associated with bleeding the system).

Start the engine, let it run for a while and see if there is any air in the supply line.

If there isn't, shut the engine down and keep an eye on the clear line. If bubbles start to move through the line you know that you have a leak in the primer or the line from the injector return line to the banjo fitting on the transfer pump. There is short piece of flex line at the back of the return rail that goes onto a steel line that runs behind the intake manifold down to the transfer pump.

A leak in that 3" line took me 2 days to isolate and 5 minutes to fix!

The clear line to the transfer pump was the answer for me but for all it takes to change that line it is worth it to assume that it might be leaking and replace it.

Of course all of the other suggestions you are getting could also be the problem.

Good luck!

Your 15 year old post helped sort out my air in the fuel line issues. Replaced the primer which sorted some of it but it was the 3" line that was the main cause. Thanks for your help !