Fighting air leaks in the fuel system, kind of a long post

[spencnaz]

Hello all,

It's been a frustrating weekend. After months of trouble free service, my truck is stalling a dying from a persistent air leak. I was stuck on the highway a few times on Saturday getting down to Puyallup here in the Seattle area.

Here's the situation:

1. You all know what it's like when your truck runs out of fuel, starts slowing down, no power and it dies. Same happens here.

2. I installed a clear fuel filter for a gasser with the element removed to watch for any air bubbles. It's installed on the line where the water/fuel separator would be. When the engine is running, I can see a steady stream of bubbles being made from the side that sucks from the front fuel tank (i've not used the rear tank due to it getting filled with gunk it will be drained and cleaned this summer). I put in a new section of fuel line since biodiesel degrades rubber compounds with re-tightened fuel hose clamps.

3. I looked over the fuel lines coming from the tank and there are no apparent fuel leaks, I checked the connections at the tank and their tight as well, I put in new retaining clips a few months ago. I put in new fuel injector return caps and hoses last summer. A new fuel pump and IP were installed last September as well (sure hope the IP isn't going on me, but with the amount of air coming into that clear fuel filter, I think the IP is just fine.)

With that out of the way, my question is this:

Could this be a problem with the fuel selector valve? Does this valve contain any rubber parts such as o-rings that would be attacked by ULSD or biodiesel?

Sorry for the long post guys, I like to keep things short and to the point but I want to be as detailed as possible to narrow what the hell is going on here.

 

[towcat]

This is going to sound crazy and really off the wall, but I just went through diagnosing this one. Are you getting excessive pressure on the return side and has your feul consumption went through the roof recently? Also, install pcv tubing on the return side between the cap and the feul filter and check for bubbles too. If so, check for the pattern of bubbles while running and after shutdown.

 

[spencnaz]

no, fuel consumption doesn't seem to be out of the ordinary.

I'm not sure about the excessive pressure on the return side as I do not have a gauge to measure that pressure. I notice that the clear fuel filter that I installed will continue to fill up when the engine is shut off, so there is a good seal from that filter to the lift pump. The air bubbles are coming from the side that goes to the fuel tank leading me to believe that the fuel leak is there some where.

Of course getting that hose on to the fuel line is a real bear, especially if the engine has just been shut off.

What cap are you talking about? The cap that's on the fuel filter head?

 

[towcat]

you should have a return line running from the filter head to those danged injector caps. I can post a pic later on today. Anyhow, the problem on this truck was isolated to a feul switching valve sticking. Not a very obvious problem at all, but there was no other sources of the air intrusion until the return pressure built up to the point the motor shut down.

 

[spencnaz]

Towcat, would you be able to directly email these pictures? Just send me a private message via this site and I'll give you my direct email address.

ps, I ordered some biodiesel resistant fuel line today.

 

[Exekiel69]

The fuel tank selector does have o-rings and I guess they can be affected by BD just like any regular fuel hose so that is an option. You'll find the same o-rings on the fuel tank feed and return lines.

 

[spencnaz]

Would a leaking o-ring in the FSV be enough to burp that much air into the fuel system?

I pretty certain it's on the fuel inlet side of the system, the line that comes from the tank to where the fuel water separator was. I've since bypassed that pain-in-the-neck.

Just had another thought:

I have a 50 gallon extra fuel tank in the bed of the truck that wasn't cleaned out by biodiesel. It drains by gravity into the forward tank keeping it full until the 50 gallon tank drains completely. I pulled the fuel filter this morning when I was stuck on the side of the road and noticed some brown liquid (obviously not biodiesel or diesel fuel ) come out of it. Could it be that I loosened a bunch of crap from that 50 gallon tank and it made it's way to the fuel filter?

It still doesn't explain the bubbles in the fuel system but it's a start I guess.