air in fuel

[blockw5chips]

I'm having a problem w/ air in the fuel:mad: . I put the clear tube on the IP return and I'm getting bubbles/foam. I was told the lift pump was bad. Removed mech. LP and replaced w/ carter p4070 elec. pump. I mounted it behind the rt rear leaf spring hanger. I pulled the tank and replaced all the rubber lines. I connected my primary filter to the secondary filter. The only rubber hose I didn't replace was the one running from secondary filter to IP. I bled air out of the lines, then I fired it up. (Starts much easier now):) Monday and Tuesday I drove to and from work no problems:D . Wednesday I started to work and I noticed it wasn't running as usual(didn't have any power). I thought maybe just rainy weather. I drove home and anytime I came to a stop it would idle real rough and act like it was going to bog down and quit. I would put it in neutral and push the pedal a little to keep it going. A couple of times it stalled on me, but would usually crank back up. Then before I got home, it would bog down and wouldn't go any faster(even if I pushed pedal to floor,or put it in neutral and try revving up just a little). Today, I went out and checked fuel lines. I jumped power to all three connection on top of the IP, everything works. So I start up, everything looks good, no air in return line. I take it for a spin around neighborhood runs good. I leave for work and as soon as I pull out and start to accelerate it bogs down. I head for home, I check return line and it got bubbles, I open throttle up a little and the bubbles clear up. Then it starts making bubbles again, I rev it up and it starts to clear up but when I release the throttle it gets tons of bubbles and this time foam. I rev it up again and it won't clear up the bubbles but the foam goes away. Then when I let off it bubbles/foams and dies. So I left it cause I have to get to work. Can a bad IP generate bubbles and foam or does it start before that? I figured w/ the electric fuel pump being back by the tank the only place to suck air would be between the pump and tank, but then I don't know because I'm fairly new to diesels. Ive only own this one for about 1 yr. Any thoughts or comment would be appreciated.

Thanks.

[Subzilla]

Also, should the injector return lines be filled with fuel all the time? I'm asking the population this question to go along with the above questions.

[john8662]

You can also get a leak from the fuel filters themselves, well in mating to the housing(s).

You have two, check for rotted or bad gaksets. Have both fuel filter been serviced?

Make sure that the Primary fuel filter gets primed with fuel prior to starting. You'll have an air lock in that filter if not. I ran mine out of fuel recently, and it's still getting air from that location.

You can remove the filter and manually fill with fuel or use the air drain valve on the top of the filter unil you quit getting air bubbles out of it (messy) and start getting a steady stream of fuel.

The symptoms stated are EXACTLY how an engine behaves with air in the system. You can rev the engine up too and the bubbles will appear to go away too, I've noticed this as well.

Subzilla,

The return lines should retain fuel, the return at the injection pump should remain full of fuel as well, otherwise you've got a leak allowing fuel to return through the supply side.

Leaking fuel return lines cause running/starting issues as well.

Even the little bugger on the top of the pump, I've now started throwing away all the quick-connect clamps on the 1/4" ID lines, and replacing them with hose clamps.

[Robyn]

Pull the fuel line off the last filter where it heads for the IP. Fire up the electric fuel pump and let it pump through a clear tube into a clean glass jar. Submerge the line and see if you are getting bubbles. If so you have an air leak somewhere between the tank and the engine.
Or you can plug the line going to the IP and pressure up the fuel lines with the electric pump and look for leaks.
You could have an air leak in the tank inn the sending unit/screen assembly.
This is not real common but can happen.
Check these things and report back what you find.
Good luck
Robyn

[Subzilla]

Need some education here. I still don't understand why there is any fuel in the fuel return line in the first place. If the IP is pushing a set, defined amount of fuel at a certain time through the injector, I'm having trouble understanding why there is any excess fuel not popping through the injector and ending up in the return lines. Why would there such an amount that would keep these lines full? I've always read on TDP that clamps are not even neceassary as these return lines have no pressure to them. I use no clamps and just had my first leak with one of the end caps. It actually just softened up and I cut a piece of the fabric covered return lines, wired a screw in the end and shoved it on the fitting - no more leaks.

[john8662]

You'll want to use the clamps on the endcaps, but not on the rest of the return lines. There really isn't any pressure, just some volume of fuel in the lines. Supposedly in a sealed system.