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Old 04-18-2014, 02:57 PM
palmtree palmtree is offline
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Default How is the fuel tank vented

I seem to be getting some sort of vacuum in my fuel system. I was having trouble starting it and so I installed a bulb style hand pump and some clear lines so I could see what is going on. If I have someone crank it over while I pump the bulb it will start and run. Then when I shut it down I can barely hear the squeak of some air getting in and will slowly see bubbles forming in the clear fuel line. If I try to start it without someone pumping the bulb then I can see the bubbles just sitting in the line. Fuel doesn't seem to move (I assume it is air locked).
I can't tell how the tank is vented. I have a hose that runs from up near the filler neck and hangs down open near the tank. Should the open end of this line be attached to the tank somewhere?
Any ideas?
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Old 04-18-2014, 06:09 PM
ngoma ngoma is offline
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What kind of vehicle?
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Old 04-18-2014, 07:29 PM
palmtree palmtree is offline
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Quote:
Originally Posted by ngoma View Post
What kind of vehicle?
Oh, sorry. It's a 1980 265 with d24.
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Old 04-20-2014, 11:00 AM
v8volvo v8volvo is offline
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IIRC the 700 series diesel cars have an open tank vent with some type of rollover valve that closes the vent if the car ends up with the wheels in the air.

Do you see or smell any evidence of fuel leakage around the back of the engine? This sounds a little like a leaky injection pump driveshaft seal.
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Old 04-20-2014, 11:25 AM
palmtree palmtree is offline
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Thanks for the info. It's a 1980 265. I don't see any fuel leaks. It's funny sometimes when I pump the hand bulb I can hear the air expelling into the tank (bubbling) and then when the air is out I am no longer able to pump the bulb. It's driving me crazy how I can hear the very faint squeak of air after depressing the bulb but I can't tell exactly where it is coming from.
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Old 04-20-2014, 06:14 PM
ngoma ngoma is offline
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Try it with the fuel fill cap off (fuel tank completely vented)-- does it do the same thing?
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Old 04-23-2014, 09:38 AM
palmtree palmtree is offline
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I ran the car again today. Gave the bulb a few pumps (till I stopped hearing air bubbling in the fuel tank) then she fired right up. Drove fine for a couple miles even under acceleration. Shut it down and could see bubbles starting to form in the clear fuel line. I listened really close and it sounded like the squeak of air was coming from one of the injectors or possibly a hard line. Tightening the hard lines is easy but I have never messed with the injectors. Anything special I need to know before I start wrenching on them? Also how are the return lines connected to the injector? Mine are covered in some kind cloth looking stuff so I can't see.
Thanks again.
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Old 04-23-2014, 12:41 PM
ngoma ngoma is offline
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Where is your clear line placed? Which way do the bubbles move? What happened when you tried with the fuel filler cap off?

Quote:
Originally Posted by palmtree View Post
Tightening the hard lines is easy but I have never messed with the injectors. Anything special I need to know before I start wrenching on them?
Yes. DO NOT overtighten them! You're talking about the injector line connectors, right? The injector line connections are easily damaged by overtightening. Torque spec. on the injector line nuts is 18 ft-lbs. If you have a torque wrench, practice on some other nuts or bolts to get a feel for 18 ft-lbs.

More importantly, air ingress via the injector lines is likely not your problem. If they were loose, wouldn't you expect to see fuel leakage during (> 2000PSI fuel pressure there!) operation? My opinion is you are barking up the wrong tree.

Quote:
Originally Posted by palmtree View Post
Also how are the return lines connected to the injector? Mine are covered in some kind cloth looking stuff so I can't see.
Those woven lines work like the Chinese finger trap, i.e., the harder you pull, the tighter it gets. Very difficult to remove them without damaging them. Best method is to slowly work them off the barbs by slipping a small screwdriver under the end and pry up, each side, a little at a time. Unless they are 2-3 weeks new, they are not coming off without damage. Most of us just cut them off above the nipple, and slice off the remaining, taking care not to nick or score the barbs. When installing new, we cut them quite a bit longer than needed, to provide a few on/off encounters during their lifetime before they grow too short. Are yours leaking fuel?
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Old 04-24-2014, 08:35 AM
palmtree palmtree is offline
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Thanks again for the help.
The clear tubing is placed between the hardline from the tank and the filter.
The bubbles are coming from the filter side (running backwards in the tubing).
I did take the cap off and ran the car a while -- then had the same bubbles when I shut it down. I guess I'm not getting a vacuum in the fuel tank after all.
Anyone have any good "shop tricks" for zeroing in on where that air squeak is coming from? It may not be anything -- there are always some noises when an engine is shut down. This just sounded so much like air being sucked that I had to check it out.
Is it a bad idea to install a low pressure electric pump before the filter? I wouldn't want to damage anything more.
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Old 04-24-2014, 09:09 AM
ngoma ngoma is offline
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1. When did this problem start happening? After a fuel filter replacement? Some time after running biodiesel?

2. What is the condition of the fuel hose between fuel filter <==> IP?

3. Have you checked that the banjo fittings on the filter head are tight? Hose clamps? Air bleed screw?

4. Does the fuel filter have a drain valve at the bottom?

As you can see, I'm concentrating on the area around the fuel filter/filter head. Can you add a section of clear fuel hose immediately downstream of the filter? That way we could perceive better the source of air ingress.

Low pressure (<5 PSI) electric fuel pump should be OK.

No clue about any squeak after shutdown. Have you tried using a mechanics stethescope?
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