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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? |
#2
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What kind of vehicle?
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1985 744 gle d24t 1985 745 gle d24t |
#3
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#4
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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. |
#5
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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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#6
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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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1985 744 gle d24t 1985 745 gle d24t |
#7
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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. |
#8
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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:
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:
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1985 744 gle d24t 1985 745 gle d24t |
#9
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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. |
#10
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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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1985 744 gle d24t 1985 745 gle d24t |
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