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Fuel tank / sending unit / guage

Discussion in '365 GT4 2+2/400/412' started by SouthJersey400i, Sep 24, 2008.

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  1. SouthJersey400i

    SouthJersey400i Formula 3

    Mar 14, 2007
    1,679
    Romulus, NY (Finger Lakes)
    Full Name:
    Ken Battle
    #1 SouthJersey400i, Sep 24, 2008
    Preamble:
    1. Since I have had the car (2 years) most of the time after "filling" the gauge reads 3/4 or a bit more.
    2. Gauge swings +/- 1/2 volume on exit ramps and hills; I assume we all have that.
    3. This weekend touring the Finger Lakes I started with a "full" tank at 3/4+ and was going along fine for 150 plus miles and gauge dropped to 1/4 to 1/2 as I would expect. After a short winery stop, I noticed the gauge reading over 3/4 and and slowly reduced from there. Over the next 100 miles it trended down but I was totally lost when to fill it up.
    4. I filled the tank and gauge was pegged at 4/4+. It took about 17 gallon. I did 50++ miles before it dropped below that mark.
    5. Heading home it dropped down and seemed to be reading "normally" again.
    6. I refilled just before home with the tank at about 1/4 and was sure to get tank real full; it took 24. I did the pumping (in spite of NJ rules) and when I cut off the pump, there was a blub-blub-blub coming from the filler nozzle.

    Analysis:
    1. Between steps 3 and 5 I figured I would be posting here about what is the more likely failure sending unit or gauge and I would be asking where the sender is located and how to test it. Forget that.
    2. I am now convince I have an issue with equalizing the two sides of the tank (or two tanks if you see it that way).

    Questions:
    1. How are the tanks equalized? Is there a "bridge" between the top of the two tanks? Where does it run and is it likely to get pinched closed?
    2. Anyone had similar symptoms? If so, how did you fix it?

    I have not yet dug into my manuals and diagrams, but this forum is so good at flushing out issues I got to the computer first. Hope to hear from a few of you soon.

    Ken
     
  2. blkprlz

    blkprlz Formula 3

    Mar 24, 2007
    2,169
    Tampa bay
    Full Name:
    Bruce
    #2 blkprlz, Sep 25, 2008
    Last edited: Sep 25, 2008
    Ken,
    Definitely check your parts manual for pictorial rep. The sending unit is located in the right fuel tank, to remove the right side false floor, I found it easier to first remove the spare tire floor cover by unbolting one hinge (might as well do the right side while you are there). There are 3 screws that secure the tank floor cover...
    1. upper forward corner of the power antenna/vent hoses cover,
    2. upper right side of same cover (both of which are revealed by pulling back on carpeting over cover)
    3. above the structural member (for bumper) @ taillight end (lift up back carpet wall to expose).
    The floor cover & antenna cover are riveted together, it's a little tricky removing the whole assy.
    Voila, sending unit.
    After removing spare tire, you'll see a small tank (coined 'additional') that connects the two 16 gal. tanks of which feeds the pumps. The 'bridge between the top' are the vent hoses that are routed along the rear seat wall & connect to a vent box of sorts (I'm real curious how this works/fault check). A kinked vent line would definitely cause similar problems.
    W.R.T. blub-blub-blub, do you have the unleaded restrictor plate in your fill nozzle? Mine escaped this and sticker add-ons.
    Bruce

    Edit: I also found it easier to remove the structural member before the tank floor (15mm front, 13mm rear IIRC).
     
  3. SouthJersey400i

    SouthJersey400i Formula 3

    Mar 14, 2007
    1,679
    Romulus, NY (Finger Lakes)
    Full Name:
    Ken Battle
    #3 SouthJersey400i, Sep 25, 2008
    Bruce
    Thanks for the instructions. The rivets are out of my side panel so that will make it easier; I wondered how to redo the rivets and now I know. I am real curious about this 'additional' tank. Sending unit in right tank, makes sense for my filling problem since it is on the far side from the filler.

    I'll update status during the weekend.
    Ken
     
  4. It's Ross

    It's Ross Formula 3

    Jul 30, 2007
    2,028
    Barrington, Ill. USA
    Full Name:
    Ross
    #4 It's Ross, Sep 26, 2008
    I would be suspicious of a poor ground or other connection to the sender.
     
  5. 400iGuy

    400iGuy Formula 3
    Owner Rossa Subscribed

    Aug 26, 2004
    1,076
    Central Florida
    Full Name:
    Al
    #5 400iGuy, Sep 26, 2008
    Last edited by a moderator: Sep 7, 2017
    I read the above instruction and thought, I don't have a hinge. So I went and looked. What I have are 3 bolts where the hinge is supposed to be. It appears that it should mount to the pin in the last photo. Can someone provide a photo of the hinge. I expect that it's something simple enough that I can make a close approximation of it.

    Al
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  6. blkprlz

    blkprlz Formula 3

    Mar 24, 2007
    2,169
    Tampa bay
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    Bruce
    #6 blkprlz, Sep 26, 2008
    Last edited by a moderator: Sep 7, 2017
    Al,
    Where those 3 holes are is where this piece goes (positioned in the installed mode), be very careful w/tightening those little nuts, not much metal to those studs (which are missing from your floor). One of mine snapped so I'm in the same boat.
    Bruce
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  7. blkprlz

    blkprlz Formula 3

    Mar 24, 2007
    2,169
    Tampa bay
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    Bruce
    #7 blkprlz, Sep 26, 2008
    Last edited: Sep 26, 2008
    Ken,
    Rivets were out of mine as well, I found out how tricky it is to remove when I pulled the left side. So I re-padded the rt. floor w/slightly thicker foam & didn't rivet back together. It fits snug as a bug when reinstalled & is easy to remove for access for whatever.
    There are 1"+ hoses connecting the 2 tanks via additional tank (refer to IPB), so fuel flows into the right tank during fill up (unless the vent hose is kinked or obstructed). And as Ross mentioned, grounds is the first place to look if a fault lies in the electrics. You'll see a ground wire connected to one of the mounting studs for the sending unit, I'd pull the unit out to inspect while you're at it.
    Bruce
     
  8. 400iGuy

    400iGuy Formula 3
    Owner Rossa Subscribed

    Aug 26, 2004
    1,076
    Central Florida
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    Al
    #8 400iGuy, Sep 26, 2008
    Bruce,

    Thanks for the photo. I guess it doesn't show up very well but I have all 6 studs still there. It looks easy enough to reproduce. I just need to find some tubing that fits over the pin and nuts to fit the studs.

    Al
     
  9. blkprlz

    blkprlz Formula 3

    Mar 24, 2007
    2,169
    Tampa bay
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    Bruce
    #9 blkprlz, Sep 26, 2008
    Al,
    I'd remove the spare tire, maybe the nuts (black acorn type) are rolling around down there.
    Bruce
     
  10. SouthJersey400i

    SouthJersey400i Formula 3

    Mar 14, 2007
    1,679
    Romulus, NY (Finger Lakes)
    Full Name:
    Ken Battle
    #10 SouthJersey400i, Sep 26, 2008
    Bruce and Ross
    I'll tear into it tomorrow. A kinked or otherwise blocked hose sounds like the problem. I'm not sure how a ground problem would give blub-blub-blub!
    Ken
     
  11. blkprlz

    blkprlz Formula 3

    Mar 24, 2007
    2,169
    Tampa bay
    Full Name:
    Bruce
    #11 blkprlz, Sep 27, 2008
    Ken,
    The ground issue was meant for a elec./guage prob., hopefully you'll find a kinked hose/easy fix to the problem.
    Bruce
     
  12. SouthJersey400i

    SouthJersey400i Formula 3

    Mar 14, 2007
    1,679
    Romulus, NY (Finger Lakes)
    Full Name:
    Ken Battle
    #12 SouthJersey400i, Sep 28, 2008
    Bruce and others
    I dismantled all yesterday. I found that there is probably 1-2 ml of liquid in the float. This would give a low reading as I have seen. It does not explain why got full readings this past weekend nor does it explain the blub-blub. Ground is good. I took resistance readings:
    - float full down 335 ohm
    - float full up 10 ohm
    Does anyone know the specs on these readings?

    The float did not seem to have a crack or pin hole. Maybe it is 25 years of diffusion thru the plastic. Maybe a neutral fluid is injected into the float to get an exact weight or to adjust calibration. Can anyone confirm that their 400i float has NO liquid in it? Tank was very full when I pulled the sending unit and the gauge reads full.

    The float can easily be popped off the end of the pivot arm. Does anyone know if it can be replace? From? Sending unit is Veglia.

    As for the blub-blub, the vent pipe across from the far tank (RH) to the filler cap has no blockage. There is a vent tank of some kind on the parts blowup, but it must be located behind the rear A/C unit and therefore not really acccessible. However, I disconnected the vent line at right side and blew through line and there is no back pressure or gurgling.

    So I have two questions above, if anyone can help out.
    Ken
     

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