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Thread: Weird fuel sending unit problem!!

  1. #1
    Registered User Da Flash's Avatar
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    CZCC-3103
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    Nov 2002
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    Default Weird fuel sending unit problem!!

    I recently dropped my fuel tank on my '71 240z to get it acid washed and applied the Por-15 tank sealer kit to it and Por-15 the outside, while I was at it I decided to install a new sending unit and O-ring so that I wouldn't have to mess around with the tank for years to come!! All seemed to go well but after about a week my fuel gauge reads either very full or about 7/8th of a tank. I decided to remove the sending unit to see if it would read correctly outside of the tank, I first checked the connections, all seemed well and there were no loose fittings nor any change to the gauge when I jiggled/tweaked them. After I removed the unit the gauge would respond to moving the arm up and down but as soon as I reinstall it the gauge would return to it's incorrect reading!!! I noticed that some of the sealer was on the securing ring, so I sanded it off thinking maybe if the ring didn't have a good contact with the unit, that it would give incorrect reading but, it still reads wrong!

    Is there something that I'm doing wrong? Is the O-ring supposed to keep the unit from coming in contact with the tank, thereby not creating this grounding problem that I'm experiencing??

    Any and all suggestion will be greatly appreciated!!
    '71 240z, L28/N42 block, flattop pistons, mildly ported and polished N42 head, ZX 5-speed, stock SU's, ZX Dizzy w/12-80, 6-2-1 header, 2.5" mandrel bend exhaust, tokico illuminas and springs, all new polyurethane bushings. Runs great but, looks like crap!!! 1991 300ZXTT that's a work in progress!!

  2. #2
    Registered User Da Flash's Avatar
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    Default

    Well I guess this was one of those things that others don't run into very often. Thankfully some lengthy investigation revealed the problem as being that the new and improved insulation between the straps and tank, (well I guess it wasn't improved!) wasn't wide enough to keep the straps from contacting the tank. Apparently if the straps come in contact with the tank, there is some type of short that causes the fuel sending unit to malfunction. After some wider rubber strips the problem was solved !! Now to tweak the arm of the sending unit to read a little more accurately !!
    '71 240z, L28/N42 block, flattop pistons, mildly ported and polished N42 head, ZX 5-speed, stock SU's, ZX Dizzy w/12-80, 6-2-1 header, 2.5" mandrel bend exhaust, tokico illuminas and springs, all new polyurethane bushings. Runs great but, looks like crap!!! 1991 300ZXTT that's a work in progress!!

  3. #3
    beandip beandip's Avatar
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    CZCC-1887
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    Default

    if this is he solution to the malfunction that's great . I have never heard of this being the problem or the solution to a malfunctioning sending unit. Thanks for the follow up post. Gary
    I'd rather die while I am living than live while I am dieing. CZC 1887 IZCC 12602 Member of NorthWest Z Car Club

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